CiteULike: oamg's library [437 articles]

Behavioral Shifts and Action Valuation in the Anterior Cingulate Cortex

Rene Quilodran — 2008-01-24T15:58:11-00:00

Neuron, Vol. 57, No. 2. (24 January 2008), pp. 314-325.

Summary Rapid optimization of behavior requires decisions about when to explore and when to exploit discovered resources. The mechanisms that lead to fast adaptations and their interaction with action valuation are a central issue. We show here that the anterior cingulate cortex (ACC) encodes multiple feedbacks devoted to exploration and its immediate termination. In a task that alternates exploration and exploitation periods, the ACC monitored negative and positive outcomes relevant for different adaptations. In particular, it produced signals specific of the first reward, i.e., the end of exploration. Those signals disappeared in exploitation periods but immediately transferred to the initiation of trials--a transfer comparable to learning phenomena observed for dopaminergic neurons. Importantly, these were also observed for high gamma oscillations of local field potentials shown to correlate with brain imaging signal. Thus, mechanisms of action valuation and monitoring of events/actions are combined for rapid behavioral regulation.

Cooperation and conflict in quorum-sensing bacterial populations

Stephen Diggle — 2007-11-14T23:13:54-00:00

Nature, Vol. 450, No. 7168. (15 November 2007), pp. 411-414.

Evaluation of the Balloon Analogue Risk Task (BART) as a predictor of adolescent real-world risk-taking behaviours

CW Lejuez — 2007-11-05T19:32:51-00:00

Journal of Adolescence, Vol. 26, No. 4. (August 2003), pp. 475-479.

The Balloon Analogue Risk Task (BART) was administered to a sample of 26 high school-aged adolescents to test the utility of the BART as a behavioural measure of risk-taking propensity. Data indicate that riskyness on the BART was related to self-reported engagement in real-world risk-taking behaviours. These data replicate and uniquely extend past research to an adolescent sample, suggesting that the BART may be a useful addition to self-report batteries for the assessment of risk-taking behaviours in adolescents.

Functional Interactions during the Retrieval of Conceptual Action Knowledge: An fMRI Study

Ann Assmus — 2007-11-02T12:54:34-00:00

J. Cogn. Neurosci., Vol. 19, No. 6. (1 June 2007), pp. 1004-1012.

Impaired retrieval of conceptual knowledge for actions has been associated with lesions of left premotor, left parietal, and left middle temporal areas [Tranel, D., Kemmerer, D., Adolphs, R., Damasio, H., & Damasio, A. R. Neural correlates of conceptual knowledge for actions. Cognitive Neuropsychology, 409-432, 2003]. Here we aimed at characterizing the differential contribution of these areas to the retrieval of conceptual knowledge about actions. During functional magnetic resonance imaging (fMRI), different categories of pictograms (whole-body actions, manipulable and nonmanipulable objects) were presented to healthy subjects. fMRI data were analyzed using SPM2. A conjunction analysis of the neural activations elicited by all pictograms revealed (p < .05, corrected) a bilateral inferior occipito-temporal neural network with strong activations in the right and left fusiform gyri. Action pictograms contrasted to object pictograms showed differential activation of area MT+, the inferior and superior parietal cortex, and the premotor cortex bilaterally. An analysis of psycho-physiological interactions identified contribution-dependent changes in the neural responses when pictograms triggered the retrieval of conceptual action knowledge: Processing of action pictograms specifically enhanced the neural interaction between the right and left fusiform gyri, the right and left middle temporal cortices (MT+), and the left superior and inferior parietal cortex. These results complement and extend previous neuropsychological and neuroimaging studies by showing that knowledge about action concepts results from an increased coupling between areas concerned with semantic processing (fusiform gyrus), movement perception (MT+), and temporo-spatial movement control (left parietal cortex).

The neural substrate of human empathy: effects of perspective-taking and cognitive appraisal.

C Lamm — 2007-10-29T20:07:34-00:00

J Cogn Neurosci, Vol. 19, No. 1. (January 2007), pp. 42-58.

Whether observation of distress in others leads to empathic concern and altruistic motivation, or to personal distress and egoistic motivation, seems to depend upon the capacity for self-other differentiation and cognitive appraisal. In this experiment, behavioral measures and event-related functional magnetic resonance imaging were used to investigate the effects of perspective-taking and cognitive appraisal while participants observed the facial expression of pain resulting from medical treatment. Video clips showing the faces of patients were presented either with the instruction to imagine the feelings of the patient ("imagine other") or to imagine oneself to be in the patient's situation ("imagine self"). Cognitive appraisal was manipulated by providing information that the medical treatment had or had not been successful. Behavioral measures demonstrated that perspective-taking and treatment effectiveness instructions affected participants' affective responses to the observed pain. Hemodynamic changes were detected in the insular cortices, anterior medial cingulate cortex (aMCC), amygdala, and in visual areas including the fusiform gyrus. Graded responses related to the perspective-taking instructions were observed in middle insula, aMCC, medial and lateral premotor areas, and selectively in left and right parietal cortices. Treatment effectiveness resulted in signal changes in the perigenual anterior cingulate cortex, in the ventromedial orbito-frontal cortex, in the right lateral middle frontal gyrus, and in the cerebellum. These findings support the view that humans' responses to the pain of others can be modulated by cognitive and motivational processes, which influence whether observing a conspecific in need of help will result in empathic concern, an important instigator for helping behavior.

The Visual What For Area: Words and pictures in the left fusiform gyrus.

R Starrfelt — 2007-03-27T20:01:32-00:00

Neuroimage, Vol. 35, No. 1. (March 2007), pp. 334-342.

An area in the left fusiform gyrus labelled the Visual Word Form Area (VWFA) is claimed to be especially, or even selectively, responsive to words. We explored how stimulus type and task demands affect activity in this area by conducting a PET experiment where words and pictures were presented in two conditions that differed in demands on shape processing: colour decision and categorization. The subjects also performed an object decision task with pictures only. The imaging data revealed a main effect of stimulus type: rCBF was higher during word compared with picture processing. When compared individually for colour decision and categorization, the difference between words and pictures was only significant during colour decision, although a trend was present during categorization also. rCBF in the VWFA was highest during the object decision task, where only pictures were presented. Our findings indicate that the putative VWFA is activated more by written words than pictures, but only under certain circumstances. As demands on shape processing increase, the difference in activation between words and pictures decreases and can even be abolished. We suggest that activation in the VWFA could reflect shape configuration-the integration of shape elements into elaborate shape descriptions corresponding to whole objects or words. This process may be required to different degrees for pictures and words depending on task demands.

Functional interactions during the retrieval of conceptual action knowledge: an fMRI study.

A Assmus — 2007-08-03T16:50:04-00:00

J Cogn Neurosci, Vol. 19, No. 6. (June 2007), pp. 1004-1012.

Impaired retrieval of conceptual knowledge for actions has been associated with lesions of left premotor, left parietal, and left middle temporal areas [Tranel, D., Kemmerer, D., Adolphs, R., Damasio, H., & Damasio, A. R. Neural correlates of conceptual knowledge for actions. Cognitive Neuropsychology, 409-432, 2003]. Here we aimed at characterizing the differential contribution of these areas to the retrieval of conceptual knowledge about actions. During functional magnetic resonance imaging (fMRI), different categories of pictograms (whole-body actions, manipulable and nonmanipulable objects) were presented to healthy subjects. fMRI data were analyzed using SPM2. A conjunction analysis of the neural activations elicited by all pictograms revealed ( p<.05, corrected) a bilateral inferior occipito-temporal neural network with strong activations in the right and left fusiform gyri. Action pictograms contrasted to object pictograms showed differential activation of area MT+, the inferior and superior parietal cortex, and the premotor cortex bilaterally. An analysis of psychophysiological interactions identified contribution-dependent changes in the neural responses when pictograms triggered the retrieval of conceptual action knowledge: Processing of action pictograms specifically enhanced the neural interaction between the right and left fusiform gyri, the right and left middle temporal cortices (MT+), and the left superior and inferior parietal cortex. These results complement and extend previous neuropsychological and neuroimaging studies by showing that knowledge about action concepts results from an increased coupling between areas concerned with semantic processing (fusiform gyrus), movement perception (MT+), and temporospatial movement control (left parietal cortex).

Face processing without awareness in the right fusiform gyrus.

James P Morris — 2007-07-25T00:38:25-00:00

Neuropsychologia (13 June 2007)

We investigated brain activity evoked by faces which were not consciously perceived by subjects. Subdural electrophysiological recordings and functional neuroimaging studies have each demonstrated face-specific processing in the fusiform gyrus (FFG) of humans. Using pattern masks, a stimulus can be presented but not consciously perceived, and thus can be used to assay obligatory or automatic processes. Here, using event-related functional magnetic resonance imaging and pattern masking, we observed that masked faces but not masked objects activated the right FFG. Other regions activated by consciously perceived unmasked faces were not activated when faces were masked. These data provide strong evidence for an automatic face-processing region in the right FFG.

Dorsal striatum responses to reward and punishment: Effects of valence and magnitude manipulations

MR Delgado — 2007-10-24T15:25:39-00:00

pp. 27-38.

The goal of this research was to further our understanding of how the striatum responds to the delivery of affective feedback. Previously, we had found that the striatum showed a pattern of sustained activation after presentation of a monetary reward, in contrast to a decrease in the hemodynamic response after a punishment. In this study, we tested whether the activity of the striatum could be modulated by parametric variations in the amount of financial reward or punishment. We used an event-related fMRI design in which participants received large or small monetary rewards or punishments after performance in a gambling task. A parametric ordering of conditions was observed in the dorsal striatum according to both magnitude and valence. In addition, an early response to the presentation of feedback was observed and replicated in a second experiment with increased temporal resolution. This study further implicates the dorsal striatum as an integral component of a reward circuitry responsible for the control of motivated behavior, serving to code for such feedback properties as valence and magnitude.

Remembering: functional organization of the declarative memory system.

H Eichenbaum — 2007-10-24T14:21:19-00:00

Curr Biol, Vol. 16, No. 16. (22 August 2006)

How do brain systems support our subjective experience of recollection and our senses of familiarity and novelty? A new functional imaging study concludes that each of these functions is accomplished by a distinct component of the medial temporal lobe, shedding new light on the functional organization of this memory system.

Grounding object concepts in perception and action: evidence from fMRI studies of tools.

MS Beauchamp — 2007-10-24T14:05:38-00:00

Cortex, Vol. 43, No. 3. (April 2007), pp. 461-468.

Studies of categories of objects, including tools, have spurred the development of the sensory-motor model of object concept representation. According to this model, information about objects is represented in the same neural subsystems that are active when we perceive and use them. In turn, this model has provided insight into the brain mechanisms of tool use. For tools, three types of information are especially important for identification: the characteristic motion with which they move (such as the up and down motion of a hammer), their visual form, and the way that they are manipulated. Evidence from neuropsychological, non-human primates, and neuroimaging studies suggest a mapping between specific brain regions and these fundamental identifying properties of tools. We focus on neuroimaging studies of the left posterior middle temporal gyrus. This brain region is active both when subjects perceive moving tools and when they answer questions about tools, and is responsive to the type of visual motion characteristic of tools: rigid, unarticulated motion. We describe a simple model that explains how low-level receptive field properties like those known to exist in area MT/V5 could give rise to the high-level category-related representations observed in functional imaging experiments.

Recognition memory and the medial temporal lobe: a new perspective

Larry Squire — 2007-10-20T17:10:56-00:00

Nature Reviews Neuroscience, Vol. 8, No. 11., pp. 872-883.

A network representation of response probability in the striatum.

PM Blazquez — 2006-05-25T12:26:25-00:00

Neuron, Vol. 33, No. 6. (14 March 2002), pp. 973-982.

The striatum of the basal ganglia is considered a key structure in the learning circuitry of the brain. To analyze neural signals that underlie striatal plasticity, we recorded from an identifiable class of striatal interneurons as macaque monkeys underwent training in a range of conditioning and non-associative learning paradigms, and recorded eyeblink electromyographs as the measure of behavioral response. We found that the responses of these striatal interneurons were modifiable under all training conditions and that their population responses were tightly correlated with the probability that a given stimulus would evoke a behavioral response. Such a network signal, proportional to current response probability, could be crucial to the learning and decision functions of the basal ganglia.

Responses to reward in monkey dorsal and ventral striatum.

P Apicella — 2006-01-25T22:59:31-00:00

Exp Brain Res, Vol. 85, No. 3. (1991), pp. 491-500.

The sources of input and the behavioral effects of lesions and drug administration suggest that the striatum participates in motivational processes. We investigated the activity of single striatal neurons of monkeys in response to reward delivered for performing in a go-nogo task. A drop of liquid was given each time the animal correctly executed or withheld an arm movement in reaction to a visual stimulus. Of 1593 neurons, 115 showed increased activity in response to delivery of liquid reward in both go and nogo trials. Responding neurons were predominantly located in dorsal and ventromedial parts of anterior putamen, in dorsal and ventral caudate, and in nucleus accumbens. They were twice as frequent in ventral as compared to dorsal striatal areas. Responses occurred at a median latency of 337 ms and lasted for 525 ms, with insignificant differences between dorsal and ventral striatum. Reward responses differed from activity recorded in the face area of posterior putamen which varied synchronously with individual mouth movements. Responses were directly related to delivery of primary liquid reward and not to auditory stimuli associated with it. Most of them also occurred when reward was delivered outside of the task. These results demonstrate that neurons of dorsal and particularly ventral striatum are involved in processing information concerning the attribution of primary reward.

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

Functions of dopamine in the dorsal and ventral striatum

Trevor Robbins — 2007-10-22T14:02:38-00:00

Seminars in Neuroscience, Vol. 4, No. 2. (April 1992), pp. 119-127.

Manipulations of dopamine levels in the dorsal and ventral striatum are shown to affect the activation of behaviour in distinct, yet parallel ways, which depend upon the nature of the neocortical and limbic input to these structures. Whereas dopamine in the dorsal striatum contributes to the sensorimotor co-ordination of consummatory behaviour and the development of a `response set' in motor preparatory processes for skilled responses, dopamine in the ventral striatum influences the impact of reward-related stimuli on appetitive aspects of behaviour. The circumstances under which the striatal dopamine projections are normally active to effect these functions are defined by studies which attempt to correlate firing in single units or neurochemical indices of dopamine activity with environmental conditions, internal states and behaviour.

Putting a spin on the dorsal-ventral divide of the striatum.

P Voorn — 2006-01-25T02:36:21-00:00

Trends Neurosci, Vol. 27, No. 8. (August 2004), pp. 468-474.

Since its conception three decades ago, the idea that the striatum consists of a dorsal sensorimotor part and a ventral portion processing limbic information has sparked a quest for functional correlates and anatomical characteristics of the striatal divisions. But this classic dorsal-ventral distinction might not offer the best view of striatal function. Anatomy and neurophysiology show that the two striatal areas have the same basic structure and that sharp boundaries are absent. Behaviorally, a distinction between dorsolateral and ventromedial seems most valid, in accordance with a mediolateral functional zonation imposed on the striatum by its excitatory cortical, thalamic and amygdaloid inputs. Therefore, this review presents a synthesis between the dorsal-ventral distinction and the more mediolateral-oriented functional striatal gradient.

Human striatal activation reflects degree of stimulus saliency

Caroline Zink — 2007-10-22T13:51:49-00:00

NeuroImage, Vol. 29, No. 3. (1 February 2006), pp. 977-983.

Salient stimuli are characterized by their capability to perturb and seize available cognitive resources. Although the striatum and its dopaminergic inputs respond to a variety of stimuli categorically defined as salient, including rewards, the relationship between striatal activity and saliency is not well understood. Specifically, it is unclear if the striatum responds in an all-or-none fashion to salient events or instead responds in a graded fashion to the degree of saliency associated with an event. Using functional magnetic resonance imaging, we measured activity in the brains of 20 participants performing a visual classification task in which they identified single digits as odd or even numbers. An auditory tone preceded each number, which was occasionally, and unexpectedly, substituted by a novel sound. The novel sounds varied in their ability to interrupt and reallocate cognitive resources (i.e., their saliency) as measured by a delay in reaction time to immediately subsequent numerical task-stimuli. The present findings demonstrate that striatal activity increases proportionally to the degree to which an unexpected novel sound interferes with the current cognitive focus, even in the absence of reward. These results suggest that activity in the human striatum reflects the level of saliency associated with a stimulus, perhaps providing a signal to reallocate limited resources to important events.

Expectation Modulates Neural Responses to Pleasant and Aversive Stimuli in Primate Amygdala

Marina Belova — 2007-09-20T13:17:19-00:00

Neuron, Vol. 55, No. 6. (20 September 2007), pp. 970-984.

Summary Animals and humans learn to approach and acquire pleasant stimuli and to avoid or defend against aversive ones. However, both pleasant and aversive stimuli can elicit arousal and attention, and their salience or intensity increases when they occur by surprise. Thus, adaptive behavior may require that neural circuits compute both stimulus valence--or value--and intensity. To explore how these computations may be implemented, we examined neural responses in the primate amygdala to unexpected reinforcement during learning. Many amygdala neurons responded differently to reinforcement depending upon whether or not it was expected. In some neurons, this modulation occurred only for rewards or aversive stimuli, but not both. In other neurons, expectation similarly modulated responses to both rewards and punishments. These different neuronal populations may subserve two sorts of processes mediated by the amygdala: those activated by surprising reinforcements of both valences--such as enhanced arousal and attention--and those that are valence-specific, such as fear or reward-seeking behavior.

Encoding Predicted Outcome and Acquired Value in Orbitofrontal Cortex during Cue Sampling Depends upon Input from Basolateral Amygdala

Geoffrey Schoenbaum — 2007-10-18T17:07:56-00:00

Neuron, Vol. 39, No. 5. (28 August 2003), pp. 855-867.

Certain goal-directed behaviors depend critically upon interactions between orbitofrontal cortex (OFC) and basolateral amygdala (ABL). Here we describe direct neurophysiological evidence of this cooperative function. We recorded from OFC in intact and ABL-lesioned rats learning odor discrimination problems. As rats learned these problems, we found that lesioned rats exhibited marked changes in the information represented in OFC during odor cue sampling. Lesioned rats had fewer cue-selective neurons in OFC after learning; the cue-selective population in lesioned rats did not include neurons that were also responsive in anticipation of the predicted outcome; and the cue-activated representations that remained in lesioned rats were less associative and more often bound to cue identity. The results provide a neural substrate for representing acquired value and features of the predicted outcome during cue sampling, disruption of which could account for deficits in goal-directed behavior after damage to this system.

From Thought to Action: The Parietal Cortex as a Bridge between Perception, Action, and Cognition

Jacqueline Gottlieb — 2007-01-11T19:27:59-00:00

Neuron, Vol. 53, No. 1. (4 January 2007), pp. 9-16.

The lateral intraparietal area (LIP) is a subdivision of the inferior parietal lobe that has been implicated in the guidance of spatial attention. In a variety of tasks, LIP provides a "salience representation" of the external world--a topographic visual representation that encodes the locations of salient or behaviorally relevant objects. Recent neurophysiological experiments show that this salience representation incorporates information about multiple behavioral variables--such as a specific motor response, reward, or category membership--associated with the task-relevant object. This integration occurs in a wide variety of tasks, including those requiring eye or limb movements or goal-directed or nontargeting operant responses. Thus, LIP acts as a multifaceted behavioral integrator that binds visuospatial, motor, and cognitive information into a topographically organized signal of behavioral salience. By specifying attentional priority as a synthesis of multiple task demands, LIP operates at the interface of perception, action, and cognition.

Anterior cingulate cortical neuronal activity during perception of noxious thermal stimuli in monkeys.

K Iwata — 2007-08-20T20:25:23-00:00

J Neurophysiol, Vol. 94, No. 3. (September 2005), pp. 1980-1991.

It has been reported that the anterior cingulate cortex (ACC) has a variety of functions relating to pain as well as pain perception. However, the underlying mechanisms for those functions remain unclear. To elucidate the functional role of the ACC in pain perception and pain-related functions such as attention to pain and escape from pain, single neuronal activity was recorded from the ACC, and the behavioral correlates of this neuronal activity was studied. A total of 667 neurons were recorded from the ACC in awake behaving monkeys. Twenty-one had modulated activity during a heat-detection task. Eighteen of these increased their firing frequency following an increase in stimulus temperature, whereas three of them had decreased firing during heating of the face. Seventy-five percent of heat-evoked responses of heat-responsive ACC neurons were significantly depressed when monkeys detected the change in magnitude of illumination of a light presented on the front panel. The neuronal activity was significantly higher when monkeys escaped from a noxious heat stimulus than when the monkeys detected a small change in temperature (T2) above a larger initial shift (T1). No relationship between firing frequency and detection latency of the T2 stimulation was observed. These findings suggest that ACC nociceptive neurons are involved in attention to pain and escape from pain but not in the sensory discriminative aspect of pain.

Neural coding of "attention for action" and "response selection" in primate anterior cingulate cortex.

Y Isomura — 2006-01-20T16:49:41-00:00

J Neurosci, Vol. 23, No. 22. (3 September 2003), pp. 8002-8012.

Noninvasive imaging techniques showed that the anterior cingulate cortex is related to higher-order cognitive and motor-related functions in humans. To elucidate the cellular mechanism of such cingulate functions, single-unit activity was recorded from three cingulate motor areas of macaque monkeys performing delayed conditional Go/No-go discrimination tasks using spatial (location) and nonspatial (color) visual cues. Unlike prefrontal neurons, only a few neurons coded the visual information on individual features (e.g., "left" or "red") in all of the rostral (CMAr), dorsal (CMAd), and ventral (CMAv) cingulate motor areas. Instead, many neurons in the CMAr exhibited the attention-like activity anticipating the second (conditioned) visual cues, with the specificity to visual category ("location" or "color"). In addition, there were a number of CMAr neurons specific to motor response (Go or No-go) in relation to the second visual cues. Some of the visual category-specific neurons in the CMAr further displayed the motor response-specific activity. On the other hand, many of the task-related CMAd and CMAv neurons seemed to be implicated directly in motor functions, such as preparation and execution of movements in Go trials. The present results suggest that the CMAr neurons may participate in cognitive and motor functions of "attention for action" and "response selection" for an appropriate action according to an intention, whereas the CMAd and CMAv neurons may be involved in "motor preparation and execution".

Monotonic coding of numerosity in macaque lateral intraparietal area.

JD Roitman — 2007-08-21T16:20:34-00:00

PLoS Biol, Vol. 5, No. 8. (August 2007)

As any child knows, the first step in counting is summing up individual elements, yet the brain mechanisms responsible for this process remain obscure. Here we show, for the first time, that a population of neurons in the lateral intraparietal area of monkeys encodes the total number of elements within their classical receptive fields in a graded fashion, across a wide range of numerical values (2-32). Moreover, modulation of neuronal activity by visual quantity developed rapidly, within 100 ms of stimulus onset, and was independent of attention, reward expectations, or stimulus attributes such as size, density, or color. The responses of these neurons resemble the outputs of "accumulator neurons" postulated in computational models of number processing. Numerical accumulator neurons may provide inputs to neurons encoding specific cardinal values, such as "4," that have been described in previous work. Our findings may explain the frequent association of visuospatial and numerical deficits following damage to parietal cortex in humans.

Cortico-striatal synaptic defects and OCD-like behaviours in Sapap3-mutant mice

Jeffrey Welch — 2007-08-23T02:52:28-00:00

Nature, Vol. 448, No. 7156. (2007), pp. 894-900.

Intense sweetness surpasses cocaine reward.

M Lenoir — 2007-08-20T20:45:59-00:00

PLoS ONE, Vol. 2 (2007)

BACKGROUND: Refined sugars (e.g., sucrose, fructose) were absent in the diet of most people until very recently in human history. Today overconsumption of diets rich in sugars contributes together with other factors to drive the current obesity epidemic. Overconsumption of sugar-dense foods or beverages is initially motivated by the pleasure of sweet taste and is often compared to drug addiction. Though there are many biological commonalities between sweetened diets and drugs of abuse, the addictive potential of the former relative to the latter is currently unknown. METHODOLOGY/PRINCIPAL FINDINGS: Here we report that when rats were allowed to choose mutually-exclusively between water sweetened with saccharin-an intense calorie-free sweetener-and intravenous cocaine-a highly addictive and harmful substance-the large majority of animals (94%) preferred the sweet taste of saccharin. The preference for saccharin was not attributable to its unnatural ability to induce sweetness without calories because the same preference was also observed with sucrose, a natural sugar. Finally, the preference for saccharin was not surmountable by increasing doses of cocaine and was observed despite either cocaine intoxication, sensitization or intake escalation-the latter being a hallmark of drug addiction. CONCLUSIONS: Our findings clearly demonstrate that intense sweetness can surpass cocaine reward, even in drug-sensitized and -addicted individuals. We speculate that the addictive potential of intense sweetness results from an inborn hypersensitivity to sweet tastants. In most mammals, including rats and humans, sweet receptors evolved in ancestral environments poor in sugars and are thus not adapted to high concentrations of sweet tastants. The supranormal stimulation of these receptors by sugar-rich diets, such as those now widely available in modern societies, would generate a supranormal reward signal in the brain, with the potential to override self-control mechanisms and thus to lead to addiction.

Kalman Filtering : Theory and Practice Using MATLAB

Mohinder Grewal — 2007-08-30T03:42:23-00:00

(16 January 2001)

". . . an authentic magnum opus worth much more than its weight in gold!"-IEEE Transactions on Automatic Control, from a review of the First Edition "The best book I've seen on the subject of Kalman filtering . . . Reading other books on Kalman filters and not this one could make you a very dangerous Kalman filter engineer."-Amazon.com, from a review of the First Edition In this practical introduction to Kalman filtering theory and applications, authors Grewal and Andrews draw upon their decades of experience to offer an in-depth examination of the subtleties, common problems, and limitations of estimation theory as it applies to real-world situations. They provide many illustrative examples drawn from an array of application areas including GPS-aided INS, the modeling of gyros and accelerometers, inertial navigation, and freeway traffic control. In addition, they share many hard-won lessons about, and original methods for, designing, implementing, validating, and improving Kalman filters, including techniques for: * Representing the problem in a mathematical model * Analyzing estimator performance as a function of model parameters * Implementing the mechanization equations in numerically stable algorithms * Assessing computational requirements * Testing the validity of results * Monitoring filter performance in operation As the best way to understand and master a technology is to observe it in action, Kalman Filtering: Theory and Practice Using MATLAB(r), Second Edition includes companion software in MATLAB(r), providing users with an opportunity to experience first hand the filter's workings and its limitations. This updated and revised edition of Grewal and Andrews's classic guide is an indispensable working resource for engineers and computer scientists involved in the design of aerospace and aeronautical systems, global positioning and radar tracking systems, power systems, and biomedical instrumentation. An Instructor's Manual presenting detailed solutions to all the problems in the book is available from the Wiley editorial department.

The Perception of Rational, Goal-Directed Action in Nonhuman Primates

Justin Wood — 2007-09-08T02:28:43-00:00

Science, Vol. 317, No. 5843. (7 September 2007), pp. 1402-1405.

Humans are capable of making inferences about other individuals' intentions and goals by evaluating their actions in relation to the constraints imposed by the environment. This capacity enables humans to go beyond the surface appearance of behavior to draw inferences about an individual's mental states. Presently unclear is whether this capacity is uniquely human or is shared with other animals. We show that cotton-top tamarins, rhesus macaques, and chimpanzees all make spontaneous inferences about a human experimenter's goal by attending to the environmental constraints that guide rational action. These findings rule out simple associative accounts of action perception and show that our capacity to infer rational, goal-directed action likely arose at least as far back as the New World monkeys, some 40 million years ago. 10.1126/science.1144663

Causal inference in multisensory perception.

KP Körding — 2007-09-28T16:43:01-00:00

PLoS ONE, Vol. 2, No. 9. (2007)

Perceptual events derive their significance to an animal from their meaning about the world, that is from the information they carry about their causes. The brain should thus be able to efficiently infer the causes underlying our sensory events. Here we use multisensory cue combination to study causal inference in perception. We formulate an ideal-observer model that infers whether two sensory cues originate from the same location and that also estimates their location(s). This model accurately predicts the nonlinear integration of cues by human subjects in two auditory-visual localization tasks. The results show that indeed humans can efficiently infer the causal structure as well as the location of causes. By combining insights from the study of causal inference with the ideal-observer approach to sensory cue combination, we show that the capacity to infer causal structure is not limited to conscious, high-level cognition; it is also performed continually and effortlessly in perception.

God Is Watching You: Priming God Concepts Increases Prosocial Behavior in an Anonymous Economic Game

Shariff — 2007-08-27T13:19:58-00:00

Psychological Science, Vol. 18, No. 9. (September 2007), pp. 803-809.

The Hemo-Neural Hypothesis: On The Role of Blood Flow in Information Processing.

Christopher Irwin Moore — 2007-10-10T19:18:05-00:00

J Neurophysiol (3 October 2007)

Brain vasculature is a complex and interconnected network under tight regulatory control that exists in intimate communication with neurons and glia. Typically, hemodynamics are considered to exclusively serve as a metabolic support system. In contrast to this canonical view, we propose that hemodynamics also play a role in information processing through modulation of neural activity. Functional hyperemia, the basis of the fMRI BOLD signal, is a localized influx of blood correlated with neural activity levels. Functional hyperemia is considered by many to be excessive from a metabolic standpoint, but may be appropriate if interpreted as having an activity-dependent neuro-modulatory function. Hemodynamics may impact neural activity through direct and indirect mechanisms. Direct mechanisms include delivery of diffusible blood-borne messengers, and mechanical and thermal modulation of neural activity. Indirect mechanisms are proposed to act through hemodynamic modulation of astrocytes, which can in turn regulate neural activity. These hemo-neural mechanisms should alter the information processing capacity of active local neural networks. Here, we focus on analysis of neocortical sensory processing. We predict that hemodynamics alter the gain of local cortical circuits, modulating the detection and discrimination of sensory stimuli. This novel view of information processing, that includes hemodynamics as an active and significant participant, has implications for understanding neural representation and the construction of accurate brain models. There are also potential medical benefits of an improved understanding of the role of hemodynamics in neural processing, as it directly bears on interpretation of and potential treatment for stroke, dementia and epilepsy.

Inactivation of dorsolateral striatum enhances sensitivity to changes in the action-outcome contingency in instrumental conditioning.

HH Yin — 2006-11-27T18:40:37-00:00

Behav Brain Res, Vol. 166, No. 2. (30 January 2006), pp. 189-196.

Actions become compulsive when they are no longer controlled by their consequences. Compulsivity can be assessed using the omission procedure in which animals are required to withhold a previously reinforced action to earn reward. The current study tested the hypothesis that inactivation of the dorsolateral striatum (DLS), a structure implicated in habitual behavior, can enhance sensitivity to changes in the action-outcome contingency during omission training, thus leading to a reduction in compulsive responding. Over 10 days rats were trained to press a freely available lever for sucrose reward delivered on interval schedules of reinforcement. After learning to press the lever at a stable and high rate, rats in the omission group received a session in which the rewards were now delayed by pressing the lever; i.e. withholding lever pressing resulted in increased access to reward. A control group was yoked to the omission group and received the same number and pattern of reward delivery but without the omission contingency. Half the rats in each group received infusions of vehicle into the DLS prior to this training whereas the remainder received an infusion of the GABA-A receptor agonist muscimol. On the next day, the effect of these treatments was assessed on a probe test in which the tendency of the various groups to press the lever was assessed in extinction and without drug infusion. Rats that received vehicle infusions prior to the omission session showed complete insensitivity to the newly imposed omission contingency. In contrast, rats given the infusion of muscimol selectively reduced lever pressing compared to yoked controls. Thus, extended training with interval schedules resulted in compulsive lever pressing that prevented the learning of the omission contingency, whereas inactivation of the DLS appeared to enhance the rats' sensitivity to this change in the action-outcome contingency.

Reward prediction in primate basal ganglia and frontal cortex

Wolfram Schultz — 2007-07-23T18:32:24-00:00

Neuropharmacology, Vol. 37, No. 4-5. (5 April 1998), pp. 421-429.

Reward information is processed in a limited number of brain structures, including fronto-basal ganglia systems. Dopamine neurons respond phasically to primary rewards and reward-predicting stimuli depending on reward unpredictability but without discriminating between rewards. These responses reflect `errors' in the prediction of rewards in correspondence to learning theories and thus may constitute teaching signals for appetitive learning. Neurons in the striatum (caudate, putamen, ventral striatum) code reward predictions in a different manner. They are activated during several seconds when animals expect predicted rewards. During learning, these activations occur initially in rewarded and unrewarded trials and become subsequently restricted to rewarded trials. This occurs in parallel with the adaptation of reward expectations by the animals, as inferred from their behavioral reactions. Neurons in orbitofrontal cortex respond differentially to stimuli predicting different liquid rewards, without coding spatial or visual features. Thus, different structures process reward information processed in different ways. Whereas dopamine neurons emit a reward teaching signal without indicating the specific reward, striatal neurons adapt expectation activity to new reward situations, and orbitofrontal neurons process the specific nature of rewards. These reward signals need to cooperate in order for reward information to be used for learning and maintaining approach behavior.

Goal-directed instrumental action: contingency and incentive learning and their cortical substrates

Bernard Balleine — 2007-07-23T18:29:47-00:00

Neuropharmacology, Vol. 37, No. 4-5. (5 April 1998), pp. 407-419.

Instrumental behaviour is controlled by two systems: a stimulus-response habit mechanism and a goal-directed process that involves two forms of learning. The first is learning about the instrumental contingency between the response and reward, whereas the second consists of the acquisition of incentive value by the reward. Evidence for contingency learning comes from studies of reward devaluation and from demonstrations that instrumental performance is sensitive not only the probability of contiguous reward but also to the probability of unpaired rewards. The process of incentive learning is evident in the acquisition of control over performance by primary motivational states. Preliminary lesion studies of the rat suggest that the prelimibic area of prefrontal cortex plays a role in the contingency learning, whereas the incentive learning for food rewards involves the insular cortex.

Neural signature of fictive learning signals in a sequential investment task

Terry Lohrenz — 2007-07-23T13:26:29-00:00

PNAS, Vol. 104, No. 22. (29 May 2007), pp. 9493-9498.

Reinforcement learning models now provide principled guides for a wide range of reward learning experiments in animals and humans. One key learning (error) signal in these models is experiential and reports ongoing temporal differences between expected and experienced reward. However, these same abstract learning models also accommodate the existence of another class of learning signal that takes the form of a fictive error encoding ongoing differences between experienced returns and returns that "could-have-been-experienced" if decisions had been different. These observations suggest the hypothesis that, for all real-world learning tasks, one should expect the presence of both experiential and fictive learning signals. Motivated by this possibility, we used a sequential investment game and fMRI to probe ongoing brain responses to both experiential and fictive learning signals generated throughout the game. Using a large cohort of subjects (n = 54), we report that fictive learning signals strongly predict changes in subjects' investment behavior and correlate with fMRI signals measured in dopaminoceptive structures known to be involved in valuation and choice. 10.1073/pnas.0608842104

Tryptophan depletion reduces right inferior prefrontal activation during response inhibition in fast, event-related fMRI

Katya Rubia — 2007-07-16T21:13:02-00:00

Psychopharmacology, Vol. 179, No. 4. (1 June 2005), pp. 791-803.

Abstract

The effect of tryptophan depletion on brain activation measured by functional magnetic resonance imaging during the Stroop test in healthy subjects.

J Horácek — 2007-07-16T21:11:47-00:00

Physiol Res, Vol. 54, No. 2. (2005), pp. 235-244.

We investigated the role of serotonin in cognitive activation of the frontal cortex. The serotonergic system was affected by the administration of an amino acids mixture without tryptophan (tryptophan depletion). In a placebo-controlled double-blind cross-over study with 20 healthy volunteers, we tested the hypothesis that a tryptophan (serotonin) decrease affects the activation of prefrontal cortex by the Stroop test. Cognitive brain activation was evaluated by functional magnetic resonance imaging (fMRI). Tryptophan depletion decreased the plasma tryptophan level up to 90 % for five hours after the tryptophan-free drink had been consumed when compared with the same mixture with tryptophan (p?0.0001). Tryptophan depletion did not affect the Stroop test performance. We compared fMRI activation in both conditions (tryptophan depletion and placebo) with plasma tryptophan levels as the covariates. The tryptophan depletion increased the activation (fMRI signal) in the bilateral mediofrontal cortex, anterior cingulate and left dorsolateral prefrontal cortex. The present findings allow the postulate that serotonergic medial forebrain and cingulum bundle pathways play a role in the activity of cortical structures involved in Stroop test processing.

Tryptophan depletion and its implications for psychiatry

Caroline Bell — 2007-07-16T21:09:02-00:00

Br J Psychiatry, Vol. 178, No. 5. (1 May 2001), pp. 399-405.

Background Over the past 10 years the technique of tryptophan depletion has been used increasingly as a tool for studying brain serotonergic systems. Aims To review the technique of tryptophan depletion and its current status as a tool for investigating psychiatric disorders. Method Systematic review of preclinical and clinical studies. Results Tryptophan depletion produces a marked reduction in plasma tryptophan and consequently brain serotonin (5-HT) synthesis and release. In healthy volunteers the effects of tryptophan depletion are influenced by the characteristics of the subjects and include some mood lowering, some memory impairment and an increase in aggression. In patients with depression tryptophan depletion tends to result in no worsening of depression in untreated subjects but a relapse in those who have responded to antidepressants (particularly serotonergic agents). In panic disorder the results are similar. Conclusions The findings that tryptophan depletion produces a relapse of symptoms in patients with depression and panic disorder who have responded to treatment with antidepressants suggests that enhanced 5-HT function is important in maintaining response in these conditions. 10.1192/bjp.178.5.399

Tryptophan depletion in SSRI-recovered depressed outpatients

Maya Spillmann — 2007-07-16T21:07:13-00:00

Psychopharmacology, Vol. 155, No. 2. (2 May 2001), pp. 123-127.

Rationale: Recently, a number of studies have challenged the finding that acute tryptophan depletion (TD) increases depressive symptoms in medicated, formerly depressed patients. The present study examined the effects of acute nutritional TD on remitted depressed patients currently treated with selective serotonin reuptake inhibitors. In an attempt to clarify conflicting earlier findings, the effects of a number of clinical variables on outcome were also investigated. Methods: Ten patients underwent TD in a double-blind, controlled, balanced crossover fashion. The control session followed the procedure of Krahn et al. (1996 Neuropsychopharmacology 15:325-328). Sessions were 5-8 days apart. Results: TD was significantly related to increased scores on clinician-rated depression and anxiety scales, and on self-rated depression, anxiety, and somatic symptoms. The control challenge had no effect, despite the fact that the reductions in plasma tryptophan during the control session were unexpectedly high. Some evidence was found for a threshold in the relationship between reduction of plasma tryptophan and mood response. Conclusions: The mood effect of TD in medicated, formerly depressed patients was confirmed. A threshold may exist for mood effects following TD, implying that recent negative findings may have been caused by insufficient depletion. No other predicting or mediating factors were identified, although the variable "history of response pattern to medication" deserves further study.

Neural Systems Responding to Degrees of Uncertainty in Human Decision-Making

Ming Hsu — 2006-01-16T11:14:30-00:00

Science, Vol. 310, No. 5754. (9 December 2005), pp. 1680-1683.

Much is known about how people make decisions under varying levels of probability (risk). Less is known about the neural basis of decision-making when probabilities are uncertain because of missing information (ambiguity). In decision theory, ambiguity about probabilities should not affect choices. Using functional brain imaging, we show that the level of ambiguity in choices correlates positively with activation in the amygdala and orbitofrontal cortex, and negatively with a striatal system. Moreover, striatal activity correlates positively with expected reward. Neurological subjects with orbitofrontal lesions were insensitive to the level of ambiguity and risk in behavioral choices. These data suggest a general neural circuit responding to degrees of uncertainty, contrary to decision theory.

Observational learning: effects of bandwidth knowledge of results.

A Badets — 2007-07-13T19:07:03-00:00

J Mot Behav, Vol. 37, No. 3. (May 2005), pp. 211-216.

The authors investigated whether bandwidth knowledge of results (KR) during observation of a model's performance enhances motor skill learning. Following a pretest, 2 groups of participants (N = 28) observed a model practicing a timing task. The bandwidth group received KR about the model's performance only when his performance fell outside the criteria for a correct response. The yoked group received KR on the same trials as the bandwidth group did but were not told that the KR was only about incorrect performances. In that way, the authors avoided a confound between bandwidth and relative frequency effects on performance and learning. Following the observation phase, both groups of participants performed 10-min and 24-hr retention tests. Bandwidth KR enabled that group to reduce its performance variability and, to a lesser extent, to enhance its performance accuracy. The authors discuss the results with respect to the powerful effect of qualitative KR through observation.

The Reward Event and Motivation

Carolyn Morillo — 2007-07-16T12:51:10-00:00

The Journal of Philosophy, Vol. 87, No. 4. (1990), pp. 169-186.

A Dual-Self Model of Impulse Control

Fudenberg — 2007-01-11T05:44:22-00:00

The American Economic Review, Vol. 96, No. 5. (December 2006), pp. 1449-1476.

Addiction and Cue-Triggered Decision Processes

Douglas Bernheim — 2005-02-11T05:36:21-00:00

The American Economic Review, Vol. 94, No. 5. (December 2004), pp. 1558-1590.

The Neural Basis of Love as a Subliminal Prime: An Event-related Functional Magnetic Resonance Imaging Study

S Ortigue — 2007-07-02T12:50:44-00:00

J. Cogn. Neurosci., Vol. 19, No. 7. (1 July 2007), pp. 1218-1230.

Throughout the ages, love has been defined as a motivated and goal-directed mechanism with explicit and implicit mechanisms. Recent evidence demonstrated that the explicit representation of love recruits subcorticocortical pathways mediating reward, emotion, and motivation systems. However, the neural basis of the implicit (unconscious) representation of love remains unknown. To assess this question, we combined event-related functional magnetic resonance imaging (fMRI) with a behavioral subliminal priming paradigm embedded in a lexical decision task. In this task, the name of either a beloved partner, a neutral friend, or a passionate hobby was subliminally presented before a target stimulus (word, nonword, or blank), and participants were required to decide if the target was a word or not. Behavioral results showed that subliminal presentation of either a beloved's name (love prime) or a passion descriptor (passion prime) enhanced reaction times in a similar fashion. Subliminal presentation of a friend's name (friend prime) did not show any beneficial effects. Functional results showed that subliminal priming with a beloved's name (as opposed to either a friend's name or a passion descriptor) specifically recruited brain areas involved in abstract representations of others and the self, in addition to motivation circuits shared with other sources of passion. More precisely, love primes recruited the fusiform and angular gyri. Our findings suggest that love, as a subliminal prime, involves a specific neural network that surpasses a dopaminergic-motivation system.

Neural mechanisms of aggression

Randy Nelson — 2007-06-20T17:30:22-00:00

Nat Rev Neurosci, Vol. 8, No. 7. (July 2007), pp. 536-546.

Imitation, mirror neurons and autism.

JH Williams — 2006-05-17T17:20:58-00:00

Neurosci Biobehav Rev, Vol. 25, No. 4. (June 2001), pp. 287-295.

Various deficits in the cognitive functioning of people with autism have been documented in recent years but these provide only partial explanations for the condition. We focus instead on an imitative disturbance involving difficulties both in copying actions and in inhibiting more stereotyped mimicking, such as echolalia. A candidate for the neural basis of this disturbance may be found in a recently discovered class of neurons in frontal cortex, 'mirror neurons' (MNs). These neurons show activity in relation both to specific actions performed by self and matching actions performed by others, providing a potential bridge between minds. MN systems exist in primates without imitative and 'theory of mind' abilities and we suggest that in order for them to have become utilized to perform social cognitive functions, sophisticated cortical neuronal systems have evolved in which MNs function as key elements. Early developmental failures of MN systems are likely to result in a consequent cascade of developmental impairments characterised by the clinical syndrome of autism.

Intuitive psychology and physics among children with autism and typically developing children.

L Binnie — 2006-05-12T18:39:06-00:00

Autism, Vol. 7, No. 2. (June 2003), pp. 173-193.

Many studies have documented poor understanding of intuitive psychology among children with autism; however, few have investigated claims of superior understanding of intuitive physics said to be evident in this group. This study aimed to investigate the reported differential preference of intuitive psychology and intuitive physics among children with autism by employing three tasks each with a psychological and a physical condition. In order to gain a detailed developmental picture the study compared children with autism, an age matched comparison group, and typically developing preschoolers, 7-year-olds and 10-year-olds. Results demonstrated that children with autism preferred to employ physical causality when reasoning about novel physical and psychological events. Furthermore, their performance on a multiple-choice task confirmed their impairment in intuitive psychology whilst highlighting a superior ability to reason about physical phenomena in relation to all other comparison groups. The theoretical implications of this potential cognitive strength are discussed.

Measuring empathy: reliability and validity of the Empathy Quotient.

EJ Lawrence — 2007-06-19T18:08:43-00:00

Psychol Med, Vol. 34, No. 5. (July 2004), pp. 911-919.

BACKGROUND: Empathy plays a key role in social understanding, but its empirical measurement has proved difficult. The Empathy Quotient (EQ) is a self-report scale designed to do just that. This series of four studies examined the reliability and validity of the EQ and determined its factor structure. METHOD: In Study 1, 53 people completed the EQ, Social Desirability Scale (SDS) and a non-verbal mental state inference test, the Eyes Task. In Study 2, a principal components analysis (PCA) was conducted on data from 110 healthy individuals and 62 people reporting depersonalisation (DPD). Approximately 1 year later, Study 3, involved the re-administration of the EQ (n = 24) along with the Interpersonal Reactivity Index (IRI; n = 28). In the last study, the EQ scores of those with DPD, a condition that includes a subjective lack of empathy, were examined in depth. RESULTS: An association was found between the Eyes task and EQ, and only three EQ items correlated with the SDS. PCA revealed three factors: (1) 'cognitive empathy'; (2) 'emotional reactivity', and (3) 'social skills'. Test-retest reliability was good and moderate associations were found between the EQ and IRI subscales, suggesting concurrent validity. People with DPD did not show a global empathy deficit, but reported less social competence. CONCLUSIONS: The EQ is a valid, reliable scale and the different subscales may have clinical applications.

Neuroactive hormones and interpersonal trust: international evidence.

PJ Zak — 2007-06-19T17:57:53-00:00

Econ Hum Biol, Vol. 4, No. 3. (December 2006), pp. 412-429.

Social attachment is vital for human health and welfare. Recent experimental evidence in humans has identified the role of neuroactive hormones, especially the peptide oxytocin, in mediating trusting behaviors. Herein, we test if the endocrinological basis for trust between humans scales up to the country level. Trust pervades nearly every aspect of our daily lives, yet survey data on trust show substantial variation across countries. Using 31 measures of biological, social, and environmental factors associated with hormone levels for a sample of 41 countries, we find that two classes of factors are related to trust: consumption of plant-based estrogens (phytoestrogens), and the presence of environmental conditions that include measures of estrogen-like molecules. Our findings provide preliminary evidence that interpersonal trust at the country level may be related to the intake of neuroactive hormones.