CiteULike: Tag basal-ganglia

Motor deactivation in the human cortex and basal ganglia.

William R Marchand — 2007-10-09T02:41:01-00:00

Neuroimage (9 August 2007)

We used a functional magnetic resonance imaging motor activation paradigm for both hands and functional connectivity analyses to investigate motor deactivation. These analyses revealed ipsilateral (to the task) postcentral gyrus connectivity with the ipsilateral primary motor cortex as well as contralateral cerebellum for both hands. Analyses using default-mode network nodes as seed regions revealed connectivity patterns similar to previous studies of the default network and therefore provide evidence that this network is demonstrable using a synchronized motor activation paradigm. We did not find evidence suggesting that motor deactivation represents modulation of the default mode network. Therefore, motor deactivation is likely a motor-specific process. Finally, we found no evidence of basal ganglia circuit deactivation, which suggests that the two-pathway hypothesis of frontal-subcortical circuit function may be incomplete.

Timing and prediction the code from basal ganglia to thalamus.

SW Bottjer — 2007-02-14T17:17:34-00:00

Neuron, Vol. 46, No. 1. (7 April 2005), pp. 4-7.

When is an inhibitory synapse not inhibitory? In this issue of Neuron, Person and Perkel demonstrate that thalamic neurons can translate extrinsic GABAergic input from the basal ganglia into highly precise patterns of sustained spiking in a circuit that is essential for vocal learning in songbirds. Postinhibitory rebound serves as a mechanism that preserves precise spike timing information, enabling reliable propagation of activity throughout this pathway. The results have broad implications for basic mechanisms of functional processing in both thalamus and basal ganglia and serve to increase our understanding of how acoustic units of vocal sounds are transformed into motor gestures during the sensitive period for song learning.

Dissociable roles of ventral and dorsal striatum in instrumental conditioning.

J O'Doherty — 2006-02-01T20:02:54-00:00

Science, Vol. 304, No. 5669. (16 April 2004), pp. 452-454.

Instrumental conditioning studies how animals and humans choose actions appropriate to the affective structure of an environment. According to recent reinforcement learning models, two distinct components are involved: a "critic," which learns to predict future reward, and an "actor," which maintains information about the rewarding outcomes of actions to enable better ones to be chosen more frequently. We scanned human participants with functional magnetic resonance imaging while they engaged in instrumental conditioning. Our results suggest partly dissociable contributions of the ventral and dorsal striatum, with the former corresponding to the critic and the latter corresponding to the actor.

The basal ganglia in human learning.

CA Seger — 2006-08-16T21:58:22-00:00

Neuroscientist, Vol. 12, No. 4. (August 2006), pp. 285-290.

For many years, the basal ganglia were described in anatomy courses as strictly motor structures. Certainly, some of the most obvious and debilitating symptoms shown by persons with basal ganglia disorders are problems in motor control. However, the basal ganglia are not limited to motoric aspects of behavior: recent research shows that they are involved in most areas of cognitive and emotional functioning, consistent with their anatomical connections with all areas of the cortex. This review will focus on the roles of the basal ganglia in human learning, particularly sequence learning and category learning. Current areas of research that are discussed include the differing roles of different basal ganglia regions, patterns of interaction between the cortex and basal ganglia, differences in positive and negative association learning, effects of dopaminergic medication on learning, whether basal ganglia-mediated learning is implicit or explicit, and how the basal ganglia learning systems interact with other learning systems, particularly within the medial temporal lobe.

Re-emergence of striatal cholinergic interneurons in movement disorders

Antonio Pisani — 2007-10-06T11:16:25-00:00

Trends in Neurosciences, Vol. In Press, Corrected Proof

Twenty years ago, striatal cholinergic neurons were central figures in models of basal ganglia function. But since then, they have receded in importance. Recent studies are likely to lead to their re-emergence in our thinking. Cholinergic interneurons have been implicated as key players in the induction of synaptic plasticity and motor learning, as well as in motor dysfunction. In Parkinson's disease and dystonia, diminished striatal dopaminergic signalling leads to increased release of acetylcholine by interneurons, distorting network function and inducing structural changes that undoubtedly contribute to the symptoms. By contrast, in Huntington's disease and progressive supranuclear palsy, there is a fall in striatal cholinergic markers. This review gives an overview of these recent experimental and clinical studies, placing them within the context of the pathogenesis of movement disorders.

Different brain circuits underlie motor and perceptual representations of temporal intervals.

D Bueti — 2008-02-27T18:43:15-00:00

J Cogn Neurosci, Vol. 20, No. 2. (February 2008), pp. 204-214.

In everyday life, temporal information is used for both perception and action, but whether these two functions reflect the operation of similar or different neural circuits is unclear. We used functional magnetic resonance imaging to investigate the neural correlates of processing temporal information when either a motor or a perceptual representation is used. Participants viewed two identical sequences of visual stimuli and used the information differently to perform either a temporal reproduction or a temporal estimation task. By comparing brain activity evoked by these tasks and control conditions, we explored commonalities and differences in brain areas involved in reproduction and estimation of temporal intervals. The basal ganglia and the cerebellum were commonly active in both temporal tasks, consistent with suggestions that perception and production of time are subserved by the same mechanisms. However, only in the reproduction task was activity observed in a wider cortical network including the right pre-SMA, left middle frontal gyrus, left premotor cortex, with a more reliable activity in the right inferior parietal cortex, left fusiform gyrus, and the right extrastriate visual area V5/MT. Our findings point to a role for the parietal cortex as an interface between sensory and motor processes and suggest that it may be a key node in translation of temporal information into action. Furthermore, we discuss the potential importance of the extrastriate cortex in processing visual time in the context of recent findings.

Basal Ganglia Play a Unique Role in Task Switching within the Frontal-Subcortical Circuits: Evidence from Patients with Focal Lesions.

Einat Yehene — 2008-02-04T21:25:25-00:00

J Cogn Neurosci (22 January 2008)

Abstract The performance of patients with lesions involving the basal ganglia (BG) was compared to that of patients with prefrontal (PFC) lesions, thalamic (TH) lesions, and age-matched controls in order to examine the specific role of the BG within the frontal-subcortical circuits (FSCC) in task switching. All the BG patients and none of the other participants showed a marked increase in error rate in incongruent trials where correct responses depended upon the choice of the correct task rule. Some BG patients erred in failing to switch tasks and others failed despite their attempt to switch tasks. Additionally, reaction time results indicate abnormal response repetition effects among the BG patients; failure in benefiting from advance task information among all the patients; and increased task mixing costs following PFC lesions. The authors conclude that although the frontal-subcortical circuits jointly determine some behaviors (such as benefiting from preparation), the BG play a unique role within the FSCC in action selection and/or the inhibition of irrelevant information.

The Neural and Computational Basis of Controlled Speed-Accuracy Tradeoff during Task Performance.

Vincent van Veen — 2008-04-23T15:03:28-00:00

Journal of cognitive neuroscience (16 April 2008)

Abstract People are capable, at will, of trading speed for accuracy when performing a task; they can focus on performing accurately at the cost of being slow, or emphasize speed at the cost of decreased accuracy. Here, we used functional magnetic resonance imaging to investigate the neural correlates of this ability. We show increased baseline activity during speed emphasis in a network of areas related to response preparation and execution, including the premotor areas of the frontal lobe, the basal ganglia, the thalamus, and the dorsolateral prefrontal and left parietal cortices. Furthermore, speed emphasis was associated with reduced transient response-related activation in several of these structures, suggesting that because of the greater baseline activity under speed emphasis, less activation is needed in these structures to reach response threshold, consistent with the assumptions of several computational theories. Moreover, we identify the dorsolateral prefrontal cortex as providing the top-down control signal that increases this baseline activity.

Cooperation of the basal ganglia, cerebellum, sensory cerebrum and hippocampus: possible implications for cognition, consciousness, intelligence and creativity

Rodney Cotterill — 2007-11-21T06:00:20-00:00

Progress in Neurobiology, Vol. 64, No. 1. (May 2001), pp. 1-33.

It is suggested that the anatomical structures which mediate consciousness evolved as decisive embellishments to a (non-conscious) design strategy present even in the simplest unicellular organisms. Consciousness is thus not the pinnacle of a hierarchy whose base is the primitive reflex, because reflexes require a nervous system, which the single-celled creature does not possess. By postulating that consciousness is intimately connected to self-paced probing of the environment, also prominent in prokaryotic behavior, one can make mammalian neuroanatomy amenable to dramatically straightforward rationalization. Muscular contraction is the nervous system's only externally directed product, and the signaling routes which pass through the various brain components must ultimately converge on the motor areas. The function of several components is still debatable, so it might seem premature to analyze the global operation of the circuit these routes constitute. But such analysis produces a remarkably simple picture, and it sheds new light on the roles of the individual components. The underlying principle is conditionally permitted movement, some components being able to veto muscular contraction by denying the motor areas sufficient activation. This is true of the basal ganglia (BG) and the cerebellum (Cb), which act in tandem with the sensory cerebrum, and which can prevent the latter's signals to the motor areas from exceeding the threshold for overt movement. It is also true of the anterior cingulate, which appears to play a major role in directing attention. In mammals, the result can be mere thought, provided that a second lower threshold is exceeded. The veto functions of the BG and the Cb stem from inhibition, but the countermanding disinhibition develops at markedly different rates in those two key components. It develops rapidly in the BG, control being exercised by the amygdala, which itself is governed by various other brain regions. It develops over time in the Cb, thereby permitting previously executed movements that have proved advantageous. If cognition is linked to overt or covert movement, intelligence becomes the ability to consolidate individual motor elements into more complex patterns, and creativity is the outcome of a race-to-threshold process which centers on the motor areas. Amongst the ramifications of these ideas are aspects of cortical oscillations, phantom limb sensations, amyotrophic lateral sclerosis (ALS) the difficulty of self-tickling and mirror neurons.

Deictic codes for the embodiment of cognition (with commentary)

DH Ballard — 2006-07-02T21:30:06-00:00

Behavioral and Brain Sciences, Vol. 20, No. 4. (December 1997)

To describe phenomena that occur at different time scales, computational models of the brain must incorporate different levels of abstraction. At time scales of approximately 1/3 of a second, orienting movements of the body play a crucial role in cognition and form a useful computational level--more abstract than that used to capture natural phenomena but less abstract than what is traditionally used to study high-level cognitive processes such as reasoning. At this "embodiment level," the constraints of the physical system determine the nature of cognitive operations. The key synergy is that at time scales of about 1/3 of a second, the natural sequentiality of body movements can be matched to the natural computational economies of sequential decision systems through a system of implicit reference called deictic in which pointing movements are used to bind objects in the world to cognitive programs. This target article focuses on how deictic binding make it possible to perform natural tasks. Deictic computation provides a mechanism for representing the essential features that link external sensory data with internal cognitive programs and motor actions. One of the central features of cognition, working memory, can be related to moment-by-moment dispositions of body features such as eye movements and hand movements.

The declarative/procedural model of lexicon and grammar.

MT Ullman — 2006-05-11T05:24:54-00:00

J Psycholinguist Res, Vol. 30, No. 1. (January 2001), pp. 37-69.

Our use of language depends upon two capacities: a mental lexicon of memorized words and a mental grammar of rules that underlie the sequential and hierarchical composition of lexical forms into predictably structured larger words, phrases, and sentences. The declarative/procedural model posits that the lexicon/grammar distinction in language is tied to the distinction between two well-studied brain memory systems. On this view, the memorization and use of at least simple words (those with noncompositional, that is, arbitrary form-meaning pairings) depends upon an associative memory of distributed representations that is subserved by temporal-lobe circuits previously implicated in the learning and use of fact and event knowledge. This "declarative memory" system appears to be specialized for learning arbitrarily related information (i.e., for associative binding). In contrast, the acquisition and use of grammatical rules that underlie symbol manipulation is subserved by frontal/basal-ganglia circuits previously implicated in the implicit (nonconscious) learning and expression of motor and cognitive "skills" and "habits" (e.g., from simple motor acts to skilled game playing). This "procedural" system may be specialized for computing sequences. This novel view of lexicon and grammar offers an alternative to the two main competing theoretical frameworks. It shares the perspective of traditional dual-mechanism theories in positing that the mental lexicon and a symbol-manipulating mental grammar are subserved by distinct computational components that may be linked to distinct brain structures. However, it diverges from these theories where they assume components dedicated to each of the two language capacities (that is, domain-specific) and in their common assumption that lexical memory is a rote list of items. Conversely, while it shares with single-mechanism theories the perspective that the two capacities are subserved by domain-independent computational mechanisms, it diverges from them where they link both capacities to a single associative memory system with broad anatomic distribution. The declarative/procedural model, but neither traditional dual- nor single-mechanism models, predicts double dissociations between lexicon and grammar, with associations among associative memory properties, memorized words and facts, and temporal-lobe structures, and among symbol-manipulation properties, grammatical rule products, motor skills, and frontal/basal-ganglia structures. In order to contrast lexicon and grammar while holding other factors constant, we have focused our investigations of the declarative/procedural model on morphologically complex word forms. Morphological transformations that are (largely) unproductive (e.g., in go-went, solemn-solemnity) are hypothesized to depend upon declarative memory. These have been contrasted with morphological transformations that are fully productive (e.g., in walk-walked, happy-happiness), whose computation is posited to be solely dependent upon grammatical rules subserved by the procedural system. Here evidence is presented from studies that use a range of psycholinguistic and neurolinguistic approaches with children and adults. It is argued that converging evidence from these studies supports the declarative/procedural model of lexicon and grammar.

Contributions of memory circuits to language: the declarative/procedural model.

MT Ullman — 2006-05-10T19:58:31-00:00

Cognition, Vol. 92, No. 1-2. (n 2004), pp. 231-270.

The structure of the brain and the nature of evolution suggest that, despite its uniqueness, language likely depends on brain systems that also subserve other functions. The declarative/procedural (DP) model claims that the mental lexicon of memorized word-specific knowledge depends on the largely temporal-lobe substrates of declarative memory, which underlies the storage and use of knowledge of facts and events. The mental grammar, which subserves the rule-governed combination of lexical items into complex representations, depends on a distinct neural system. This system, which is composed of a network of specific frontal, basal-ganglia, parietal and cerebellar structures, underlies procedural memory, which supports the learning and execution of motor and cognitive skills, especially those involving sequences. The functions of the two brain systems, together with their anatomical, physiological and biochemical substrates, lead to specific claims and predictions regarding their roles in language. These predictions are compared with those of other neurocognitive models of language. Empirical evidence is presented from neuroimaging studies of normal language processing, and from developmental and adult-onset disorders. It is argued that this evidence supports the DP model. It is additionally proposed that "language" disorders, such as specific language impairment and non-fluent and fluent aphasia, may be profitably viewed as impairments primarily affecting one or the other brain system. Overall, the data suggest a new neurocognitive framework for the study of lexicon and grammar.

The Role of the Dorsal Striatum in Reward and Decision-Making

Bernard Balleine — 2007-08-03T09:08:38-00:00

J. Neurosci., Vol. 27, No. 31. (1 August 2007), pp. 8161-8165.

Although the involvement in the striatum in the refinement and control of motor movement has long been recognized, recent description of discrete frontal corticobasal ganglia networks in a range of species has focused attention on the role particularly of the dorsal striatum in executive functions. Current evidence suggests that the dorsal striatum contributes directly to decision-making, especially to action selection and initiation, through the integration of sensorimotor, cognitive, and motivational/emotional information within specific corticostriatal circuits involving discrete regions of striatum. We review key evidence from recent studies in rodent, nonhuman primate, and human subjects. 10.1523/JNEUROSCI.1554-07.2007

Basal ganglia and cerebellar loops: motor and cognitive circuits

FA Middleton — 2006-01-06T14:04:35-00:00

Brain Research Reviews, Vol. 31, No. 2. (March 2000), pp. 236-250.

Re-evaluation of the functional anatomy of the basal ganglia in normal and Parkinsonian states

R Levy — 2008-03-19T00:32:14-00:00

Neuroscience, Vol. 76, No. 2. (January 1997), pp. 335-343.

In the late 1980s, a functional and anatomical model of basal ganglia organization was proposed in order to explain the clinical syndrome of Parkinson's disease. According to this model, the pathological overactivity observed in the subthalamic nucleus and the output station of the basal ganglia plays a crucial role in the pathophysiology of the motor signs of Parkinson's disease. The hyperactivity of subthalamic neurons in Parkinsonism is viewed as a direct consequence of a pathological hypoactivity of the external segment of the pallidum. This article reviews recent data from different experimental approaches that challenge the established model of basal ganglia organization by reinterpreting the functional interaction between the external segment of the pallidum and the subthalamic nucleus in both the normal and pathological state. Indeed, recent neurobiochemical studies have rather unexpectedly shown that the GABAergic and metabolic activities of the external pallidum are not decreased in human and non-human primates with Parkinsonism. This absence of any decrease in activity might be explained by the functionally antagonistic influences of the striatal and subthalamic afferences within the external pallidum, as suggested by several anatomical studies. In addition, there are clues from electrophysiological studies to suggest that the hyperactivity found in the subthalamic neurons in Parkinsonism may not depend solely on the level of activity in the external pallidum. In such a framework, the hyperactivity of the subthalamic neurons would have to be explained, at least in part, by other sources of excitation or disinhibition. However, any explanation for the origin of the subthalamic overactivity in Parkinsonism remains speculative.

What are the computations of the cerebellum, the basal ganglia and the cerebral cortex?

K Doya — 2007-12-19T20:24:13-00:00

Neural Networks, Vol. 12, No. 7-8. (11 October 1999), pp. 961-974.

The classical notion that the cerebellum and the basal ganglia are dedicated to motor control is under dispute given increasing evidence of their involvement in non-motor functions. Is it then impossible to characterize the functions of the cerebellum, the basal ganglia and the cerebral cortex in a simplistic manner? This paper presents a novel view that their computational roles can be characterized not by asking what are the "goals" of their computation, such as motor or sensory, but by asking what are the "methods" of their computation, specifically, their learning algorithms. There is currently enough anatomical, physiological, and theoretical evidence to support the hypotheses that the cerebellum is a specialized organism for supervised learning, the basal ganglia are for reinforcement learning, and the cerebral cortex is for unsupervised learning. This paper investigates how the learning modules specialized for these three kinds of learning can be assembled into goal-oriented behaving systems. In general, supervised learning modules in the cerebellum can be utilized as "internal models" of the environment. Reinforcement learning modules in the basal ganglia enable action selection by an "evaluation" of environmental states. Unsupervised learning modules in the cerebral cortex can provide statistically efficient representation of the states of the environment and the behaving system. Two basic action selection architectures are shown, namely, reactive action selection and predictive action selection. They can be implemented within the anatomical constraint of the network linking these structures. Furthermore, the use of the cerebellar supervised learning modules for state estimation, behavioral simulation, and encapsulation of learned skill is considered. Finally, the usefulness of such theoretical frameworks in interpreting brain imaging data is demonstrated in the paradigm of procedural learning.

Dynamic Dopamine Modulation in the Basal Ganglia: A Neurocomputational Account of Cognitive Deficits in Medicated and Nonmedicated Parkinsonism

Michael Frank — 2006-01-05T13:43:21-00:00

J. Cogn. Neurosci., Vol. 17, No. 1. (1 January 2005), pp. 51-72.

Dopamine (DA) depletion in the basal ganglia (BG) of Parkinson's patients gives rise to both frontal-like and implicit learning impairments. Dopaminergic medication alleviates some cognitive deficits but impairs those that depend on intact areas of the BG, apparently due to DA "overdose." These findings are difficult to accommodate with verbal theories of BG/DA function, owing to complexity of system dynamics: DA dynamically modulates function in the BG, which is itself a modulatory system. This article presents a neural network model that instantiates key biological properties and provides insight into the underlying role of DA in the BG during learning and execution of cognitive tasks. Specifically, the BG modulates the execution of "actions" (e.g., motor responses and working memory updating) being considered in different parts of the frontal cortex. Phasic changes in DA, which occur during error feedback, dynamically modulate the BG threshold for facilitating/suppressing a cortical command in response to particular stimuli. Reduced dynamic range of DA explains Parkinson and DA overdose deficits with a single underlying dysfunction, despite overall differences in raw DA levels. Simulated Parkinsonism and medication effects provide a theoretical basis for behavioral data in probabilistic classification and reversal tasks. The model also provides novel testable predictions for neuropsychological and pharmacological studies, and motivates further investigation of BG/DA interactions with the prefrontal cortex in working memory.

The neurobiology of visual-saccadic decision making.

PW Glimcher — 2005-02-22T21:47:46-00:00

Annu Rev Neurosci, Vol. 26 (2003), pp. 133-179.

Over the past two decades significant progress has been made toward understanding the neural basis of primate decision making, the biological process that combines sensory data with stored information to select and execute behavioral responses. The most striking progress in this area has been made in studies of visual-saccadic decision making, a system that is becoming a model for understanding decision making in general. In this system, theoretical models of efficient decision making developed in the social sciences are beginning to be used to describe the computations the brain must perform when it connects sensation and action. Guided in part by these economic models, neurophysiologists have been able to describe neuronal activity recorded from the brains of awake-behaving primates during actual decision making. These recent studies have examined the neural basis of decisions, ranging from those made in predictable sensorimotor tasks to those unpredictable decisions made when animals are engaged in strategic conflict. All of these experiments seem to describe a surprisingly well-integrated set of physiological mechanisms that can account for a broad range of behavioral phenomena. This review presents many of these recent studies within the emerging neuroeconomic framework for understanding primate decision making.

The basal ganglia and disorders of movement: Pathophysiological mechanisms

JA Obeso — 2008-02-22T11:03:16-00:00

News Physiol. Sci., Vol. 17, No. APR.. (2002), pp. 51-55.

The basal ganglia are part of a neuronal network organized in parallel circuits. The "motor circuit" is most relevant to the pathophysiology of movement. Abnormal increment or reduction in the inhibitory output activity of basal ganglia give rise, respectively, to poverty and slowness of movement (i.e., Parkinson's disease) or dyskinesias.

Functional and pathophysiological models of the basal ganglia.

T Wichmann — 2008-03-02T05:01:52-00:00

Curr Opin Neurobiol, Vol. 6, No. 6. (December 1996), pp. 751-758.

Because of new data, anatomical and functional models of the basal ganglia in normal and pathological conditions (e.g. Parkinson's and Huntington's diseases) have recently come under greater scrutiny. An update of these models is clearly timely, taking into consideration not only changes in neuronal discharge rates, but also changes in the patterning and synchronization of neuronal discharge, the role of extrastriatal dopamine, and expanded intrinsic and input/output connections of these nuclei.

Reward-predicting activity of dopamine and caudate neurons--a possible mechanism of motivational control of saccadic eye movement.

R Kawagoe — 2005-08-01T15:57:23-00:00

J Neurophysiol, Vol. 91, No. 2. (February 2004), pp. 1013-1024.

Recent studies have suggested that the basal ganglia are related to motivational control of behavior. To study how motivational signals modulate motor signals in the basal ganglia, we examined activity of midbrain dopamine (DA) neurons and caudate (CD) projection neurons while monkeys were performing a one-direction-rewarded version (1DR) of memory-guided saccade task. The cue stimulus indicated the goal position for an upcoming saccade and the presence or absence of reward after the trial. Among four monkeys we studied, three were sensitive to reward such that saccade velocity was significantly higher in the rewarded trials than in the nonrewarded trials; one monkey was insensitive to reward. In the reward-sensitive monkeys, both DA and CD neurons responded differentially to reward-indicating and no-reward-indicating cues. Thus DA neurons responded with excitation to a reward-indicating cue and with inhibition to a no-reward-indicating cue. A group of CD neurons responded to the cue in their response fields (mostly contralateral) and the cue response was usually enhanced when it indicated reward. In the reward-insensitive monkey, DA neurons showed no response to the cue, while the cue responses of CD neurons were not modulated by reward. Many CD neurons in the reward-sensitive monkeys, but not the reward-insensitive monkey, showed precue activity. These results suggest that DA neurons, with their connection to CD neurons, modulate the spatially selective signals in CD neurons in the reward-predicting manner and CD neurons in turn modulate saccade parameters with their polysynaptic connections to the oculomotor brain stem.

Language Control in the Bilingual Brain

J Crinion — 2006-06-10T15:37:19-00:00

Science, Vol. 312, No. 5779. (9 June 2006), pp. 1537-1540.

How does the bilingual brain distinguish and control which language is in use? Previous functional imaging experiments have not been able to answer this question because proficient bilinguals activate the same brain regions irrespective of the language being tested. Here, we reveal that neuronal responses within the left caudate are sensitive to changes in the language or the meaning of words. By demonstrating this effect in populations of German-English and Japanese-English bilinguals, we suggest that the left caudate plays a universal role in monitoring and controlling the language in use. 10.1126/science.1127761

The role of the basal ganglia in habit formation

Henry Yin — 2006-05-20T11:27:51-00:00

Nature Reviews Neuroscience, Vol. 7, No. 6., pp. 464-476.

Vocal experimentation in the juvenile songbird requires a basal ganglia circuit.

BP Olveczky — 2008-06-17T20:22:11-00:00

PLoS biology, Vol. 3, No. 5. (May 2005)

Songbirds learn their songs by trial-and-error experimentation, producing highly variable vocal output as juveniles. By comparing their own sounds to the song of a tutor, young songbirds gradually converge to a stable song that can be a remarkably good copy of the tutor song. Here we show that vocal variability in the learning songbird is induced by a basal-ganglia-related circuit, the output of which projects to the motor pathway via the lateral magnocellular nucleus of the nidopallium (LMAN). We found that pharmacological inactivation of LMAN dramatically reduced acoustic and sequence variability in the songs of juvenile zebra finches, doing so in a rapid and reversible manner. In addition, recordings from LMAN neurons projecting to the motor pathway revealed highly variable spiking activity across song renditions, showing that LMAN may act as a source of variability. Lastly, pharmacological blockade of synaptic inputs from LMAN to its target premotor area also reduced song variability. Our results establish that, in the juvenile songbird, the exploratory motor behavior required to learn a complex motor sequence is dependent on a dedicated neural circuit homologous to cortico-basal ganglia circuits in mammals.

Eye position and memory saccade related responses in substantia nigra pars reticulata.

HM Bayer — 2005-02-22T21:47:22-00:00

Exp Brain Res, Vol. 154, No. 4. (February 2004), pp. 428-441.

The substantia nigra pars reticulata (SNr), a major output nucleus of the basal ganglia, has been implicated anatomically, pharmacologically and physiologically in the generation of saccadic eye movements. However, the unique contribution of the SNr to saccade generation remains elusive. We studied the activity of SNr neurons while rhesus monkeys made saccades from different initial orbital positions, to determine what effects, if any, eye position had on SNr neuronal activity. We found that there was no effect of eye position on SNr neuronal responses. We also examined the responses of SNr neurons during memory-guided saccades to determine whether SNr discharges were affected by whether the target of the upcoming saccade was visible. We found that there was no change in response properties during memory saccade trials as compared to otherwise identical visually guided trials. SNr neurons appear to carry no information about either eye position or whether a movement is guided by a visible or remembered target. These results suggest that nigral signals are encoded in the same coordinate frame as those in the SC and FEF, but that unlike neuronal responses in these areas, SNr activity is not influenced by whether the saccade target remains visible until the movement is executed.

Patterns of bidirectional communication between cortex and basal ganglia during movement in patients with Parkinson disease.

E Lalo — 2008-03-24T15:11:13-00:00

J Neurosci, Vol. 28, No. 12. (19 March 2008), pp. 3008-3016.

Cortico-basal ganglia networks are considered to comprise several parallel and mostly segregated loops, where segregation is achieved in space through topographic connectivity. Recently, it has been suggested that functional segregation may also be achieved in the frequency domain, by selective coupling of related activities at different frequencies. So far, however, any coupling across frequency in the human has only been modeled in terms of unidirectional influences, a misplaced assumption given the looped architecture of the basal ganglia, and has been considered in static terms. Here, we investigate the pattern of bidirectional coupling between mesial and lateral cortical areas and the subthalamic nucleus (STN) at rest and during movement, with and without pharmacological dopaminergic input, in patients with Parkinson's disease. We simultaneously recorded scalp electroencephalographic activity and local field potentials from depth electrodes and deduced patterns of directed coherence between cortical and STN levels across three frequency bands [sub-beta (3-13 Hz), beta (14-35 Hz), gamma (65-90 Hz)] in the different states. Our results show (1) asymmetric bidirectional coupling between STN and both mesial and lateral cortical areas with greater drives from cortex to STN at frequencies <35 Hz, (2) a drop of beta band coupling driven from mesial cortex to STN during movement, and (3) an increase in symmetrical bidirectional drives between STN and mesial cortex and in lateral cortical drive to STN in the gamma band after dopaminergic therapy. The results confirm a bidirectional pattern of cortico-basal ganglia communication that is differentially patterned across frequency bands and changes with movement and dopaminergic input.

Neural correlates of encoding and expression in implicit sequence learning.

RD Seidler — 2005-10-07T16:50:20-00:00

Exp Brain Res, Vol. 165, No. 1. (August 2005), pp. 114-124.

In the domain of motor learning it has been difficult to separate the neural substrate of encoding from that of change in performance. Consequently, it has not been clear whether motor effector areas participate in learning or merely modulate changes in performance. Here, using a variant of the serial reaction time task that dissociated these two factors, we report that encoding during procedural motor learning does engage cortical motor areas and can be characterized by distinct early and late encoding phases. The highest correlation between activation and subsequent changes in motor performance was seen in the motor cortex during early encoding, and in the basal ganglia during the late encoding phase. Our results show that rapid encoding during procedural motor learning involves several distinct processes, and is represented primarily within motor system structures.

Activity of striatal neurons reflects dynamic encoding and recoding of procedural memories

Terra Barnes — 2005-10-20T02:51:21-00:00

Nature, Vol. 437, No. 7062. (20 October 2005), pp. 1158-1161.

Learning to perform a behavioural procedure as a well-ingrained habit requires extensive repetition of the behavioural sequence, and learning not to perform such behaviours is notoriously difficult. Yet regaining a habit can occur quickly, with even one or a few exposures to cues previously triggering the behaviour. To identify neural mechanisms that might underlie such learning dynamics, we made long-term recordings from multiple neurons in the sensorimotor striatum, a basal ganglia structure implicated in habit formation, in rats successively trained on a reward-based procedural task, given extinction training and then given reacquisition training. The spike activity of striatal output neurons, nodal points in cortico-basal ganglia circuits, changed markedly across multiple dimensions during each of these phases of learning. First, new patterns of task-related ensemble firing successively formed, reversed and then re-emerged. Second, task-irrelevant firing was suppressed, then rebounded, and then was suppressed again. These changing spike activity patterns were highly correlated with changes in behavioural performance. We propose that these changes in task representation in cortico-basal ganglia circuits represent neural equivalents of the explore-exploit behaviour characteristic of habit learning.

Computational models of the basal ganglia

Andrew Gillies — 2006-11-02T11:17:48-00:00

Movement Disorders, Vol. 15, No. 5. (2000), pp. 762-770.

Computer simulation studies and mathematical analysis of models of the basal ganglia are being used increasingly to explore theories of basal ganglia function. We review the implications of these new models for a general understanding of basal ganglia function in normal as well as in diseased brains. The focus is on their functional similarities rather than on the details of mathematical methodologies and simulation techniques. Most of the models suggest a vital role for the basal ganglia in learning. Although this interest in learning is partly driven by experimental results associating the acute firing of dopamine cells with reward prediction in monkeys, some of the models have preceded the electrophysiological results. An- other common theme of the models is selection. In this case, the striatum is seen as detecting and selecting cortical contexts for access to basal ganglia output. Although the behavioral consequences of this selection are hard to define, the models provide frameworks within which to explore these ideas empirically. This provides a means of refining our understanding of basal ganglia function and to consider dysfunction within the new logical frameworks.

Emergent Basal Ganglia Pathology within Computational Models

Bradley Voytek — 2006-11-30T16:20:25-00:00

J. Neurosci., Vol. 26, No. 28. (12 July 2006), pp. 7317-7318.

10.1523/JNEUROSCI.2255-06.2006

Hold your horses: A dynamic computational role for the subthalamic nucleus in decision making.

Michael J Frank — 2006-09-28T18:04:56-00:00

Neural Netw (29 August 2006)

The basal ganglia (BG) coordinate decision making processes by facilitating adaptive frontal motor commands while suppressing others. In previous work, neural network simulations accounted for response selection deficits associated with BG dopamine depletion in Parkinson's disease. Novel predictions from this model have been subsequently confirmed in Parkinson patients and in healthy participants under pharmacological challenge. Nevertheless, one clear limitation of that model is in its omission of the subthalamic nucleus (STN), a key BG structure that participates in both motor and cognitive processes. The present model incorporates the STN and shows that by modulating when a response is executed, the STN reduces premature responding and therefore has substantial effects on which response is ultimately selected, particularly when there are multiple competing responses. Increased cortical response conflict leads to dynamic adjustments in response thresholds via cortico-subthalamic-pallidal pathways. The model accurately captures the dynamics of activity in various BG areas during response selection. Simulated dopamine depletion results in emergent oscillatory activity in BG structures, which has been linked with Parkinson's tremor. Finally, the model accounts for the beneficial effects of STN lesions on these oscillations, but suggests that this benefit may come at the expense of impaired decision making.

The thalamostriatal system: a highly specific network of the basal ganglia circuitry.

Y Smith — 2005-06-15T14:17:39-00:00

Trends Neurosci, Vol. 27, No. 9. (September 2004), pp. 520-527.

Although the existence of thalamostriatal projections has long been known, the role(s) of this system in the basal ganglia circuitry remains poorly characterized. The intralaminar and ventral motor nuclei are the main sources of thalamic inputs to the striatum. This review emphasizes the high degree of anatomical and functional specificity of basal ganglia-thalamostriatal projections and discusses various aspects of the synaptic connectivity and neurochemical features that differentiate this glutamate system from the corticostriatal network. It also discusses the importance of thalamostriatal projections from the caudal intralaminar nuclei in the process of attentional orientation. A major task of future studies is to characterize the role(s) of corticostriatal and thalamostriatal pathways in regulating basal ganglia activity in normal and pathological conditions.

Models of the subthalamic nucleus. The importance of intranuclear connectivity.

A Gillies — 2006-11-30T16:29:49-00:00

Med Eng Phys, Vol. 26, No. 9. (November 2004), pp. 723-732.

A coherent set of models is presented that provide novel and testable predictions about the functional role of the subthalamic nucleus (STN) in the basal ganglia. The STN is emerging as an important target for novel therapeutic strategies for the alleviation of Parkinsonian type symptoms [Lancet 345 (1995) 91; Science 249 (1990) 1436]. Computational and mathematical models based on the properties of the STN and its interactions are reviewed. These models focus on core anatomical and physiological data that span many levels. By assessing models of anatomy, dynamic network models, and a detailed model of a recent pharmacological experiment, we can expose the primary modes of STN function and highlight their underlying properties. We show that the presence of functional interactions between STN projection neurons is critical in defining its behaviour and how it interacts with other basal ganglia nuclei. Pulses or switch-like activity patterns emerge in the models as a consequence of these local interactions. Furthermore, the models demonstrate that this behaviour can break down under abnormal conditions resulting in low frequency bursting oscillations. Such oscillations may play a role in symptoms of Parkinson's disease.

Basal Ganglia Functional Connectivity Based on a Meta-Analysis of 126 Positron Emission Tomography and Functional Magnetic Resonance Imaging Publications

Ronald Postuma — 2006-09-01T19:02:45-00:00

Cereb. Cortex, Vol. 16, No. 10. (1 October 2006), pp. 1508-1521.

The striatum receives projections from the entire cerebral cortex. Different, but not mutually exclusive, models of corticostriatal connectivity have been proposed, including connectivity based on proximity, parallel loops, and a model of a tripartite division of the striatum into motor, associative, and limbic areas. All these models were largely based on studies of anatomic connectivity in nonhuman mammals and lesion studies in animals and humans. Functional neuroimaging has the potential to discern patterns of functional connectivity in humans in vivo. We analyzed the functional connectivity between the cortex and the striatum in a meta-analysis of 126 published functional neuroimaging studies. We mapped the peak activations listed in each publication into stereotaxic space and used standard functional imaging statistical methods to determine which cortical areas were most likely to coactivate with different parts of the striatum. The patterns of functional connectivity between the cortex and the different striatal nuclei are broadly consistent with the predictions of the parallel loop model. The rostrocaudal and dorsoventral patterns of corticostriatal functional connectivity are consistent with the tripartite division of the striatum into motor, associative, and limbic zones. 10.1093/cercor/bhj088

Regulation of firing of dopaminergic neurons and control of goal-directed behaviors

Anthony Grace — 2007-04-04T14:05:09-00:00

Trends in Neurosciences, Vol. In Press, Corrected Proof

There are several brain regions that have been implicated in the control of motivated behavior and whose disruption leads to the pathophysiology observed in major psychiatric disorders. These systems include the ventral hippocampus, which is involved in context and focus on tasks, the amygdala, which mediates emotional behavior, and the prefrontal cortex, which modulates activity throughout the limbic system to enable behavioral flexibility. Each of these systems has overlapping projections to the nucleus accumbens, where these inputs are integrated under the modulatory influence of dopamine. Here, we provide a systems-oriented approach to interpreting the function of the dopamine system, its modulation of limbic-cortical interactions and how disruptions within this system might underlie the pathophysiology of schizophrenia and drug abuse.

Interactions between frontal cortex and basal ganglia in working memory: a computational model.

MJ Frank — 2006-02-12T07:11:57-00:00

Cogn Affect Behav Neurosci, Vol. 1, No. 2. (June 2001), pp. 137-160.

The frontal cortex and the basal ganglia interact via a relatively well understood and elaborate system of interconnections. In the context of motor function, these interconnections can be understood as disinhibiting, or "releasing the brakes," on frontal motor action plans: The basal ganglia detect appropriate contexts for performing motor actions and enable the frontal cortex to execute such actions at the appropriate time. We build on this idea in the domain of working memory through the use of computational neural network models of this circuit. In our model, the frontal cortex exhibits robust active maintenance, whereas the basal ganglia contribute a selective, dynamic gating function that enables frontal memory representations to be rapidly updated in a task-relevant manner. We apply the model to a novel version of the continuous performance task that requires subroutine-like selective working memory updating and compare and contrast our model with other existing models and theories of frontal-cortex-basal-ganglia interactions.

Separate neural substrates for skill learning and performance in the ventral and dorsal striatum

Hisham Atallah — 2006-12-26T08:29:05-00:00

Nature Neuroscience, Vol. 10, No. 1. (24 December 2006), pp. 126-131.

Basal-ganglia 'projections' to the prefrontal cortex of the primate.

FA Middleton — 2006-12-04T12:03:54-00:00

Cereb Cortex, Vol. 12, No. 9. (September 2002), pp. 926-935.

We used retrograde transneuronal transport of the McIntyre-B strain of herpes simplex virus type 1 to examine the extent and organization of basal-ganglia-thalamocortical projections to five regions of prefrontal cortex in the cebus monkey (Cebus apella): medial and lateral area 9 (9m and 9l), dorsal and ventral area 46 (46d and 46v) and lateral area 12 (12l). All of these prefrontal areas were found to be targets of basal-ganglia output that originated in the internal segment of the globus pallidus (GPi) and/or the pars reticulata of the substantia nigra (SNpr). Approximately one-third of the total volume of these nuclei was directed toward prefrontal cortex, a volume comparable to that directed at the cortical motor areas. The origins of the outputs to different prefrontal areas were topographically organized. Different portions of SNpr (the rostral and caudal thirds) projected to areas 9m and 12l. Similarly, different output nuclei (GPi and SNpr) projected to adjacent portions of the same cytoarchitectonic field (46d and 46v). Furthermore, the outputs to prefrontal areas were segregated from those to motor areas of cortex. Thus, basal-ganglia outputs to prefrontal cortex are both extensive and topographically organized, forming a rich anatomical substrate for basal-ganglia influences on the cognitive operations of the frontal lobe.

DARPP-32: an integrator of neurotransmission.

P Svenningsson — 2007-06-11T16:14:28-00:00

Annu Rev Pharmacol Toxicol, Vol. 44 (2004), pp. 269-296.

Dopamine- and cAMP-regulated phosphoprotein, Mr 32 kDa (DARPP-32), was identified initially as a major target for dopamine and protein kinase A (PKA) in striatum. However, recent advances now indicate that regulation of the state of DARPP-32 phosphorylation provides a mechanism for integrating information arriving at dopaminoceptive neurons, in multiple brain regions, via a variety of neurotransmitters, neuromodulators, neuropeptides, and steroid hormones. Activation of PKA or PKG stimulates DARPP-32 phosphorylation at Thr34 and thereby converts DARPP-32 into a potent inhibitor of protein phosphatase-1 (PP-1). DARPP-32 is also phosphorylated at Thr75 by Cdk5 and this converts DARPP-32 into an inhibitor of PKA. Thus, DARPP-32 has the unique property of being a dual-function protein, acting either as an inhibitor of PP-1 or of PKA. The state of phosphorylation of DARPP-32 at Thr34 depends on the phosphorylation state of two serine residues, Ser102 and Ser137, which are phosphorylated by CK2 and CK1, respectively. By virtue of its ability to modulate the activity of PP-1 and PKA, DARPP-32 is critically involved in regulating electrophysiological, transcriptional, and behavioral responses to physiological and pharmacological stimuli, including antidepressants, neuroleptics, and drugs of abuse.

Competition between feedback loops underlies normal and pathological dynamics in the basal ganglia.

A Leblois — 2006-12-01T11:17:11-00:00

J Neurosci, Vol. 26, No. 13. (29 March 2006), pp. 3567-3583.

Experiments performed in normal animals suggest that the basal ganglia (BG) are crucial in motor program selection. BG are also involved in movement disorders. In particular, BG neuronal activity in parkinsonian animals and patients is more oscillatory and more synchronous than in normal individuals. We propose a new model for the function and dysfunction of the motor part of BG. We hypothesize that the striatum, the subthalamic nucleus, the internal pallidum (GPi), the thalamus, and the cortex are involved in closed feedback loops. The direct (cortex-striatum-GPi-thalamus-cortex) and the hyperdirect loops (cortex-subthalamic nucleus-GPi-thalamus-cortex), which have different polarities, play a key role in the model. We show that the competition between these two loops provides the BG-cortex system with the ability to perform motor program selection. Under the assumption that dopamine potentiates corticostriatal synaptic transmission, we demonstrate that, in our model, moderate dopamine depletion leads to a complete loss of action selection ability. High depletion can lead to synchronous oscillations. These modifications of the network dynamical state stem from an imbalance between the feedback in the direct and hyperdirect loops when dopamine is depleted. Our model predicts that the loss of selection ability occurs before the appearance of oscillations, suggesting that Parkinson's disease motor impairments are not directly related to abnormal oscillatory activity. Another major prediction of our model is that synchronous oscillations driven by the hyperdirect loop appear in BG after inactivation of the striatum.

Cortico–basal ganglia circuit mechanism for a decision threshold in reaction time tasks

Chung-Chuan Lo — 2006-06-28T17:36:05-00:00

Nature Neuroscience, Vol. 9, No. 7. (11 June 2006), pp. 956-963.

Time-varying covariance of neural activities recorded in striatum and frontal cortex as monkeys perform sequential-saccade tasks.

N Fujii — 2006-12-04T11:37:53-00:00

Proc Natl Acad Sci U S A, Vol. 102, No. 25. (21 June 2005), pp. 9032-9037.

Cortico-basal ganglia circuits are key parts of the brain's habit system, but little is yet known about how these forebrain pathways function as ingrained habits are performed. We simultaneously recorded spike and local field potential (LFP) activity from regions of the frontal cortex and basal ganglia implicated in visuo-oculomotor control as highly trained macaque monkeys performed sequences of visually guided saccades. The tasks were repetitive, required no new learning, and could be performed nearly automatically. Our findings demonstrate striking differences between the relative timing of striatal and cortical activity during performance of the tasks. At the onset of the visual cues, LFPs in the prefrontal cortex and the oculomotor zone of the striatum showed near-synchronous activation. During the period of sequential-saccade performance, however, peak LFP activity occurred 100-300 msec later in the striatum than in the prefrontal cortex. Peak prefrontal activity tended to be peri-saccadic, whereas peak striatal activity tended to be post-saccadic. This temporal offset was also apparent in pairs of simultaneously recorded prefrontal and striatal neurons. In triple-site recordings, the LFP activity recorded in the supplementary eye field shared temporal characteristics of both the prefrontal and the striatal patterns. The near simultaneity of prefrontal and striatal peak responses at cue onsets, but temporal lag of striatal activity in the movement periods, suggests that the striatum may integrate corollary discharge or confirmatory response signals during sequential task performance. These timing relationships may be signatures of the normal functioning of striatal and frontal cortex during repetitive performance of learned behaviors.

The basal ganglia: learning new tricks and loving it.

AM Graybiel — 2006-02-06T19:49:44-00:00

Curr Opin Neurobiol, Vol. 15, No. 6. (December 2005), pp. 638-644.

The field of basal ganglia research is exploding on every level - from discoveries at the molecular level to those based on human brain imaging. A remarkable series of new findings support the view that the basal ganglia are essential for some forms of learning-related plasticity. Other new findings are challenging some of the basic tenets of the field as it now stands. Combined with the new evidence on learning-related functions of the basal ganglia, these studies suggest that the basal ganglia are parts of a brain-wide set of adaptive neural systems promoting optimal motor and cognitive control.

Functional anatomy of the basal ganglia.

J Yelnik — 2006-11-30T16:36:10-00:00

Mov Disord, Vol. 17 Suppl 3 (2002)

Four organizational levels of the basal ganglia that could be particularly determinant in terms of functional properties are reviewed: (1) macroscopic anatomy, which is characterized by a dramatic decrease of cerebral tissue volume from the cerebral cortex to the deepest portions of the basal ganglia; (2) connectivity, which consists of both complex loops and a partition into three territories, sensorimotor, associative, and limbic (which process motor, cognitive, and emotional information, respectively); (3) neuronal morphology, characterized by a dramatic numeric and geometric convergence of striatal neurons onto pallidonigral neurons; and (4) dopaminergic innervation of the basal ganglia, which is organized as a dual system that is supposed to have opposite effects on the activity of the system. Current models of the basal ganglia are discussed.

Dopaminergic Mechanisms in Actions and Habits

Jeffery Wickens — 2007-08-03T09:40:10-00:00

J. Neurosci., Vol. 27, No. 31. (1 August 2007), pp. 8181-8183.

Recent studies suggest new ways to interpret dopaminergic actions in goal-directed performance and habitual responding. In the early stages of learning dopamine plays an essential role, but with extended training dopamine appears to play a decreasing role in response expression. Experimental manipulation of dopamine levels alters the correlation of cortical and striatal neural activity in behaving animals, and these dopamine-dependent changes in corticostriatal correlations may be reflected in changes in action selection in the basal ganglia. Consistent with this hypothesis, changes in dopamine signaling brought about by sensitization with amphetamine mimic the transition from goal-directed to habit-based instrumental performance. At the cellular level, dopamine-dependent synaptic plasticity may be important initially, and subsequently lead to more persistent changes that no longer require dopamine. The locus of these actions within the cortical and corticostriatal circuitry is a focus on ongoing research. 10.1523/JNEUROSCI.1671-07.2007

Modulation of striatal single units by expected reward: a spiny neuron model displaying dopamine-induced bistability.

AJ Gruber — 2006-11-23T12:37:41-00:00

J Neurophysiol, Vol. 90, No. 2. (August 2003), pp. 1095-1114.

Single-unit activity in the neostriatum of awake monkeys shows a marked dependence on expected reward. Responses to visual cues differ when animals expect primary reinforcements, such as juice rewards, in comparison to secondary reinforcements, such as tones. The mechanism of this reward-dependent modulation has not been established experimentally. To assess the hypothesis that direct neuromodulatory effects of dopamine on spiny neurons can account for this modulation, we develop a computational model based on simplified representations of key ionic currents and their modulation by D1 dopamine receptor activation. This minimal model can be analyzed in detail. We find that D1-mediated increases of inward rectifying potassium and L-type calcium currents cause a bifurcation: the native up/down state behavior of the spiny neuron model becomes truly bistable, which modulates the peak firing rate and the duration of the up state and introduces a dependence of the response on the past state history. These generic consequences of dopamine neuromodulation through bistability can account for both reward-dependent enhancement and suppression of spiny neuron single-unit responses to visual cues. We validate the model by simulating responses to visual targets in a memory-guided saccade task; our results are in close agreement with the main features of the experimental data. Our model provides a conceptual framework for understanding the functional significance of the short-term neuromodulatory actions of dopamine on signal processing in the striatum.

Dopamine modulation in the basal ganglia locks the gate to working memory.

AJ Gruber — 2006-11-21T13:36:48-00:00

J Comput Neurosci, Vol. 20, No. 2. (April 2006), pp. 153-166.

The prefrontal cortex and basal ganglia are deeply implicated in working memory. Both structures are subject to dopaminergic neuromodulation in a way that exerts a critical influence on the proper operation of working memory. We present a novel network model to elucidate the role of phasic dopamine in the interaction of these two structures in initiating and maintaining mnemonic activity. We argue that neuromodulation plays a critical role in protecting memories against both internal and external sources of noise. Increases in cortical gain engendered by prefrontal dopamine release help make memories robust against external distraction, but do not offer protection against internal noise accompanying recurrent cortical activity. Rather, the output of the basal ganglia provides the gating function of stabilization against noise and distraction by enhancing select memories through targeted disinhibition of cortex. Dopamine in the basal ganglia effectively locks this gate by influencing the stability of up and down states in the striatum. Dopamine's involvement in affective processing endows this gating with specificity to motivational salience. We model a spatial working memory task and show that these combined effects of dopamine lead to superior performance.

Network models of the basal ganglia.

DG Beiser — 2006-11-23T12:34:21-00:00

Curr Opin Neurobiol, Vol. 7, No. 2. (April 1997), pp. 185-190.

Over the past year, a number of conceptual and mathematical models of the basal ganglia and their interactions with other areas of the brain have appeared in the literature. Even though the models each differ in significant ways, several computational principles, such as convergence, recurrence and competition, appear to have emerged as common themes of information processing in the basal ganglia. Simulation studies of these models have provoked new types of questions at the many levels of inquiry linking biophysics to behavior.

Model of Cortical-Basal Ganglionic Processing: Encoding the Serial Order of Sensory Events

David Beiser — 2006-06-06T00:26:56-00:00

J Neurophysiol, Vol. 79, No. 6. (1 June 1998), pp. 3168-3188.

Mesocortical dopamine modulation of executive functions: beyond working memory.

SB Floresco — 2006-12-04T12:36:22-00:00

Psychopharmacology (Berl), Vol. 188, No. 4. (November 2006), pp. 567-585.

RATIONALE: Dopamine (DA) neurotransmission in the prefrontal cortex (PFC) is known to play an essential role in mediating executive functions such as the working memory. DA exerts these effects by acting on D(1) receptors because blockade or stimulation of these receptors in the PFC can impair performance on delayed response tasks. However, comparatively less is known about dopaminergic mechanisms that mediate other executive functions regulated by the PFC. Furthermore, the functional importance of other DA receptor subtypes that reside on PFC neurons (D(2) and D(4)) is unclear. OBJECTIVES: This review will summarize previous findings and previously unpublished data addressing the contribution of PFC DA to higher-order cognition. We will compare the DA receptor mechanisms, which regulate executive functions such as working memory, behavioral flexibility, and decision-making. RESULTS AND CONCLUSIONS: Whereas PFC D(1) receptor activity is of primary importance in working memory, D(1) and D(2) receptors act in a cooperative manner to facilitate behavioral flexibility. We note that the principle of the "inverted U-shaped" function of D(1) receptor activity mediating working memory does not necessarily apply to other PFC functions. DA in different subregions of the PFC also mediates decision-making assessed with delay discounting or effort-based procedures, and we report that D(1), D(2), and D(4) receptors in the medial PFC contribute to decision-making when animals must bias the direction of behavior to avoid aversive stimuli, assessed with a conditioned punishment procedure. Thus, mesocortical DA modulation of distinct executive functions is subserved by dissociable profiles of DA receptor activity in the PFC.