CiteULike: Group: Glimcher_Lab - with tag human

Differences in Cortical Serotonergic Innervation among Humans, Chimpanzees, and Macaque Monkeys: A Comparative Study

Mary Raghanti — 2007-11-16T13:58:07-00:00

Cereb. Cortex (22 June 2007), bhm089.

In this study, we assess the possibility that the evolution of human intellectual capacities was supported by changes in the supply of serotonin to the frontal cortex. To this end, quantitative comparative analyses were performed among humans, chimpanzees, and macaques. Immunohistochemical methods were used to visualize serotonin transporter-immunoreactive (SERT-ir) axons within the cerebral cortex. Areas 9 and 32 were chosen for evaluation due to their roles in working memory and theory of mind, respectively. Primary motor cortex was also evaluated because it is not associated with higher cognitive functions. The findings revealed that humans do not display a quantitative increase in serotonin innervation. However, the results indicated region- and layer-specific differences among species in serotonergic innervation pattern. Compared with macaques, humans and chimpanzees together displayed a greater density of SERT-ir axons relative to neuron density in layers V/VI. This change was detected in cortical areas 9 and 32, but not in primary motor cortex. Further, morphological specializations, coils of axons, were observed in humans and chimpanzees that were absent in macaques. These features may represent a greater capacity for cortical plasticity exclusive to hominoids. Taken together, these results indicate a significant reorganization of cortical serotonergic transmission in humans and chimpanzees. 10.1093/cercor/bhm089

Dissociating uncertainty responses and reinforcement signals in the comparative study of uncertainty monitoring.

JD Smith — 2007-11-25T17:18:54-00:00

J Exp Psychol Gen, Vol. 135, No. 2. (May 2006), pp. 282-297.

Although researchers are exploring animals' capacity for monitoring their states of uncertainty, the use of some paradigms allows the criticism that animals map avoidance responses to error-causing stimuli not because of uncertainty monitored but because of feedback signals and stimulus aversion. The authors addressed this criticism with an uncertainty-monitoring task in which participants completed blocks of trials with feedback deferred so that they could not associate reinforcement signals to particular stimuli or stimulus-response pairs. Humans and 1 of 2 monkeys were able to make cognitive, decisional uncertainty responses that were independent of feedback or reinforcement history within a task. This finding unifies the comparative literature on uncertainty monitoring. The dissociation of performance from reinforcement has theoretical implications, and the deferred-feedback technique has many applications.

The uniquely human capacity to throw evolved from a non-throwing primate: an evolutionary dissociation between action and perception.

JN Wood — 2008-01-02T15:56:38-00:00

Biol Lett, Vol. 3, No. 4. (22 August 2007), pp. 360-364.

Humans are uniquely endowed with the ability to engage in accurate, high-momentum throwing. Underlying this ability is a unique morphological adaptation that enables the characteristic rotation of the arm and pelvis. What is unknown is whether the psychological mechanisms that accompany the act of throwing are also uniquely human. Here we explore this problem by asking whether free-ranging rhesus monkeys (Macaca mulatta), which lack both the morphological and neural structures to throw, nonetheless recognize the functional properties of throwing. Rhesus not only understand that human throwing represents a threat, but that some aspects of a throwing event are more relevant than others; specifically, rhesus are sensitive to the kinematics, direction and speed of the rotating arm, the direction of the thrower's eye gaze and the object thrown. These results suggest that the capacity to throw did not coevolve with psychological mechanisms that accompany throwing; rather, this capacity may have built upon pre-existing perceptual processes. These results are consistent with a growing body of work showing that non-human animals often exhibit perceptual competencies that do not show up in their motor responses, suggesting evolutionary dissociations between the systems of perception that provide understanding of the world and those that mediate action on the world.

The evolutionary origins of human patience: temporal preferences in chimpanzees, bonobos, and human adults.

AG Rosati — 2008-01-02T15:54:02-00:00

Curr Biol, Vol. 17, No. 19. (9 October 2007), pp. 1663-1668.

To make adaptive choices, individuals must sometimes exhibit patience, forgoing immediate benefits to acquire more valuable future rewards [1-3]. Although humans account for future consequences when making temporal decisions [4], many animal species wait only a few seconds for delayed benefits [5-10]. Current research thus suggests a phylogenetic gap between patient humans and impulsive, present-oriented animals [9, 11], a distinction with implications for our understanding of economic decision making [12] and the origins of human cooperation [13]. On the basis of a series of experimental results, we reject this conclusion. First, bonobos (Pan paniscus) and chimpanzees (Pan troglodytes) exhibit a degree of patience not seen in other animals tested thus far. Second, humans are less willing to wait for food rewards than are chimpanzees. Third, humans are more willing to wait for monetary rewards than for food, and show the highest degree of patience only in response to decisions about money involving low opportunity costs. These findings suggest that core components of the capacity for future-oriented decisions evolved before the human lineage diverged from apes. Moreover, the different levels of patience that humans exhibit might be driven by fundamental differences in the mechanisms representing biological versus abstract rewards.

Area under the curve as a measure of discounting.

J Myerson — 2007-09-12T15:39:45-00:00

J Exp Anal Behav, Vol. 76, No. 2. (September 2001), pp. 235-243.

We describe a novel approach to the measurement of discounting based on calculating the area under the empirical discounting function. This approach avoids some of the problems associated with measures based on estimates of the parameters of theoretical discounting functions. The area measure may be easily calculated for both individual and group data collected using any of a variety of current delay and probability discounting procedures. The present approach is not intended as a substitute for theoretical discounting models. It is useful, however, to have a simple, univariate measure of discounting that is not tied to any specific theoretical framework.

Three-month stability of delay and probability discounting measures.

Y Ohmura — 2007-09-07T21:22:15-00:00

Exp Clin Psychopharmacol, Vol. 14, No. 3. (August 2006), pp. 318-328.

Psychopharmacologists are interested in delay and probability discounting because the tendency to discount the value of future and uncertain rewards has been linked with drug dependency. However, relatively little is known about the long-term stability of discounting measures typically studied in clinical psychopharmacology. To evaluate the stability of discounting over a 3-month period, the authors compared points of subjective equality (indifference points) with those collected from the same subjects 3 months earlier. Seven delay periods, ranging from 1 week to 25 years, and 7 probability values, ranging from .95 to .05, were assessed in an undergraduate sample (n=22, delay discounting; n=18, probability discounting). The authors examined both differential stability (stability of individual differences) and absolute stability (stability of the group mean) of delay and probability discounting measures as well as their respective indifference points. The results demonstrate that standard delay and probability discounting parameters (e.g., hyperbolic k and area under the curve) had both differential stability and absolute stability across 3 months. Moreover, most indifference points in the delay and probability discounting tasks demonstrated both differential and absolute stability. All together, these results suggest that delay and probability parameters are stable enough to predict future behavior, such as substance abuse. Additional findings indicated that a hyperbolic function fitted the data better than an exponential function and that delay and probability discounting parameters were not significantly correlated.

Why Don't We Move Faster? Parkinson's Disease, Movement Vigor, and Implicit Motivation

Pietro Mazzoni — 2007-07-05T13:31:55-00:00

J. Neurosci., Vol. 27, No. 27. (4 July 2007), pp. 7105-7116.

People generally select a similar speed for a given motor task, such as reaching for a cup. One well established determinant of movement time is the speed-accuracy trade-off: movement time increases with the accuracy requirement. A second possible determinant is the energetic cost of making a movement. Parkinson's disease (PD), a condition characterized by generalized movement slowing (bradykinesia), provides the opportunity to directly explore this second possibility. We compared reaching movements of patients with PD with those of control subjects in a speed-accuracy trade-off task comprising conditions of increasing difficulty. Subjects completed as many trials as necessary to make 20 movements within a required speed range (trials to criterion, Nc). Difficulty was reflected in endpoint accuracy and Nc. Patients were as accurate as control subjects in all conditions (i.e., PD did not affect the speed-accuracy trade-off). However, Nc was consistently higher in patients, indicating reluctance to move fast although accuracy was not compromised. Specifically, the dependence of Nc on movement energy cost (slope SN) was steeper in patients than in control subjects. This difference in SN suggests that bradykinesia represents an implicit decision not to move fast because of a shift in the cost/benefit ratio of the energy expenditure needed to move at normal speed. SN was less steep, but statistically significant, in control subjects, which demonstrates a role for energetic cost in the normal control of movement speed. We propose that, analogous to the established role of dopamine in explicit reward-seeking behavior, the dopaminergic projection to the striatum provides a signal for implicit "motor motivation." 10.1523/JNEUROSCI.0264-07.2007

Maximizing versus satisficing: happiness is a matter of choice.

B Schwartz — 2007-07-03T16:29:23-00:00

J Pers Soc Psychol, Vol. 83, No. 5. (November 2002), pp. 1178-1197.

Can people feel worse off as the options they face increase? The present studies suggest that some people--maximizers--can. Study 1 reported a Maximization Scale, which measures individual differences in desire to maximize. Seven samples revealed negative correlations between maximization and happiness, optimism, self-esteem, and life satisfaction, and positive correlations between maximization and depression, perfectionism, and regret. Study 2 found maximizers less satisfied than nonmaximizers (satisficers) with consumer decisions, and more likely to engage in social comparison. Study 3 found maximizers more adversely affected by upward social comparison. Study 4 found maximizers more sensitive to regret and less satisfied in an ultimatum bargaining game. The interaction between maximizing and choice is discussed in terms of regret, adaptation, and self-blame.

Self-determination. The tyranny of freedom.

B Schwartz — 2007-07-03T16:28:40-00:00

Am Psychol, Vol. 55, No. 1. (January 2000), pp. 79-88.

Americans now live in a time and a place in which freedom and autonomy are valued above all else and in which expanded opportunities for self-determination are regarded as a sign of the psychological well-being of individuals and the moral well-being of the culture. This article argues that freedom, autonomy, and self-determination can become excessive, and that when that happens, freedom can be experienced as a kind of tyranny. The article further argues that unduly influenced by the ideology of economics and rational-choice theory, modern American society has created an excess of freedom, with resulting increases in people's dissatisfaction with their lives and in clinical depression. One significant task for a future psychology of optimal functioning is to deemphasize individual freedom and to determine which cultural constraints are necessary for people to live meaningful and satisfying lives.

The tyranny of choice.

B Schwartz — 2007-07-03T16:25:54-00:00

Sci Am, Vol. 290, No. 4. (April 2004), pp. 70-75.

When choice is demotivating: can one desire too much of a good thing?

SS Iyengar — 2007-07-03T16:23:42-00:00

J Pers Soc Psychol, Vol. 79, No. 6. (December 2000), pp. 995-1006.

Current psychological theory and research affirm the positive affective and motivational consequences of having personal choice. These findings have led to the popular notion that the more choice, the better-that the human ability to manage, and the human desire for, choice is unlimited. Findings from 3 experimental studies starkly challenge this implicit assumption that having more choices is necessarily more intrinsically motivating than having fewer. These experiments, which were conducted in both field and laboratory settings, show that people are more likely to purchase gourmet jams or chocolates or to undertake optional class essay assignments when offered a limited array of 6 choices rather than a more extensive array of 24 or 30 choices. Moreover, participants actually reported greater subsequent satisfaction with their selections and wrote better essays when their original set of options had been limited. Implications for future research are discussed.

The molecular genetic architecture of human personality: beyond self-report questionnaires

RP Ebstein — 2006-03-14T11:12:19-00:00

Molecular Psychiatry, Vol. aop, No. current.

Activation of Prefrontal Cortex by Transcranial Direct Current Stimulation Reduces Appetite for Risk during Ambiguous Decision Making

Shirley Fecteau — 2007-06-07T14:08:41-00:00

J. Neurosci., Vol. 27, No. 23. (6 June 2007), pp. 6212-6218.

As adult humans, we are continuously faced with decisions in which proper weighing of the risk involved is critical. Excessively risky or overly cautious decision making can both have disastrous real-world consequences. Weighing of risks and benefits toward decision making involves a complex neural network that includes the dorsolateral prefrontal cortex (DLPFC), but its role remains unclear. Repetitive transcranial magnetic stimulation studies have shown that disruption of the DLPFC increases risk-taking behavior. Transcranial direct current stimulation (tDCS) allows upregulation of activity in the DLPFC, and we predicted that it might promote more cautious decision making. Healthy participants received one of the following treatments while they performed the Balloon Analog Risk Task: (1) right anodal/left cathodal DLPFC tDCS, (2) left anodal/ right cathodal DLPFC tDCS, or (3) sham tDCS. This experiment revealed that participants receiving either one of the bilateral DLPFC tDCS strategies adopted a risk-averse response style. In a control experiment, we tested whether unilateral DLPFC stimulation (anodal tDCS over the right or left DLPFC with the cathodal electrode over the contralateral supraorbital area) was sufficient to decrease risk-taking behaviors. This experiment showed no difference in decision-making behaviors between the groups of unilateral DLPFC stimulation and sham stimulation. These findings extend the notion that DLPFC activity is critical for adaptive decision making, possibly by suppressing riskier responses. Anodal tDCS over DLPFC by itself did not significantly change risk-taking behaviors; however, when the contralateral DLPFC was modulated with cathodal tCDS, an important decrease in risk taking was observed. Also, the induced cautious decision-making behavior was observed only when activity of both DLPFCs was modulated. The ability to modify risk-taking behavior may be translated into therapeutic interventions for disorders such as drug abuse, overeating, or pathological gambling. 10.1523/JNEUROSCI.0314-07.2007

Dopaminergic modulation of impaired cognitive activation in the anterior cingulate cortex in schizophrenia

RJ Dolan — 2007-05-24T17:51:22-00:00

Nature, Vol. 378, No. 6553. (November 1995), pp. 180-182.

Dissociating prefrontal and hippocampal function in episodic memory encoding

RJ Dolan — 2007-05-24T17:47:46-00:00

Nature, Vol. 388, No. 6642. (1997), pp. 582-585.

Anatomical Segregation of Component Processes in an Inductive Inference Task

Vinod Goel — 2007-05-24T17:45:06-00:00

J. Cogn. Neurosci., Vol. 12, No. 1. (1 January 2000), pp. 110-119.

Inductive inference underlies much of human cognition. The essential component of induction is hypothesis selection based on some criterion of relevance. The purpose of this study was to determine the neural substrate of inductive inference, particularly hypothesis selection, using fMRI. Ten volunteers were shown stimuli consisting of novel animals under two task conditions, and asked to judge whether all the animals in the set were the same type of animal. In one condition, subjects were given a rule that specified the criteria for "same type of animal". In the other condition, subjects had to infer the rule without instruction. The two conditions were further factored into easy and difficult components. Rule inference was specifically associated with bilateral hippocampal activation while the task by difficulty interaction was associated with activation in right lateral orbital prefrontal cortex. We interpret the former in terms of semantic encoding of novel stimuli and the latter in terms of hypothesis selection. Thus, we show an anatomical dissociation between task implementation and task difficulty that may correspond to a critical psychological distinction in the processes necessary for inductive inference.

Time Discounting for Primary Rewards

Samuel Mcclure — 2007-05-23T18:23:55-00:00

J. Neurosci., Vol. 27, No. 21. (23 May 2007), pp. 5796-5804.

Previous research, involving monetary rewards, found that limbic reward-related areas show greater activity when an intertemporal choice includes an immediate reward than when the options include only delayed rewards. In contrast, the lateral prefrontal and parietal cortex (areas commonly associated with deliberative cognitive processes, including future planning) respond to intertemporal choices in general but do not exhibit sensitivity to immediacy (McClure et al., 2004). The current experiments extend these findings to primary rewards (fruit juice or water) and time delays of minutes instead of weeks. Thirsty subjects choose between small volumes of drinks delivered at precise times during the experiment (e.g., 2 ml now vs 3 ml in 5 min). Consistent with previous findings, limbic activation was greater for choices between an immediate reward and a delayed reward than for choices between two delayed rewards, whereas the lateral prefrontal cortex and posterior parietal cortex responded similarly whether choices were between an immediate and a delayed reward or between two delayed rewards. Moreover, relative activation of the two sets of brain regions predicts actual choice behavior. A second experiment finds that when the delivery of all rewards is offset by 10 min (so that the earliest available juice reward in any choice is 10 min), no differential activity is observed in limbic reward-related areas for choices involving the earliest versus only more delayed rewards. We discuss implications of this finding for differences between primary and secondary rewards. 10.1523/JNEUROSCI.4246-06.2007

Discounting of Monetary and Directly Consumable Rewards

Estle — 2007-03-13T01:31:27-00:00

Psychological Science, Vol. 18, No. 1. (January 2007), pp. 58-63.

The roles of the caudate nucleus in human classification learning.

CA Seger — 2007-02-27T03:35:05-00:00

J Neurosci, Vol. 25, No. 11. (16 March 2005), pp. 2941-2951.

The caudate nucleus is commonly active when learning relationships between stimuli and responses or categories. Previous research has not differentiated between the contributions to learning in the caudate and its contributions to executive functions such as feedback processing. We used event-related functional magnetic resonance imaging while participants learned to categorize visual stimuli as predicting "rain" or "sun." In each trial, participants viewed a stimulus, indicated their prediction via a button press, and then received feedback. Conditions were defined on the bases of stimulus-outcome contingency (deterministic, probabilistic, and random) and feedback (negative and positive). A region of interest analysis was used to examine activity in the head of the caudate, body/tail of the caudate, and putamen. Activity associated with successful learning was localized in the body and tail of the caudate and putamen; this activity increased as the stimulus-outcome contingencies were learned. In contrast, activity in the head of the caudate and ventral striatum was associated most strongly with processing feedback and decreased across trials. The left superior frontal gyrus was more active for deterministic than probabilistic stimuli; conversely, extrastriate visual areas were more active for probabilistic than deterministic stimuli. Overall, hippocampal activity was associated with receiving positive feedback but not with correct classification. Successful learning correlated positively with activity in the body and tail of the caudate nucleus and negatively with activity in the hippocampus.

Deep brain stimulation for neurologic and neuropsychiatric disorders.

T Wichmann — 2007-01-04T22:37:41-00:00

Neuron, Vol. 52, No. 1. (5 October 2006), pp. 197-204.

In the 1960s, ablative stereotactic surgery was employed for a variety of movement disorders and psychiatric conditions. Although largely abandoned in the 1970s because of highly effective drugs, such as levodopa for Parkinson's disease (PD), and a reaction against psychosurgery, the field has undergone a virtual renaissance, guided by a better understanding of brain circuitry and the circuit abnormalities underlying movement disorders such as PD and neuropsychiatric conditions, such as obsessive compulsive disorder. High-frequency electrical deep brain stimulation (DBS) of specific targets, introduced in the early 1990s for tremor, has gained widespread acceptance because of its less invasive, reversible, and adjustable features and is now utilized for an increasing number of brain disorders. This review summarizes the rationale behind DBS and the use of this technique for a variety of movement disorders and neuropsychiatric diseases.

Preference for immediate over delayed rewards is associated with magnitude of ventral striatal activity.

AR Hariri — 2007-01-02T20:20:02-00:00

J Neurosci, Vol. 26, No. 51. (20 December 2006), pp. 13213-13217.

Discounting future outcomes as a function of their deferred availability underlies much of human decision making. Discounting, or preference for immediate over delayed rewards of larger value, is often associated with impulsivity and is a risk factor for addictive disorders such as pathological gambling, cigarette smoking, and drug and alcohol abuse. The ventral striatum (VS) is involved in mediating behavioral responses and physiological states associated with reward, and dysregulation of the VS contributes to addiction, perhaps by affecting impulsive decision-making. Behavioral tests of delay discounting (DD), which index preference for smaller immediate over larger delayed rewards, covary with impulsive tendencies in humans. In the current study, we examined the relationship between individual differences in DD, measured in a behavioral assessment, and VS activity measured with blood oxygenation level-dependent functional magnetic resonance imaging, in 45 adult volunteers. VS activity was determined using a task involving positive and negative feedback with monetary reward. Analyses revealed that individual differences in DD correlate positively with magnitude of VS activation in response to both positive and negative feedback, compared with a no-feedback control condition. Variability in DD was also associated with differential VS activation in response to positive, compared with negative, feedback. Collectively, our results suggest that increased preference for smaller immediate over larger delayed rewards reflects both a relatively indiscriminate and hyper-reactive VS circuitry. They also highlight a specific neurocognitive mechanism that may contribute to increased risk for addiction.

Humans Can Adopt Optimal Discounting Strategy under Real-Time Constraints.

N Schweighofer — 2006-11-25T17:53:55-00:00

PLoS Comput Biol, Vol. 2, No. 11. (10 November 2006)

Critical to our many daily choices between larger delayed rewards, and smaller more immediate rewards, are the shape and the steepness of the function that discounts rewards with time. Although research in artificial intelligence favors exponential discounting in uncertain environments, studies with humans and animals have consistently shown hyperbolic discounting. We investigated how humans perform in a reward decision task with temporal constraints, in which each choice affects the time remaining for later trials, and in which the delays vary at each trial. We demonstrated that most of our subjects adopted exponential discounting in this experiment. Further, we confirmed analytically that exponential discounting, with a decay rate comparable to that used by our subjects, maximized the total reward gain in our task. Our results suggest that the particular shape and steepness of temporal discounting is determined by the task that the subject is facing, and question the notion of hyperbolic reward discounting as a universal principle.

Time-estimation error following Weber-Fechner law may explain subadditive time-discounting.

T Takahashi — 2006-11-15T23:34:56-00:00

Med Hypotheses, Vol. 67, No. 6. (2006), pp. 1372-1374.

Impulsivity in drug addicts have been associated with impatience in intertemporal choice, i.e., high degrees to which delayed rewards are discounted, indicating the importance of reducing the degree of discounting in drug addicts. Intertemporal choice (delay discounting) has been attracting attention in neuropsychopharmacology and behavioral neuroeconomics. Recently, behavioral economists have reported that impatience/impulsivity in intertemporal choice is increased if a delay period is presented as a sum of divided time-blocks, which is referred to as subadditive discounting (i.e., "total patience" over the delay period is larger than the "sum of patience" over divided delay periods). This finding implies that abstinent drug addicts may more readily relapse into addiction if an abstinence period is presented as a series of shorter abstinent periods, rather than a single block of a long abstinence period. Therefore, understanding of neuropsychological processing underlying subadditive discounting is important for establishing medical treatments of drug addiction, although to date, no study has addressed this question. In this study, we propose that time-estimation following Weber-Fechner law, formerly introduced for explaining hyperbolic discounting, may also explain subadditive discounting. Our present hypothesis also predicts that possibility of relapse into drug dependence can be decreased by helping abstinent patients to perceive time-duration of an abstinence/withdrawal period precisely.

Parietal contributions to visual feature binding: evidence from a patient with bilateral lesions.

SR Friedman-Hill — 2006-11-11T18:35:50-00:00

Science, Vol. 269, No. 5225. (11 August 1995), pp. 853-855.

Neurophysiologists have documented the existence of multiple cortical areas responsive to different visual features. This modular organization has sparked theoretical interest in how the "binding problem" is solved. Recent data from a neurological patient (R.M.) with bilateral parietal-occipital lesions demonstrates that the binding problem is not just a hypothetical construct; it can be a practical problem, as rare as the selective inability to perceive motion or color. R.M. miscombines colors and shapes even under free viewing conditions and is unable to judge either relative or absolute visual locations. The evidence suggests that a single explanation--an inadequate spatial representation--can account for R.M.'s spatial judgment and feature-binding deficits.

Posterior parietal cortex and the filtering of distractors.

SR Friedman-Hill — 2006-06-13T01:59:00-00:00

Proc Natl Acad Sci U S A, Vol. 100, No. 7. (1 April 2003), pp. 4263-4268.

Neural systems for visual processing can focus attention on behaviorally relevant objects, filtering out competing distractors. Neurophysiological studies in animals and brain imaging studies in humans suggest that such filtering depends on top-down inputs to extrastriate visual areas, originating in structures important for attentional control. To test whether the posterior parietal cortex may be a necessary source of signals that filter distractors, we measured the ability of a patient with bilateral parietal lesions to discriminate the features of a target surrounded by distractors of variable contrast. In the presence of distractors, the patient was impaired at discriminating both grating orientation and faces, and the magnitude of the impairment increased with distractor salience. These attentional deficits are remarkably similar to those caused by damage to monkey extrastriate regions V4 andor TEO, which are thought to be recipients of top-down attentional feedback. In contrast to the effects of V4 and TEO lesions, however, the parietal lesions impaired performance even with widely spaced targets and distractors, a finding consistent with the projections of parietal cortex to visual processing areas covering a wide range of receptive field sizes and eccentricities.

The human orbitofrontal cortex: linking reward to hedonic experience

Morten Kringelbach — 2005-09-01T16:26:05-00:00

Nature Reviews Neuroscience, Vol. 6, No. 9. (01 September 2005), pp. 691-702.

Activity in human ventral striatum locked to errors of reward prediction.

G Pagnoni — 2006-08-17T13:08:44-00:00

Nat Neurosci, Vol. 5, No. 2. (February 2002), pp. 97-98.

The mesolimbic dopaminergic system has long been known to be involved in the processing of rewarding stimuli, although recent evidence from animal research has suggested a more specific role of signaling errors in the prediction of rewards. We tested this hypothesis in humans, using functional magnetic resonance imaging (fMRI) and an operant conditioning paradigm for the discrete delivery of small quantities of fruit juice, along with a control experiment in which juice was substituted with a neutral visual stimulus. A local estimation of the activity in the ventral striatum showed a significant differentiation when the juice was withheld at the expected time of delivery; this finding was not replicated in the case of visual stimulation, providing evidence for time-locked processing of reward prediction errors in human ventral striatum.

Frames, biases, and rational decision-making in the human brain.

B De Martino — 2006-08-07T22:43:13-00:00

Science, Vol. 313, No. 5787. (4 August 2006), pp. 684-687.

Human choices are remarkably susceptible to the manner in which options are presented. This so-called "framing effect" represents a striking violation of standard economic accounts of human rationality, although its underlying neurobiology is not understood. We found that the framing effect was specifically associated with amygdala activity, suggesting a key role for an emotional system in mediating decision biases. Moreover, across individuals, orbital and medial prefrontal cortex activity predicted a reduced susceptibility to the framing effect. This finding highlights the importance of incorporating emotional processes within models of human choice and suggests how the brain may modulate the effect of these biasing influences to approximate rationality.

Decoding the visual and subjective contents of the human brain

Yukiyasu Kamitani — 2005-04-26T18:40:18-00:00

Nature Neuroscience, Vol. 8, No. 5. (24 April 2005), pp. 679-685.

Essay: Forty-five years of split-brain research and still going strong

Michael Gazzaniga — 2005-08-01T21:26:44-00:00

Nature Reviews Neuroscience, Vol. 6, No. 8. (01 August 2005), pp. 653-659.

On Making the Right Choice: The Deliberation-Without-Attention Effect

Ap Dijksterhuis — 2006-02-17T17:51:40-00:00

Science, Vol. 311, No. 5763. (17 February 2006), pp. 1005-1007.

Contrary to conventional wisdom, it is not always advantageous to engage in thorough conscious deliberation before choosing. On the basis of recent insights into the characteristics of conscious and unconscious thought, we tested the hypothesis that simple choices (such as between different towels or different sets of oven mitts) indeed produce better results after conscious thought, but that choices in complex matters (such as between different houses or different cars) should be left to unconscious thought. Named the "deliberation-without-attention" hypothesis, it was confirmed in four studies on consumer choice, both in the laboratory as well as among actual shoppers, that purchases of complex products were viewed more favorably when decisions had been made in the absence of attentive deliberation.

Selection and Maintenance of Saccade Goals in the Human Frontal Eye Fields.

Clayton E Curtis — 2006-02-11T09:25:27-00:00

J Neurophysiol (8 February 2006)

In a delayed-response task, response selection marks an important transition from sensory to motor processing. Using event-related fMRI, we imaged the human brain during performance of a novel delayed-saccade task that isolated response selection from visual encoding and motor execution. The frontal eye-fields (FEF) and intraparietal sulcus (IPS) both showed robust contra-lateralized activity time-locked to response selection. Moreover, response selection affected delay-period activity differently in these regions; it persisted throughout the memory delay period following response selection in the FEF, but not IPS. Our results indicate that the FEF and IPS both make important but distinct contributions to spatial working memory. The mechanism that the FEF uses to support spatial working memory is tied to the selection and prospective coding of saccade goals, while the role of the IPS may be more tied to retrospective coding of sensory representations.

Toward a behavioral economic understanding of drug dependence: delay discounting processes.

WK Bickel — 2006-06-08T18:42:24-00:00

Addiction, Vol. 96, No. 1. (January 2001), pp. 73-86.

Behavioral economics examines conditions that influence the consumption of commodities and provides several concepts that may be instrumental in understanding drug dependence. One such concept of significance is that of how delayed reinforcers are discounted by drug dependent individuals. Discounting of delayed reinforcers refers to the observation that the value of a delayed reinforcer is discounted (reduced in value or considered to be worth less) compared to the value of an immediate reinforcer. This paper examines how delay discounting may provide an explanation of both impulsivity and loss of control exhibited by the drug dependent. In so doing, the paper reviews economic models of delay discounting, the empirical literature on the discounting of delayed reinforcers by the drug dependent and the scientific literature on personality assessments of impulsivity among drug-dependent individuals. Finally, future directions for the study of discounting are discussed, including the study of loss of control and loss aversion among drug-dependent individuals, the relationship of discounting to both the behavioral economic measure of elasticity as well as to outcomes observed in clinical settings, and the relationship between impulsivity and psychological disorders other than drug dependence.

The present values of delayed rewards are approximately additive.

KN Kirby — 2006-05-16T17:02:14-00:00

Behav Processes, Vol. 72, No. 3. (1 June 2006), pp. 273-282.

In two experiments, human subjects were asked to estimate their present values of single delayed rewards and their present values of temporal sequences of three rewards. Present values were solicited by asking subjects to indicate an amount of money v for which they would be indifferent between receiving v at the end of the session and receiving the delayed reward(s). A procedure was used for which responding the true value of v was the optimal strategy, and the actual payoff that each subject received was determined by one randomly selected trial. In Experiment 1 (n=29) each delayed reward was $9.90 in cash. In Experiment 2 (n=19) the delayed rewards were dated $15 gift certificates to a local restaurant. In both experiments, the present values of the sequences were approximately equal to the sums of the present values of their component rewards. The presence of outliers suggests that a few subjects may have valued sequences less than the sums of their single rewards. Effects of a preference for uniform sequences, if any, were too small to be detected. Discounting of sequences was well fit by a parallel hyperbolic discounting equation, consistent with Mazur's [Mazur, J.E., 1986. Choice between single and multiple delayed reinforcers. J. Exp. Anal. Behav. 46 (1), 67-77] results using multiple reinforcers.

Stimulus probability directs spatial attention: an enhancement of sensitivity in humans and monkeys.

VM Ciaramitaro — 2005-02-22T21:48:25-00:00

Vision Res, Vol. 41, No. 1. (January 2001), pp. 57-75.

We examined whether improvements in sensory processing, defined as changes in sensitivity, could be elicited in a simple luminance discrimination task without eliciting concomitant changes in decision processing. To this end we developed a task, for use in both humans and monkeys, in which prior knowledge about where a discriminative stimulus was likely to appear (1) offered no decisional advantage in solving our task and (2) could be parametrically varied to yield a psychometric function. We found that if we parametrically varied the quality of prior knowledge, by increasing the probability, and thus the certainty, that a discriminative stimulus would appear at a particular location under these conditions, luminance discrimination improved for both human and monkey subjects. This improvement was correlated with an enhancement in sensory processing, but not with any systematic changes in decisional processing, as assessed by signal detection theory. These results suggest that (1) sensory processing and decision processing can be separated by task design and (2) systematic changes in prior knowledge about where a stimulus may appear can lead to systematic changes in sensitivity; providing a psychometric function for the influence of prior knowledge on perceptual sensitivity. Importantly, these results were obtained from both human and monkey subjects. Similar task designs could be used in physiological studies attempting to generate linking hypotheses between psychometric and neurometric functions, ultimately allowing changes in perceptual sensitivity to be linked to changes in an underlying neural substrate.

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.

Operant variability: evidence, functions, and theory.

A Neuringer — 2006-01-24T17:21:51-00:00

Psychon Bull Rev, Vol. 9, No. 4. (December 2002), pp. 672-705.

Although responses are sometimes easy to predict, at other times responding seems highly variable, unpredictable, or even random. The inability to predict is generally attributed to ignorance of controlling variables, but this article is a review of research showing that the highest levels of behavioral variability may result from identifiable reinforcers contingent on such variability. That is, variability is an operant. Discriminative stimuli and reinforcers control it, resulting in low or high variability, depending on the contingencies. Schedule-of-reinforcement effects are orderly, and choosing to vary or repeat is lawfully governed by relative reinforcement frequencies. The operant nature of variability has important implications. For example, learning, exploring, creating, and problem solving may partly depend on it. Abnormal levels of variability, including those found in psychopathologies such as autism, depression, and attention deficit hyperactivity disorder, may be modified through reinforcement. Operant variability may also help to explain some of the unique attributes of voluntary action.

Predictive neural coding of reward preference involves dissociable responses in human ventral midbrain and ventral striatum.

JP O'doherty — 2006-01-18T01:28:49-00:00

Neuron, Vol. 49, No. 1. (5 January 2006), pp. 157-166.

Food preferences are acquired through experience and can exert strong influence on choice behavior. In order to choose which food to consume, it is necessary to maintain a predictive representation of the subjective value of the associated food stimulus. Here, we explore the neural mechanisms by which such predictive representations are learned through classical conditioning. Human subjects were scanned using fMRI while learning associations between arbitrary visual stimuli and subsequent delivery of one of five different food flavors. Using a temporal difference algorithm to model learning, we found predictive responses in the ventral midbrain and a part of ventral striatum (ventral putamen) that were related directly to subjects' actual behavioral preferences. These brain structures demonstrated divergent response profiles, with the ventral midbrain showing a linear response profile with preference, and the ventral striatum a bivalent response. These results provide insight into the neural mechanisms underlying human preference behavior.

Temporal discounting when the choice is between two delayed rewards.

L Green — 2005-11-02T16:38:39-00:00

J Exp Psychol Learn Mem Cogn, Vol. 31, No. 5. (September 2005), pp. 1121-1133.

The present experiments extend the temporal discounting paradigm from choice between an immediate and a delayed reward to choice between 2 delayed rewards: a smaller amount of money available sooner and a larger amount available later. Across different amounts and delays, the data were consistently well described by a hyperbola-like discounting function, and the degree of discounting decreased systematically as the delay to the sooner reward increased. Three theoretical models (the elimination-by-aspects, present-value comparison, and common-aspect attenuation hypotheses) were evaluated. The best account of the data was provided by the common-aspect attenuation hypothesis, according to which the common aspect of the choice alternatives (i.e., the time until the sooner reward is available) receives less weight in the decision-making process. ((c) 2005 APA, all rights reserved).

Topographic organization for delayed saccades in human posterior parietal cortex.

D Schluppeck — 2005-10-12T15:56:33-00:00

J Neurophysiol, Vol. 94, No. 2. (August 2005), pp. 1372-1384.

Posterior parietal cortex (PPC) is thought to play a critical role in decision making, sensory attention, motor intention, and/or working memory. Research on the PPC in non-human primates has focused on the lateral intraparietal area (LIP) in the intraparietal sulcus (IPS). Neurons in LIP respond after the onset of visual targets, just before saccades to those targets, and during the delay period in between. To study the function of posterior parietal cortex in humans, it will be crucial to have a routine and reliable method for localizing specific parietal areas in individual subjects. Here, we show that human PPC contains at least two topographically organized regions, which are candidates for the human homologue of LIP. We mapped the topographic organization of human PPC for delayed (memory guided) saccades using fMRI. Subjects were instructed to fixate centrally while a peripheral target was briefly presented. After a further 3-s delay, subjects made a saccade to the remembered target location followed by a saccade back to fixation and a 1-s inter-trial interval. Targets appeared at successive locations "around the clock" (same eccentricity, approximately 30 degrees angular steps), to produce a traveling wave of activity in areas that are topographically organized. PPC exhibited topographic organization for delayed saccades. We defined two areas in each hemisphere that contained topographic maps of the contra-lateral visual field. These two areas were immediately rostral to V7 as defined by standard retinotopic mapping. The two areas were separated from each other and from V7 by reversals in visual field orientation. However, we leave open the possibility that these two areas will be further subdivided in future studies. Our results demonstrate that topographic maps tile the cortex continuously from V1 well into PPC.

Breakdown of cortical effective connectivity during sleep.

M Massimini — 2005-10-04T15:32:39-00:00

Science, Vol. 309, No. 5744. (30 September 2005), pp. 2228-2232.

When we fall asleep, consciousness fades yet the brain remains active. Why is this so? To investigate whether changes in cortical information transmission play a role, we used transcranial magnetic stimulation together with high-density electroencephalography and asked how the activation of one cortical area (the premotor area) is transmitted to the rest of the brain. During quiet wakefulness, an initial response (approximately 15 milliseconds) at the stimulation site was followed by a sequence of waves that moved to connected cortical areas several centimeters away. During non-rapid eye movement sleep, the initial response was stronger but was rapidly extinguished and did not propagate beyond the stimulation site. Thus, the fading of consciousness during certain stages of sleep may be related to a breakdown in cortical effective connectivity.

The functional organization of the intraparietal sulcus in humans and monkeys

Christian Grefkes — 2005-07-06T02:56:42-00:00

Journal of Anatomy, Vol. 207, No. 1. (July 2005), pp. 3-17.

Saccadic eye movements cause compression of time as well as space

Concetta Morrone — 2005-07-01T19:24:04-00:00

Nature Neuroscience, Vol. 8, No. 7. (19 June 2005), pp. 950-954.

Oxytocin increases trust in humans

Michael Kosfeld — 2005-06-01T20:03:07-00:00

Nature, Vol. 435, No. 7042., pp. 673-676.

Trust pervades human societies. Trust is indispensable in friendship, love, families and organizations, and plays a key role in economic exchange and politics. In the absence of trust among trading partners, market transactions break down. In the absence of trust in a country's institutions and leaders, political legitimacy breaks down. Much recent evidence indicates that trust contributes to economic, political and social success. Little is known, however, about the biological basis of trust among humans. Here we show that intranasal administration of oxytocin, a neuropeptide that plays a key role in social attachment and affiliation in non-human mammals, causes a substantial increase in trust among humans, thereby greatly increasing the benefits from social interactions. We also show that the effect of oxytocin on trust is not due to a general increase in the readiness to bear risks. On the contrary, oxytocin specifically affects an individual's willingness to accept social risks arising through interpersonal interactions. These results concur with animal research suggesting an essential role for oxytocin as a biological basis of prosocial approach behaviour.

Saccades exhibit abrupt transition between reactive and predictive; predictive saccade sequences have long-term correlations.

M Shelhamer — 2005-06-08T21:01:24-00:00

J Neurophysiol, Vol. 90, No. 4. (October 2003), pp. 2763-2769.

To compensate for neural delays, organisms require predictive motor control. We investigated the transition between reaction and prediction in saccades (rapid eye movements) to periodically paced targets. Tracking at low frequencies (0.2-0.3 Hz) is reactive (eyes lag target) and at high frequencies (0.9-1.0 Hz) is predictive (eyes anticipate target); there is an abrupt rather than smooth transition between the two modes (a "phase transition," as found in bistable physical systems). These behaviors represent stable modes of the oculomotor control system, with attendant rapid switching between the neural pathways underlying the different modes. Furthermore, predictive saccades exhibit long-term correlations (slow decay of the autocorrelation function, manifest as a 1/f alpha spectrum). This indicates that predictive trials are not independent. The findings have implications for the understanding of predictive motor control: predictive performance during a given trial is influenced by a feedback process that takes into account the latency of previous trials.

Sequences of predictive saccades are correlated over a span of approximately 2 s and produce a fractal time series.

M Shelhamer — 2005-06-07T16:04:26-00:00

J Neurophysiol, Vol. 93, No. 4. (April 2005), pp. 2002-2011.

We previously demonstrated that there is an abrupt (rather than smooth) transition between reactive and predictive modes of eye-movement tracking of target lights (a phase transition). We also found evidence that the sequence of eye movements in the reactive mode was independent, whereas those in the predictive mode were correlated and possibly formed a random fractal sequence. Here we confirm the finding of fractal structure by quantifying the rate of decay of nonlinear forecasting when applied to these data. We also estimate the window over which consecutive trials are correlated and show that the duration of this window is fixed in time rather than number of trials. These results have implications for the neural mechanisms that drive predictive movements.

A general mechanism for perceptual decision-making in the human brain

HR Heekeren — 2005-03-14T22:15:51-00:00

Nature, Vol. 431, No. 7010. (14 October 2004), pp. 859-862.

Scalar expectancy theory and peak-interval timing in humans.

BC Rakitin — 2005-03-13T20:17:17-00:00

J Exp Psychol Anim Behav Process, Vol. 24, No. 1. (January 1998), pp. 15-33.

The properties of the internal clock, temporal memory, and decision processes used to time short durations were investigated. The peak-interval procedure was used to evaluate the timing of 8-, 12-, and 21-s intervals, and analyses were conducted on the mean response functions and on individual trials. A distractor task prevented counting, and visual feedback on accuracy and precision was provided after each trial. Mean response distributions were (a) centered at the appropriate real-time criteria, (b) highly symmetrical, and (c) scalar in their variability. Analysis of individual trials indicated more memory variability relative to response threshold variability. Taken together, these results demonstrate that humans show the same qualitative timing properties that other animals do, but with some quantitative differences.

A neuroeconomics approach to inferring utility functions in sensorimotor control.

KP Körding — 2005-02-02T22:42:31-00:00

PLoS Biol, Vol. 2, No. 10. (October 2004)

Making choices is a fundamental aspect of human life. For over a century experimental economists have characterized the decisions people make based on the concept of a utility function. This function increases with increasing desirability of the outcome, and people are assumed to make decisions so as to maximize utility. When utility depends on several variables, indifference curves arise that represent outcomes with identical utility that are therefore equally desirable. Whereas in economics utility is studied in terms of goods and services, the sensorimotor system may also have utility functions defining the desirability of various outcomes. Here, we investigate the indifference curves when subjects experience forces of varying magnitude and duration. Using a two-alternative forced-choice paradigm, in which subjects chose between different magnitude-duration profiles, we inferred the indifference curves and the utility function. Such a utility function defines, for example, whether subjects prefer to lift a 4-kg weight for 30 s or a 1-kg weight for a minute. The measured utility function depends nonlinearly on the force magnitude and duration and was remarkably conserved across subjects. This suggests that the utility function, a central concept in economics, may be applicable to the study of sensorimotor control.

Prediction of immediate and future rewards differentially recruits cortico-basal ganglia loops.

SC Tanaka — 2005-03-09T19:40:59-00:00

Nat Neurosci, Vol. 7, No. 8. (August 2004), pp. 887-893.

Evaluation of both immediate and future outcomes of one's actions is a critical requirement for intelligent behavior. Using functional magnetic resonance imaging (fMRI), we investigated brain mechanisms for reward prediction at different time scales in a Markov decision task. When human subjects learned actions on the basis of immediate rewards, significant activity was seen in the lateral orbitofrontal cortex and the striatum. When subjects learned to act in order to obtain large future rewards while incurring small immediate losses, the dorsolateral prefrontal cortex, inferior parietal cortex, dorsal raphe nucleus and cerebellum were also activated. Computational model-based regression analysis using the predicted future rewards and prediction errors estimated from subjects' performance data revealed graded maps of time scale within the insula and the striatum: ventroanterior regions were involved in predicting immediate rewards and dorsoposterior regions were involved in predicting future rewards. These results suggest differential involvement of the cortico-basal ganglia loops in reward prediction at different time scales.