Neural coding of reward magnitude in the orbitofrontal cortex of the rat during a five-odor olfactory discrimination task

The orbitofrontal cortex (OBFc) has been suggested to code the motivational value of environmental stimuli and to use this information for the flexible guidance of goal-directed behavior. To examine whether information regarding reward prediction is quantitatively represented in the rat OBFc, neural activity was recorded during an olfactory discrimination "go"/"no-go" task in which five different odor stimuli were predictive for various amounts of reward or an aversive reinforcer. Neural correlates related to both actual and expected reward magnitude were observed. Responses related to reward expectation occurred during the execution of the behavioral response toward the reward site and within a waiting period prior to reinforcement delivery. About one-half of these neurons demonstrated differential firing toward the different reward sizes. These data provide new and strong evidence that reward expectancy, regardless of reward magnitude, is coded by neurons of the rat OBFc, and are indicative for representation of quantitative information concerning expected reward. Moreover, neural correlates of reward expectancy appear to be distributed across both motor and nonmotor phases of the task.

van Duuren, Esther, Escamez, Francisco A. Nieto, Joosten, Ruud N.J.M.A., Visser, Rein, Mulder, Antonius B., Pennartz, Cyriel M.A.
Neural coding of reward magnitude in the orbitofrontal cortex of the rat during a five-odor olfactory discrimination task.
Learn. Mem. 2007 14: 446-456.

http://www.learnmem.org/cgi/content/abstract/14/6/446

Associative Encoding in Anterior Piriform Cortex versus Orbitofrontal Cortex during Odor Discrimination and Reversal Learning

Recent proposals have conceptualized piriform cortex as an association cortex, capable of integrating incoming olfactory information with descending input from higher order associative regions such as orbitofrontal cortex (OFC). If true, encoding in piriform cortex should reflect associative features prominent in these areas during associative learning involving olfactory cues. To test this hypothesis, we recorded from neurons in OFC and anatomically related parts of the anterior piriform cortex (APC) in rats, learning and reversing novel odor discriminations. Findings in OFC were similar to what we have reported previously, with nearly all the cue-selective neurons exhibiting substantial plasticity during learning and reversal. Also, many of the cue-selective neurons were originally responsive in anticipation of the outcomes early in learning, thereby providing a single-unit representation of the cue-outcome associations. Some of these features were also evident in firing activity in APC, including some plasticity across learning and reversal. However, APC neurons failed to reverse cue selectivity when the associated outcome was changed, and the cue-selective population did not include neurons that were active prior to outcome delivery. Thus, although representations in APC are substantially more associative than expected in a purely sensory region, they do appear to be somewhat more constrained by the sensory features of the odor cues than representations in downstream areas of OFC.

Matthew R. Roesch , Thomas A. Stalnaker , and Geoffrey Schoenbaum.
Associative Encoding in Anterior Piriform Cortex versus Orbitofrontal Cortex during Odor Discrimination and Reversal Learning.
Cerebral Cortex Advance Access published on March 1, 2007, DOI 10.1093/cercor/bhk009. Cereb. Cortex 17: 643-652.

http://cercor.oxfordjournals.org/cgi/content/abstract/17/3/643

From Rule to Response: Neuronal Processes in the Premotor and Prefrontal Cortex

The ability to use abstract rules or principles allows behavior to generalize from specific circumstances (e.g., rules learned in a specific restaurant can subsequently be applied to any dining experience). Neurons in the prefrontal cortex (PFC) encode such rules. However, to guide behavior, rules must be linked to motor responses. We investigated the neuronal mechanisms underlying this process by recording from the PFC and the premotor cortex (PMC) of monkeys trained to use two abstract rules: "same" or "different." The monkeys had to either hold or release a lever, depending on whether two successively presented pictures were the same or different, and depending on which rule was in effect. The abstract rules were represented in both regions, although they were more prevalent and were encoded earlier and more strongly in the PMC. There was a perceptual bias in the PFC, relative to the PMC, with more PFC neurons encoding the presented pictures. In contrast, neurons encoding the behavioral response were more prevalent in the PMC, and the selectivity was stronger and appeared earlier in the PMC than in the PFC.

Jonathan D. Wallis, and Earl K. Miller.
From Rule to Response: Neuronal Processes in the Premotor and Prefrontal Cortex.
Neurophysiol 90: 1790-1806, 2003. First published doi:10.1152/jn.00086.2003.

http://jn.physiology.org/cgi/content/full/90/3/1790/

Integrating Orbitofrontal Cortex into Prefrontal Theory: Common Processing Themes across Species and Subdivisions

Currently, many theories highlight either representational memory or rule representation as the hallmark of prefrontal function. Neurophysiological findings in the primate dorsolateral prefrontal cortex indicate that both features may characterize prefrontal processing. Neurons in the dorsolateral prefrontal cortex encode information in working memory, and this information is represented when relevant to the rules governing performance in a task. In this review, we discuss recent reports of encoding in primate and rat orbitofrontal regions indicating that these features also characterize activity in the orbitofrontal subdivision of the prefrontal cortex. These data indicate that (1) neural activity in the orbitofrontal cortex links the current incentive value of reinforcers to cues, rather than representing the physical features of cues or associated reinforcers; (2) this incentive-based information is represented in the orbitofrontal cortex when it is relevant to the rules guiding performance in a task; and (3) incentive information is also represented in the orbitofrontal cortex in working memory during delays when neither the cues nor reinforcers are present. Therefore, although the orbitofrontal cortex appears to be uniquely specialized to process incentive or motivational information, it may be integrated into a more global framework of prefrontal function characterized by representational encoding of performance-relevant information.

Schoenbaum, Geoffrey, Setlow, Barry
Integrating Orbitofrontal Cortex into Prefrontal Theory: Common Processing Themes across Species and Subdivisions
Learn. Mem. 2001 8: 134-147

http://www.learnmem.org/cgi/content/full/8/3/134

An attractor network in the hippocampus: Theory and neurophysiology

A quantitative computational theory of the operation of the CA3 system as an attractor or autoassociation network is described. Based on the proposal that CA3–CA3 autoassociative networks are important for episodic or event memory in which space is a component (place in rodents and spatial view in primates), it has been shown behaviorally that the CA3 supports spatial rapid one-trial learning and learning of arbitrary associations and pattern completion where space is a component. Consistent with the theory, single neurons in the primate CA3 respond to combinations of spatial view and object, and spatial view and reward. Furthermore, single CA3 neurons reflect the recall of a place from an object in a one-trial object-place event memory task. CA3 neurons also reflect in their firing a memory of spatial view that is retained and updated by idiothetic information to implement path integration when the spatial view is obscured. Based on the computational proposal that the dentate gyrus produces sparse representations by competitive learning and via the mossy fiber pathway forces new representations on the CA3 during learning (encoding), it has been shown behaviorally that the dentate gyrus supports spatial pattern separation during learning, and that the mossy fiber system to CA3 connections are involved in learning but not in recall. The perforant path input to CA3 is quantitatively appropriate to provide the cue for recall in CA3. The concept that the CA1 recodes information from CA3 and sets up associatively learned back-projections to neocortex to allow subsequent retrieval of information to neocortex provides a quantitative account of the large number of hippocampo–neocortical back-projections.

Rolls, Edmund T.
An attractor network in the hippocampus: Theory and neurophysiology
Learn. Mem. 2007 14: 714-731.

http://www.learnmem.org/cgi/content/abstract/14/11/714

Specific Involvement of Human Parietal Systems and the Amygdala in the Perception of Biological Motion

To explore the extent to which functional systems within the human posterior parietal cortex and the superior temporal sulcus are involved in the perception of action, we measured cerebral metabolic activity in human subjects by positron emission tomography during the perception of simulations of biological motion with point-light displays. The experimental design involved comparisons of activity during the perception of goal-directed hand action, whole body motion, object motion, and random motion. The results demonstrated that the perception of scripts of goal-directed hand action implicates the cortex in the intraparietal sulcus and the caudal part of the superior temporal sulcus, both in the left hemisphere. By contrast, the rostrocaudal part of the right superior temporal sulcus and adjacent temporal cortex, and limbic structures such as the amygdala, are involved in the perception of signs conveyed by expressive body movements.

Eva Bonda, Michael Petrides, David Ostry, and Alan Evans
Specific Involvement of Human Parietal Systems and the Amygdala in the Perception of Biological Motion
J. Neurosci. 16: 3737-3744; doi:

http://www.jneurosci.org/cgi/content/full/16/11/3737

Orbitofrontal Cortex Encodes Willingness to Pay in Everyday Economic Transactions

An essential component of every economic transaction is a willingness-to-pay (WTP) computation in which buyers calculate the maximum amount of financial resources that they are willing to give up in exchange for the object being sold. Despite its pervasiveness, little is known about how the brain makes this computation. We investigated the neural basis of the WTP computation by scanning hungry subjects' brains using functional magnetic resonance imaging while they placed real bids for the right to eat different foods. We found that activity in the medial orbitofrontal cortex and in the dorsolateral prefrontal cortex encodes subjects' WTP for the items. Our results support the hypothesis that the medial orbitofrontal cortex encodes the value of goals in decision making.

Hilke Plassmann, John O'Doherty, and Antonio Rangel
Orbitofrontal Cortex Encodes Willingness to Pay in Everyday Economic Transactions
J. Neurosci. 27: 9984-9988; doi:10.1523/JNEUROSCI.2131-07.2007

http://www.jneurosci.org/cgi/content/abstract/27/37/9984