Reward modulates neuronal activity in the hippocampus of the rat

In vivo structural connectivity of the reward system along the hippocampal long axis

Recent work has identified a critical role for the hippocampus in reward-sensitive behaviors, including motivated memory, reinforcement learning, and decision-making. Animal histology and human functional neuroimaging have shown that brain regions involved in reward processing and motivation are more interconnected with the ventral/anterior hippocampus. However, direct evidence examining gradients of structural connectivity between reward regions and the hippocampus in humans is lacking. The present study used diffusion MRI (dMRI) and probabilistic tractography to quantify the structural connectivity of the hippocampus with key reward processing regions in vivo. Using a large sample of subjects (N = 628) from the human connectome dMRI data release, we found that connectivity profiles with the hippocampus varied widely between different regions of the reward circuit. While the dopaminergic midbrain (ventral tegmental area) showed stronger connectivity with the anterior versus posterior hippocampus, the ventromedial prefrontal cortex showed stronger connectivity with the posterior hippocampus. The limbic (ventral) striatum demonstrated a more homogeneous connectivity profile along the hippocampal long axis. This is the first study to generate a probabilistic atlas of the hippocampal structural connectivity with reward-related networks, which is essential to investigating how these circuits contribute to normative adaptive behavior and maladaptive behaviors in psychiatric illness. These findings describe nuanced structural connectivity that sets the foundation to better understand how the hippocampus influences reward-guided behavior in humans.

Contextual memory engrams, and the neuromodulatory influence of the locus coeruleus

Here, we review the basis of contextual memory at a conceptual and cellular level. We begin with an overview of the philosophical foundations of traversing space, followed by theories covering the material bases of contextual representations in the hippocampus (engrams), exploring functional characteristics of the cells and subfields within. Next, we explore various methodological approaches for investigating contextual memory engrams, emphasizing plasticity mechanisms. This leads us to discuss the role of neuromodulatory inputs in governing these dynamic changes. We then outline a recent hypothesis involving noradrenergic and dopaminergic projections from the locus coeruleus (LC) to different subregions of the hippocampus, in sculpting contextual representations, giving a brief description of the neuroanatomical and physiological properties of the LC. Finally, we examine how activity in the LC influences contextual memory processes through synaptic plasticity mechanisms to alter hippocampal engrams. Overall, we find that phasic activation of the LC plays an important role in promoting new learning and altering mnemonic processes at the behavioral and cellular level through the neuromodulatory influence of NE/DA in the hippocampus. These findings may provide insight into mechanisms of hippocampal remapping and memory updating, memory processes that are potentially dysregulated in certain psychiatric and neurodegenerative disorders.

Hippocampal spatial view cells for memory and navigation, and their underlying connectivity in humans

Hippocampal and parahippocampal gyrus spatial view neurons in primates respond to the spatial location being looked at. The representation is allocentric, in that the responses are to locations "out there" in the world, and are relatively invariant with respect to retinal position, eye position, head direction, and the place where the individual is located. The underlying connectivity in humans is from ventromedial visual cortical regions to the parahippocampal scene area, leading to the theory that spatial view cells are formed by combinations of overlapping feature inputs self-organized based on their closeness in space. Thus, although spatial view cells represent "where" for episodic memory and navigation, they are formed by ventral visual stream feature inputs in the parahippocampal gyrus in what is the parahippocampal scene area. A second "where" driver of spatial view cells are parietal inputs, which it is proposed provide the idiothetic update for spatial view cells, used for memory recall and navigation when the spatial view details are obscured. Inferior temporal object "what" inputs and orbitofrontal cortex reward inputs connect to the human hippocampal system, and in macaques can be associated in the hippocampus with spatial view cell "where" representations to implement episodic memory. Hippocampal spatial view cells also provide a basis for navigation to a series of viewed landmarks, with the orbitofrontal cortex reward inputs to the hippocampus providing the goals for navigation, which can then be implemented by hippocampal connectivity in humans to parietal cortex regions involved in visuomotor actions in space. The presence of foveate vision and the highly developed temporal lobe for object and scene processing in primates including humans provide a basis for hippocampal spatial view cells to be key to understanding episodic memory in the primate and human hippocampus, and the roles of this system in primate including human navigation.

Septotemporal variations in hippocampal value and outcome processing

A large body of evidence indicates functional variations along the hippocampal longitudinal axis. To investigate whether and how value and outcome processing vary between the dorsal (DH) and the ventral hippocampus (VH), we examined neuronal activity and inactivation effects of the DH and VH in mice performing probabilistic classical conditioning tasks. Inactivation of either structure disrupts value-dependent anticipatory licking, and value-coding neurons are found in both structures, indicating their involvement in value processing. However, the DH neuronal population increases activity as a function of value, while the VH neuronal population is preferentially responsive to the highest-value sensory cue. Also, signals related to outcome-dependent value learning are stronger in the DH. VH neurons instead show rapid responses to punishment and strongly biased responses to negative prediction error. These findings suggest that the DH faithfully represents the external value landscape, whereas the VH preferentially represents behaviorally relevant, salient features of experienced events.

Neural circuit dynamics of drug-context associative learning in the mouse hippocampus

The environmental context associated with previous drug consumption is a potent trigger for drug relapse. However, the mechanism by which neural representations of context are modified to incorporate information associated with drugs of abuse remains unknown. Using longitudinal calcium imaging in freely behaving mice, we find that unlike the associative learning of natural reward, drug-context associations for psychostimulants and opioids are encoded in a specific subset of hippocampal neurons. After drug conditioning, these neurons weakened their spatial coding for the non-drug paired context, resulting in an orthogonal representation for the drug versus non-drug context that was predictive of drug-seeking behavior. Furthermore, these neurons were selected based on drug-spatial experience and were exclusively tuned to animals' allocentric position. Together, this work reveals how drugs of abuse alter the hippocampal circuit to encode drug-context associations and points to the possibility of targeting drug-associated memory in the hippocampus.

The mediating effect of geospatial thinking on the relationship between family capital and sense of place

Few studies have examined how family capital affects the sense of place, and the effect of spatial thinking on the relationship between the two is unclear. This study constructs a mediation model to examine the impact of family capital on sense of place and the mediation effect of geospatial thinking. A total of 1,004 upper-secondary-school students were surveyed using the Family Capital Questionnaire, the Geospatial Thinking Test, and the Sense of Place Scale. The correlation analysis showed that family capital has a positive effect on both sense of place and geospatial thinking. Moreover, there is also a significant positive correlation between geospatial thinking and sense of place. The results of mediation analysis indicated that geospatial thinking plays mediating and buffering roles in the relationship between family capital and sense of place after controlling for gender and residential address. The direct and indirect effects accounted for 73.31 and 26.69% of the total effect, respectively. Specifically, family capital is a significant positive predictor of both sense of place and geospatial thinking, and geospatial thinking partially mediates the relationship between family capital and sense of place. Students from better family backgrounds are more likely to have a better geospatial thinking and sense of place, as well as geospatial thinking promotes the development of a sense of place. Therefore, both family capital and geospatial thinking should be considered when we want to examine and develop individuals’ level of sense of place.

Neurons in the Human Left Amygdala Automatically Encode Subjective Value Irrespective of Task

The amygdala plays an important role in the computation of internal reward signals. In animals it has been shown to enable a stimulus to indicate the current value of a reinforcer. However, the exact nature of the current value representations in humans remains unknown. Specifically, do neurons of the human amygdala represent current value signals only in tasks requiring valuation? We recorded from 406 neurons in the amygdala, orbitofrontal cortex, parahippocampal cortex, entorhinal cortex, and hippocampus of 6 neurosurgical patients while subjects repeatedly viewed 40 different pictures of sweet or salty "junk food" items in 2 different tasks. Neural activity during stimulus inspection in a valuation task reflected food preferences in the amygdala, orbitofrontal cortex, hippocampus, and entorhinal cortex. Notably, only left amygdala activity represented these food preferences even in a sweet-salty classification task. Valuation signals of the left amygdala thus appear to be stimulus-, not-task driven.

The hippocampus encodes delay and value information during delay-discounting decision making

The hippocampus, a region critical for memory and spatial navigation, has been implicated in delay discounting, the decline in subjective reward value when a delay is imposed. However, how delay information is encoded in the hippocampus is poorly understood. Here, we recorded from CA1 of mice performing a delay-discounting decision-making task, where delay lengths, delay positions, and reward amounts were changed across sessions, and identified subpopulations of CA1 neurons that increased or decreased their firing rate during long delays. The activity of both delay-active and -suppressed cells reflected delay length, delay position, and reward amount; but manipulating reward amount differentially impacted the two populations, suggesting distinct roles in the valuation process. Further, genetic deletion of the N-methyl-D-aspartate (NMDA) receptor in hippocampal pyramidal cells impaired delay-discount behavior and diminished delay-dependent activity in CA1. Our results suggest that distinct subclasses of hippocampal neurons concertedly support delay-discounting decisions in a manner that is dependent on NMDA receptor function.

Multiplexing of Information about Self and Others in Hippocampal Ensembles

In addition to coding a subject's location in space, the hippocampus has been suggested to code social information, including the spatial position of conspecifics. "Social place cells" have been reported for tasks in which an observer mimics the behavior of a demonstrator. We examine whether rat hippocampal neurons may encode the behavior of a minirobot, but without requiring the animal to mimic it. Rather than finding social place cells, we observe that robot behavioral patterns modulate place fields coding animal position. This modulation may be confounded by correlations between robot movement and changes in the animal's position. Although rat position indeed significantly predicts robot behavior, we find that hippocampal ensembles code additional information about robot movement patterns. Fast-spiking interneurons are particularly informative about robot position and global behavior. In conclusion, when the animal's own behavior is conditional on external agents, the hippocampus multiplexes information about self and others.

Complementary Task Structure Representations in Hippocampus and Orbitofrontal Cortex during an Odor Sequence Task

Both hippocampus (HPC) and orbitofrontal cortex (OFC) have been shown to be critical for behavioral tasks that require use of an internal model or cognitive map, composed of the states and the relationships between them, which define the current environment or task at hand. One general idea is that the HPC provides the cognitive map, which is then transformed by OFC to emphasize information of relevance to current goals. Our previous analysis of ensemble activity in OFC in rats performing an odor sequence task revealed a rich representation of behaviorally relevant task structure, consistent with this proposal. Here, we compared those data to recordings from single units in area CA1 of the HPC of rats performing the same task. Contrary to expectations that HPC ensembles would represent detailed, even incidental, information defining the full task space, we found that HPC ensembles-like those in OFC-failed to distinguish states when it was not behaviorally necessary. However, hippocampal ensembles were better than those in OFC at distinguishing task states in which prospective memory was necessary for future performance. These results suggest that, in familiar environments, the HPC and OFC may play complementary roles, with the OFC maintaining the subjects' current position on the cognitive map or state space, supported by HPC when memory demands are high.

Neural Representation of Overlapping Path Segments and Reward Acquisitions in the Monkey Hippocampus

Disambiguation of overlapping events is thought to be the hallmark of episodic memory. Recent rodent studies have reported that when navigating overlapping path segments in the different routes place cell activity in the same overlapping path segments were remapped according to different goal locations in different routes. However, it is unknown how hippocampal neurons disambiguate reward delivery in overlapping path segments in different routes. In the present study, we recorded monkey hippocampal neurons during performance of three virtual navigation (VN) tasks in which a monkey alternately navigated two different routes that included overlapping path segments (common central hallway) and acquired rewards in the same locations in overlapping path segments by manipulating a joystick. The results indicated that out of 106 hippocampal neurons, 57 displayed place-related activity (place-related neurons), and 18 neurons showed route-dependent activity in the overlapping path segments, consistent with a hippocampal role in the disambiguation of overlapping path segments. Moreover, 75 neurons showed neural correlates to reward delivery (reward-related neurons), whereas 56 of these 75 reward-related neurons showed route-dependent reward-related activity in the overlapping path segments. The ensemble activity of reward-related neurons represented reward delivery, locations, and routes in the overlapping path segments. In addition, ensemble activity patterns of hippocampal neurons more distinctly represented overlapping path segments than non-overlapping path segments. The present results provide neurophysiological evidence of disambiguation in the monkey hippocampus, consistent with a hippocampal role in episodic memory, and support a recent computational model of "neural differentiation," in which overlapping items are better represented by repeated retrieval with competitive learning.

Neural Circuits Underlying Rodent Sociality: A Comparative Approach

All mammals begin life in social groups, but for some species, social relationships persist and develop throughout the course of an individual's life. Research in multiple rodent species provides evidence of relatively conserved circuitry underlying social behaviors and processes such as social recognition and memory, social reward, and social approach/avoidance. Species exhibiting different complex social behaviors and social systems (such as social monogamy or familiarity preferences) can be characterized in part by when and how they display specific social behaviors. Prairie and meadow voles are closely related species that exhibit similarly selective peer preferences but different mating systems, aiding direct comparison of the mechanisms underlying affiliative behavior. This chapter draws on research in voles as well as other rodents to explore the mechanisms involved in individual social behavior processes, as well as specific complex social patterns. Contrasts between vole species exemplify how the laboratory study of diverse species improves our understanding of the mechanisms underlying social behavior. We identify several additional rodent species whose interesting social structures and available ecological and behavioral field data make them good candidates for study. New techniques and integration across laboratory and field settings will provide exciting opportunities for future mechanistic work in non-model species.

Remembering rewarding futures: A simulation-selection model of the hippocampus

Despite tremendous progress, the neural circuit dynamics underlying hippocampal mnemonic processing remain poorly understood. We propose a new model for hippocampal function-the simulation-selection model-based on recent experimental findings and neuroecological considerations. Under this model, the mammalian hippocampus evolved to simulate and evaluate arbitrary navigation sequences. Specifically, we suggest that CA3 simulates unexperienced navigation sequences in addition to remembering experienced ones, and CA1 selects from among these CA3-generated sequences, reinforcing those that are likely to maximize reward during offline idling states. High-value sequences reinforced in CA1 may allow flexible navigation toward a potential rewarding location during subsequent navigation. We argue that the simulation-selection functions of the hippocampus have evolved in mammals mostly because of the unique navigational needs of land mammals. Our model may account for why the mammalian hippocampus has evolved not only to remember, but also to imagine episodes, and how this might be implemented in its neural circuits.

Abstract Representation of Prospective Reward in the Hippocampus

Motivation enhances memory by increasing hippocampal engagement during encoding. However, whether such increased hippocampal activation reflects encoding of the value of highly rewarding events per se is less understood. Here, using a monetary incentive encoding task with a novel manipulation, we tested in humans whether the hippocampus represents abstract reward value, independent of perceptual content. During functional MRI scanning, men and women studied object pairs, each preceded by a monetary reward cue indicating the amount of money they would receive if they successfully remembered the object pair at test. Reward cues varied on both the level of reward (penny, dime, and dollar) and visual form (picture or word) across trials to dissociate hippocampal responses to reward value from those reflecting the perceptual properties of the cues. Behaviorally, participants remembered pairs associated with the high reward (dollar) more often than pairs associated with lower rewards. Neural pattern-similarity analysis revealed that hippocampal and parahippocampal cortex activation patterns discriminated between cues of different value regardless of their visual form, and that hippocampal discrimination of value was most pronounced in participants who showed the greatest behavioral sensitivity to reward. Strikingly, hippocampal patterns were most distinct for reward cues that differed in value but had similar visual appearance, consistent with theoretical proposals of hippocampal-pattern differentiation of competing representations. Our data illustrate how contextual representations within the hippocampus go beyond space and time to include information about the motivational salience of events, with hippocampal reward coding tracking the motivational impact on later memory.SIGNIFICANCE STATEMENT Motivation, such as the promise of future rewards, enhances hippocampal engagement during encoding and promotes successful retention of events associated with valuable rewards. However, whether the hippocampus explicitly encodes reward value, dissociable from sensory information, is unclear. Here, we show that the hippocampus forms abstract representation of valuable rewards, encoding conceptual rather than perceptual information about the motivational context of individual events. Reward representation within the hippocampus is associated with preferential retention of high-value events in memory. Furthermore, we show that hippocampal-pattern differentiation serves to emphasize differences between visually similar events with distinct motivational salience. Collectively, these findings indicate that hippocampal contextual representations enable individuals to distinguish the motivational value of events, leading to prioritized encoding of significant memories.

The storage and recall of memories in the hippocampo-cortical system

A quantitative computational theory of the operation of the hippocampus as an episodic memory system is described. The CA3 system operates as a single attractor or autoassociation network (1) to enable rapid one-trial associations between any spatial location (place in rodents or spatial view in primates) and an object or reward and (2) to provide for completion of the whole memory during recall from any part. The theory is extended to associations between time and object or reward to implement temporal order memory, which is also important in episodic memory. The dentate gyrus performs pattern separation by competitive learning to create sparse representations producing, for example, neurons with place-like fields from entorhinal cortex grid cells. The dentate granule cells generate, by the very small number of mossy fibre connections to CA3, a randomizing pattern separation effect that is important during learning but not recall and that separates out the patterns represented by CA3 firing as being very different from each other. This is optimal for an unstructured episodic memory system in which each memory must be kept distinct from other memories. The direct perforant path input to CA3 is quantitatively appropriate for providing the cue for recall in CA3 but not for learning. The CA1 recodes information from CA3 to set up associatively learned backprojections to the neocortex to allow the subsequent retrieval of information to the neocortex, giving a quantitative account of the large number of hippocampo-neocortical and neocortical-neocortical backprojections. Tests of the theory including hippocampal subregion analyses and hippocampal NMDA receptor knockouts are described and support the theory.

Multivoxel Pattern Analysis Reveals 3D Place Information in the Human Hippocampus

The spatial world is three dimensional (3D) and humans and other animals move both horizontally and vertically within it. Extant neuroscientific studies have typically investigated spatial navigation on a horizontal 2D plane, leaving much unknown about how 3D spatial information is represented in the brain. Specifically, horizontal and vertical information may be encoded in the same or different neural structures with equal or unequal sensitivity. Here, we investigated these possibilities using fMRI while participants were passively moved within a 3D lattice structure as if riding a rollercoaster. Multivoxel pattern analysis was used to test for the existence of information relating to where and in which direction participants were heading in this virtual environment. Behaviorally, participants had similarly accurate memory for vertical and horizontal locations and the right anterior hippocampus (HC) expressed place information that was sensitive to changes along both horizontal and vertical axes. This is suggestive of isotropic 3D place encoding. In contrast, participants indicated their heading direction faster and more accurately when they were heading in a tilted-up or tilted-down direction. This direction information was expressed in the right retrosplenial cortex and posterior HC and was only sensitive to vertical pitch, which could reflect the importance of the vertical (gravity) axis as a reference frame. Overall, our findings extend previous knowledge of how we represent the spatial world and navigate within it by taking into account the important third dimension.

SIGNIFICANCE STATEMENT The spatial world is 3D. We can move horizontally across surfaces, but also vertically, going up slopes or stairs. Little is known about how the brain supports representations of 3D space. A key question is whether horizontal and vertical information is equally well represented. Here, we measured fMRI response patterns while participants moved within a virtual 3D environment and found that the anterior hippocampus (HC) expressed location information that was sensitive to the vertical and horizontal axes. In contrast, information about heading direction, found in retrosplenial cortex and posterior HC, favored the vertical axis, perhaps due to gravity effects. These findings provide new insights into how we represent our spatial 3D world and navigate within it.

The Interplay of Hippocampus and Ventromedial Prefrontal Cortex in Memory-Based Decision Making

Episodic memory and value-based decision making are two central and intensively studied research domains in cognitive neuroscience, but we are just beginning to understand how they interact to enable memory-based decisions. The two brain regions that have been associated with episodic memory and value-based decision making are the hippocampus and the ventromedial prefrontal cortex, respectively. In this review article, we first give an overview of these brain–behavior associations and then focus on the mechanisms of potential interactions between the hippocampus and ventromedial prefrontal cortex that have been proposed and tested in recent neuroimaging studies. Based on those possible interactions, we discuss several directions for future research on the neural and cognitive foundations of memory-based decision making.

Sublayer-Specific Coding Dynamics during Spatial Navigation and Learning in Hippocampal Area CA1

The mammalian hippocampus is critical for spatial information processing and episodic memory. Its primary output cells, CA1 pyramidal cells (CA1 PCs), vary in genetics, morphology, connectivity, and electrophysiological properties. It is therefore possible that distinct CA1 PC subpopulations encode different features of the environment and differentially contribute to learning. To test this hypothesis, we optically monitored activity in deep and superficial CA1 PCs segregated along the radial axis of the mouse hippocampus and assessed the relationship between sublayer dynamics and learning. Superficial place maps were more stable than deep during head-fixed exploration. Deep maps, however, were preferentially stabilized during goal-oriented learning, and representation of the reward zone by deep cells predicted task performance. These findings demonstrate that superficial CA1 PCs provide a more stable map of an environment, while their counterparts in the deep sublayer provide a more flexible representation that is shaped by learning about salient features in the environment. VIDEO ABSTRACT.

Place cells on a maze encode routes rather than destinations

Hippocampal place cells fire at different rates when a rodent runs through a given location on its way to different destinations. However, it is unclear whether such firing represents the animal’s intended destination or the execution of a specific trajectory. To distinguish between these possibilities, Lister Hooded rats (n = 8) were trained to navigate from a start box to three goal locations via four partially overlapping routes. Two of these led to the same goal location. Of the cells that fired on these two routes, 95.8% showed route-dependent firing (firing on only one route), whereas only two cells (4.2%) showed goal-dependent firing (firing similarly on both routes). In addition, route-dependent place cells over-represented the less discriminable routes, and place cells in general over-represented the start location. These results indicate that place cell firing on overlapping routes reflects the animal’s route, not its goals, and that this firing may aid spatial discrimination.

DOI:http://dx.doi.org/10.7554/eLife.15986.001

How does the brain represent the outside world? One way of answering this question is to study the brains of rats, because the basic plan of a rodent’s brain is similar to that of other mammals, such as humans. For example, the brains of rodents and humans both contain a structure called the hippocampus, which plays important roles in navigation and spatial memory. Cells within the hippocampus called place cells support these processes by firing electrical impulses whenever the animal occupies a specific location.

When a rat runs along a corridor in a maze, its place cells often fire as it approaches a choice point. A given place cell will typically fire before the rat chooses a path leading towards one particular location, but not before choices that lead to other locations. The firing that occurs prior to the choice point is termed “prospective firing”. However, it is not known whether the prospective firing of place cells represents the rat’s final destination, or the specific route the animal takes to get there.

To address this question, Grieves et al. designed a maze in which two different paths from a starting corridor led to the same goal location. If place cells represent the goal location, they should fire whichever route the rat chooses. However, if they represent the specific path the rat takes to the goal, they should fire on one or the other route, but not both.

Grieves et al. found that almost all place cells with prospective activity in the starting corridor fired on a single route, as opposed to firing on both routes to the common goal. This suggests that the prospective firing in the hippocampus reflects the route the animal will take, rather than its intended destination. A future challenge will be to understand how the way the hippocampus codes routes interacts with brain circuits that code for intended goals, and how the activity of these circuits influences the animal’s ability to navigate.

DOI:http://dx.doi.org/10.7554/eLife.15986.002

Effect of dentate gyrus disruption on remembering what happened where

Our previous studies using Bax knockout (Bax-KO) mice, in which newly generated granule cells continue to accumulate, disrupting neural circuitry specifically in the dentate gyrus (DG), suggest the involvement of the DG in binding the internally-generated spatial map with sensory information on external landmarks (spatial map-object association) in forming a distinct spatial context for each environment. In order to test whether the DG is also involved in binding the internal spatial map with sensory information on external events (spatial map-event association), we tested the behavior of Bax-KO mice in a delayed-non-match-to-place task. Performance of Bax-KO mice was indistinguishable from that of wild-type mice as long as there was no interruption during the delay period (tested up to 5 min), suggesting that on-line maintenance of working memory is intact in Bax-KO mice. However, Bax-KO mice showed profound performance deficits when they were removed from the maze during the delay period (interruption condition) with a sufficiently long (65 s) delay, suggesting that episodic memory was impaired in Bax-KO mice. Together with previous findings, these results suggest the role of the DG in binding spatial information derived from dead reckoning and nonspatial information, such as external objects and events, in the process of encoding episodic memory.

Prior fear conditioning and reward learning interact in fear and reward networks

The ability to flexibly adapt responses to changes in the environment is important for survival. Previous research in humans separately examined the mechanisms underlying acquisition and extinction of aversive and appetitive conditioned responses. It is yet unclear how aversive and appetitive learning interact on a neural level during counterconditioning in humans. This functional magnetic resonance imaging (fMRI) study investigated the interaction of fear conditioning and subsequent reward learning. In the first phase (fear acquisition), images predicted aversive electric shocks or no aversive outcome. In the second phase (counterconditioning), half of the CS+ and CS− were associated with monetary reward in the absence of electric stimulation. The third phase initiated reinstatement of fear through presentation of electric shocks, followed by CS presentation in the absence of shock or reward. Results indicate that participants were impaired at learning the reward contingencies for stimuli previously associated with shock. In the counterconditioning phase, prior fear association interacted with reward representation in the amygdala, where activation was decreased for rewarded compared to unrewarded CS− trials, while there was no reward-related difference in CS+ trials. In the reinstatement phase, an interaction of previous fear association and previous reward status was observed in a reward network consisting of substantia nigra/ventral tegmental area (SN/VTA), striatum and orbitofrontal cortex (OFC), where activation was increased by previous reward association only for CS− but not for CS+ trials. These findings suggest that during counterconditioning, prior fear conditioning interferes with reward learning, subsequently leading to lower activation of the reward network.

Limbic systems for emotion and for memory, but no single limbic system

The concept of a (single) limbic system is shown to be outmoded. Instead, anatomical, neurophysiological, functional neuroimaging, and neuropsychological evidence is described that anterior limbic and related structures including the orbitofrontal cortex and amygdala are involved in emotion, reward valuation, and reward-related decision-making (but not memory), with the value representations transmitted to the anterior cingulate cortex for action-outcome learning. In this 'emotion limbic system' a computational principle is that feedforward pattern association networks learn associations from visual, olfactory and auditory stimuli, to primary reinforcers such as taste, touch, and pain. In primates including humans this learning can be very rapid and rule-based, with the orbitofrontal cortex overshadowing the amygdala in this learning important for social and emotional behaviour. Complementary evidence is described showing that the hippocampus and limbic structures to which it is connected including the posterior cingulate cortex and the fornix-mammillary body-anterior thalamus-posterior cingulate circuit are involved in episodic or event memory, but not emotion. This 'hippocampal system' receives information from neocortical areas about spatial location, and objects, and can rapidly associate this information together by the different computational principle of autoassociation in the CA3 region of the hippocampus involving feedback. The system can later recall the whole of this information in the CA3 region from any component, a feedback process, and can recall the information back to neocortical areas, again a feedback (to neocortex) recall process. Emotion can enter this memory system from the orbitofrontal cortex etc., and be recalled back to the orbitofrontal cortex etc. during memory recall, but the emotional and hippocampal networks or 'limbic systems' operate by different computational principles, and operate independently of each other except insofar as an emotional state or reward value attribute may be part of an episodic memory.

Dopamine controls the neural dynamics of memory signals and retrieval accuracy

The human brain is capable of differentiating between new and already stored information rapidly to allow optimal behavior and decision-making. Although the neural mechanisms of novelty discrimination were often described as temporally constant (ie, with specific latencies), recent electrophysiological studies have demonstrated that the onset of neural novelty signals (ie, differences in event-related responses to new and old items) can be accelerated by reward motivation. While the precise physiological mechanisms underlying this acceleration remain unclear, the involvement of the neurotransmitter dopamine in both novelty and reward processing suggests that enhanced dopamine levels in the context of reward prospect may have a role. To investigate this hypothesis, we used magnetoencephalography (MEG) in combination with an old/new recognition memory task in which correct discrimination between old and new items was rewarded. Importantly, before the task, human subjects received either 150 mg of the dopamine precursor levodopa or placebo. For the placebo group, old/new signals peaked at ∼100 ms after stimulus onset over left temporal/occipital sensors. In contrast, after levodopa administration earliest old/new effects only emerged after ∼400 ms and retrieval accuracy was reduced as expressed in lower d' values. As such, our results point towards a previously unreported role of dopamine in controlling the chronometry of neural processes underlying the distinction between old and new information. They also suggest that this relationship follows a nonlinear function whereby slightly enhanced dopamine levels accelerate neural/cognitive processes and excessive dopamine levels impair them.

Distributed hippocampal patterns that discriminate reward context are associated with enhanced associative binding

Recent research indicates that reward-based motivation impacts medial temporal lobe (MTL) encoding processes, leading to enhanced memory for rewarded events. In particular, previous functional magnetic resonance imaging (fMRI) studies of motivated learning have shown that MTL activation is greater for highly rewarded events, with the degree of reward-related activation enhancement tracking the corresponding behavioral memory advantage. These studies, however, do not directly address leading theoretical perspectives that propose such reward-based enhancements in MTL encoding activation reflect enhanced discrimination of the motivational context of specific events. In this study, a high-value or low-value monetary cue preceded a pair of objects, indicating the future reward for successfully remembering the pair. Using representational similarity analysis and high-resolution fMRI, we show that MTL activation patterns are more similar for encoding trials preceded by the same versus different reward cues, indicating a distributed code in this region that distinguishes between motivational contexts. Moreover, we show that activation patterns in hippocampus and parahippocampal cortex (PHc) that differentiate reward conditions during anticipatory cues and object pairs relate to successful associative memory. Additionally, the degree to which patterns differentiate reward contexts in dentate gyrus/CA2,3 and PHc is related to individual differences in reward modulation of memory. Collectively, these findings suggest that distributed activation patterns in the human hippocampus and PHc reflect the rewards associated with individual events. Furthermore, we show that these activation patterns-which discriminate between reward conditions--may influence memory through the incorporation of information about motivational contexts into stored memory representations.

A quantitative theory of the functions of the hippocampal CA3 network in memory

A quantitative computational theory of the operation of the hippocampal CA3 system as an autoassociation or attractor network used in episodic memory system is described. In this theory, the CA3 system operates as a single attractor or autoassociation network to enable rapid, one-trial, associations between any spatial location (place in rodents, or spatial view in primates) and an object or reward, and to provide for completion of the whole memory during recall from any part. The theory is extended to associations between time and object or reward to implement temporal order memory, also important in episodic memory. The dentate gyrus (DG) performs pattern separation by competitive learning to produce sparse representations suitable for setting up new representations in CA3 during learning, producing for example neurons with place-like fields from entorhinal cortex grid cells. The dentate granule cells produce by the very small number of mossy fiber (MF) connections to CA3 a randomizing pattern separation effect important during learning but not recall that separates out the patterns represented by CA3 firing to be very different from each other, which is optimal for an unstructured episodic memory system in which each memory must be kept distinct from other memories. The direct perforant path (pp) input to CA3 is quantitatively appropriate to provide the cue for recall in CA3, but not for learning. Tests of the theory including hippocampal subregion analyses and hippocampal NMDA receptor knockouts are described, and support the theory.

Hippocampal neural correlates for values of experienced events

Newly experienced events are often remembered together with how rewarding the experiences are personally. Although the hippocampus is a candidate structure where subjective values are integrated with other elements of episodic memory, it is uncertain whether and how the hippocampus processes value-related information. We examined how activity of dorsal CA1 and dorsal subicular neurons in rats performing a dynamic foraging task was related to reward values that were estimated using a reinforcement learning model. CA1 neurons carried significant signals related to action values before the animal revealed its choice behaviorally, indicating that the information on the expected values of potential choice outcomes was available in CA1. Moreover, after the outcome of the animal's goal choice was revealed, CA1 neurons carried robust signals for the value of chosen action and they temporally overlapped with the signals related to the animal's goal choice and its outcome, indicating that all the signals necessary to evaluate the outcome of an experienced event converged in CA1. On the other hand, value-related signals were substantially weaker in the subiculum. These results suggest a major role of CA1 in adding values to experienced events during episodic memory encoding. Given that CA1 neuronal activity is modulated by diverse attributes of an experienced event, CA1 might be a place where all the elements of episodic memory are integrated.

Framing spatial cognition: neural representations of proximal and distal frames of reference and their roles in navigation

The most common behavioral test of hippocampus-dependent, spatial learning and memory is the Morris water task, and the most commonly studied behavioral correlate of hippocampal neurons is the spatial specificity of place cells. Despite decades of intensive research, it is not completely understood how animals solve the water task and how place cells generate their spatially specific firing fields. Based on early work, it has become the accepted wisdom in the general neuroscience community that distal spatial cues are the primary sources of information used by animals to solve the water task (and similar spatial tasks) and by place cells to generate their spatial specificity. More recent research, along with earlier studies that were overshadowed by the emphasis on distal cues, put this common view into question by demonstrating primary influences of local cues and local boundaries on spatial behavior and place-cell firing. This paper first reviews the historical underpinnings of the "standard" view from a behavioral perspective, and then reviews newer results demonstrating that an animal's behavior in such spatial tasks is more strongly controlled by a local-apparatus frame of reference than by distal landmarks. The paper then reviews similar findings from the literature on the neurophysiological correlates of place cells and other spatially correlated cells from related brain areas. A model is proposed by which distal cues primarily set the orientation of the animal's internal spatial coordinate system, via the head direction cell system, whereas local cues and apparatus boundaries primarily set the translation and scale of that coordinate system.

Excess folate during adolescence suppresses thyroid function with permanent deficits in motivation and spatial memory

Cognitive and memory deficits can be caused or exacerbated by dietary folate deficiency, which has been combatted by the addition of folate to grains and dietary supplements. The recommended dose of the B9 vitamin folate is 400 µg/day for adolescents and non-pregnant adults, and consumption above the recommended daily allowance is not considered to be detrimental. However, the effects of excess folate have not been tested in adolescence when neuro and endocrine development suggest possible vulnerability to long-term cognitive effects. We administered folate-supplemented (8.0 mg folic acid/kg diet) or control lab chow (2.7 mg folic acid/kg diet) to rats ad libitum from 30 to 60 days of age, and subsequently tested their motivation and learning and memory in the Morris water maze. We found that folate-supplemented animals had deficits in motivation and spatial memory, but they showed no changes of the learning- and memory-related molecules growth-associated protein-43 or Gs-α subunit protein in the hippocampus. They had decreased levels of thyroxine (T4) and triiodothyronine (T3) in the periphery and decreased protein levels of thyroid receptor-α1 and -α2 (TRα1 and TRα2) in the hippocampus. The latter may have been due to an observed increase of cytosine-phosphate-guanosine island methylation within the putative thyroid hormone receptor-α promoter, which we have mapped for the first time in the rat. Overall, folate supplementation in adolescence led to motivational and spatial memory deficits that may have been mediated by suppressed thyroid hormone function in the periphery and hippocampus.

Chemosensory learning in the cortex

Taste is a primary reinforcer. Olfactory–taste and visual–taste association learning takes place in the primate including human orbitofrontal cortex to build representations of flavor. Rapid reversal of this learning can occur using a rule-based learning system that can be reset when an expected taste or flavor reward is not obtained, that is by negative reward prediction error, to which a population of neurons in the orbitofrontal cortex responds. The representation in the orbitofrontal cortex but not the primary taste or olfactory cortex is of the reward value of the visual/olfactory/taste input as shown by devaluation experiments in which food is fed to satiety, and by correlations of the activations with subjective pleasantness ratings in humans. Sensory-specific satiety for taste, olfactory, visual, and oral somatosensory inputs produced by feeding a particular food to satiety is implemented it is proposed by medium-term synaptic adaptation in the orbitofrontal cortex. Cognitive factors, including word-level descriptions, modulate the representation of the reward value of food in the orbitofrontal cortex, and this effect is learned it is proposed by associative modification of top-down synapses onto neurons activated by bottom-up taste and olfactory inputs when both are active in the orbitofrontal cortex. A similar associative synaptic learning process is proposed to be part of the mechanism for the top-down attentional control to the reward value vs. the sensory properties such as intensity of taste and olfactory inputs in the orbitofrontal cortex, as part of a biased activation theory of selective attention.

Emerging, reemerging, and forgotten brain areas of the reward circuit: Notes from the 2010 Motivational Neural Networks conference

On April 24-27, 2010, the Motivational Neuronal Networks meeting took place in Wrightsville Beach, North Carolina. The conference was devoted to "Emerging, re-emerging, and forgotten brain areas" of the reward circuit. A central feature of the conference was four scholarly discussions of cutting-edge topics related to the conference's theme. These discussions form the basis of the present review, which summarizes areas of consensus and controversy, and serves as a roadmap for the next several years of research.

Contextual interaction between novelty and reward processing within the mesolimbic system

Medial temporal lobe (MTL) dependent long‐term memory for novel events is modulated by a circuitry that also responds to reward and includes the ventral striatum, dopaminergic midbrain, and medial orbitofrontal cortex (mOFC). This common neural network may reflect a functional link between novelty and reward whereby novelty motivates exploration in the search for rewards; a link also termed novelty “exploration bonus.” We used fMRI in a scene encoding paradigm to investigate the interaction between novelty and reward with a focus on neural signals akin to an exploration bonus. As expected, reward related long‐term memory for the scenes (after 24 hours) strongly correlated with activity of MTL, ventral striatum, and substantia nigra/ventral tegmental area (SN/VTA). Furthermore, the hippocampus showed a main effect of novelty, the striatum showed a main effect of reward, and the mOFC signalled both novelty and reward. An interaction between novelty and reward akin to an exploration bonus was found in the hippocampus. These data suggest that MTL novelty signals are interpreted in terms of their reward‐predicting properties in the mOFC, which biases striatal reward responses. The striatum together with the SN/VTA then regulates MTL‐dependent long‐term memory formation and contextual exploration bonus signals in the hippocampus. Hum Brain Mapp, 2011. © 2011 Wiley‐Liss, Inc.

A common mechanism for adaptive scaling of reward and novelty

Declarative memory is remarkably adaptive in the way it maintains sensitivity to relative novelty in both unknown and highly familiar environments. However, the neural mechanisms underlying this contextual adaptation are poorly understood. On the basis of emerging links between novelty processing and reinforcement learning mechanisms, we hypothesized that responses to novelty will be adaptively scaled according to expected contextual probabilities of new and familiar events, in the same way that responses to prediction errors for rewards are scaled according to their expected range. Using functional magnetic resonance imaging in humans, we show that the influence of novelty and reward on memory formation in an incidental memory task is adaptively scaled and furthermore that the BOLD signal in orbital prefrontal and medial temporal cortices exhibits concomitant scaled adaptive coding. These findings demonstrate a new mechanism for adjusting gain and sensitivity in declarative memory in accordance with contextual probabilities and expectancies of future events. Hum Brain Mapp, 2010. © 2010 Wiley‐Liss, Inc.

Hippocampal theta rhythm and drug-related reward-seeking behavior: an analysis of cocaine-induced conditioned place preference in rats

Drug cravings are elicited by environmental stimuli associated with the rewarding effects of drugs. As an animal model of such associative learning, conditioned place preference (CPP) is widely used. Since the hippocampus is closely related to reward memory and the hippocampal local field potential (LFP), and in particular the theta rhythm is known to be associated with bodily movements, the theta rhythm might be one of the key neural substrates. On the basis of this assumption, we recorded the behaviors and hippocampal LFP of eight rats during cocaine-induced acquisition and expression of CPP. The earliest appearance of phase-locked theta activity was observed before the rats entered the cocaine-paired environment after conditioning; after entrance, the theta disappeared. This phase-locked theta was stronger when the rats stayed for a long time in the cocaine-paired environment. Our observation suggested that the phase-locked hippocampal theta rhythm is related to the approaching behavior of the rat caused by reward memory. Thus, the role of the hippocampus in drug craving should be emphasized further.

A computational theory of episodic memory formation in the hippocampus

A quantitative computational theory of the operation of the hippocampus as an episodic memory system is described. The CA3 system operates as a single attractor or autoassociation network to enable rapid, one-trial associations between any spatial location (place in rodents or spatial view in primates) and an object or reward and to provide for completion of the whole memory during recall from any part. The theory is extended to associations between time and object or reward to implement temporal order memory, also important in episodic memory. The dentate gyrus performs pattern separation by competitive learning to produce sparse representations, producing for example neurons with place-like fields from entorhinal cortex grid cells. The dentate granule cells produce by the very small number of mossy fibre connections to CA3 a randomizing pattern separation effect important during learning but not recall that separates out the patterns represented by CA3 firing to be very different from each other, which is optimal for an unstructured episodic memory system in which each memory must be kept distinct from other memories. The direct perforant path input to CA3 is quantitatively appropriate to provide the cue for recall in CA3, but not for learning. The CA1 recodes information from CA3 to set up associatively learned backprojections to neocortex to allow subsequent retrieval of information to neocortex, providing a quantitative account of the large number of hippocampo-neocortical and neocortical-neocortical backprojections. Tests of the theory including hippocampal subregion analyses and hippocampal NMDA receptor knockouts are described and support the theory.

Rewarded outcomes enhance reactivation of experience in the hippocampus

Remembering experiences that lead to reward is essential for survival. The hippocampus is required for forming and storing memories of events and places, but the mechanisms that associate specific experiences with rewarding outcomes are not understood. Event memory storage is thought to depend on the reactivation of previous experiences during hippocampal sharp wave ripples (SWRs). We used a sequence switching task that allowed us to examine the interaction between SWRs and reward. We compared SWR activity after animals traversed spatial trajectories and either received or did not receive a reward. Here, we show that rat hippocampal CA3 principal cells are significantly more active during SWRs following receipt of reward. This SWR activity was further enhanced during learning and reactivated coherent elements of the paths associated with the reward location. This enhanced reactivation in response to reward could be a mechanism to bind rewarding outcomes to the experiences that precede them.

Tagging items in spatial working memory: a unit-recording study in the rat medial prefrontal cortex

The rat medial prefrontal cortex has been suggested to be involved in executive functions and, more specifically, in working memory and response selection. Here, we looked for prefrontal neural correlates as rats performed a modified radial arm maze task that taxed such functions. Rats had to learn the position of four rewarded arms among eight, and visit each rewarded arm only once, thus avoiding repeated visits. In addition, rats were left on the maze after the four successful visits to baited arms until they had visited all the arms twice. Prefrontal neural activity was examined during choice periods, i.e. 2s before the rat entered the arms. We found that a substantial proportion of recorded medial prefrontal neurons were selectively activated before either the first or second visit to the arms irrespective of their reward status, thereby tagging already visited arms. These behavioral correlates show that, within the rodent medial prefrontal cortex, neuronal populations demonstrate behavioral correlates suggestive of its role in guiding prospective search behavior and thus executive functions.

Correlates of reward-predictive value in learning-related hippocampal neural activity

Temporal difference learning (TD) is a popular algorithm in machine learning. Two learning signals that are derived from this algorithm, the predictive value and the prediction error, have been shown to explain changes in neural activity and behavior during learning across species. Here, the predictive value signal is used to explain the time course of learning-related changes in the activity of hippocampal neurons in monkeys performing an associative learning task. The TD algorithm serves as the centerpiece of a joint probability model for the learning-related neural activity and the behavioral responses recorded during the task. The neural component of the model consists of spiking neurons that compete and learn the reward-predictive value of task-relevant input signals. The predictive-value signaled by these neurons influences the behavioral response generated by a stochastic decision stage, which constitutes the behavioral component of the model. It is shown that the time course of the changes in neural activity and behavioral performance generated by the model exhibits key features of the experimental data. The results suggest that information about correct associations may be expressed in the hippocampus before it is detected in the behavior of a subject. In this way, the hippocampus may be among the earliest brain areas to express learning and drive the behavioral changes associated with learning. Correlates of reward-predictive value may be expressed in the hippocampus through rate remapping within spatial memory representations, they may represent reward-related aspects of a declarative or explicit relational memory representation of task contingencies, or they may correspond to reward-related components of episodic memory representations. These potential functions are discussed in connection with hippocampal cell assembly sequences and their reverse reactivation during the awake state. The results provide further support for the proposal that neural processes underlying learning may be implementing a temporal difference-like algorithm.

The hippocampus codes the uncertainty of cue-outcome associations: an intracranial electrophysiological study in humans

Learning to predict upcoming outcomes based on environmental cues is essential for adaptative behavior. In monkeys, midbrain dopaminergic neurons code two statistical properties of reward: a prediction error at the outcome and uncertainty during the delay period between cues and outcomes. Although the hippocampus is sensitive to reward processing, and hippocampal-midbrain functional interactions are well documented, it is unknown whether it also codes the statistical properties of reward information. To address this question, we recorded local field potentials from intracranial electrodes in human hippocampus while subjects learned to associate cues of slot machines with various monetary reward probabilities (P). We found that the amplitudes of negative event-related potentials covaried with uncertainty at the outcome, being maximal for P = 0.5 and minimal for P = 0 and P = 1, regardless of winning or not. These results show that the hippocampus computes an uncertainty signal that may constitute a fundamental mechanism underlying the role of this brain region in a number of functions, including attention-based learning, associative learning, probabilistic classification, and binding of stimulus elements.

Trial outcome and associative learning signals in the monkey hippocampus

In tasks of associative learning, animals establish new links between unrelated items by using information about trial outcome to strengthen correct/rewarded associations and modify incorrect/unrewarded ones. To study how hippocampal neurons convey information about reward and trial outcome during new associative learning, we recorded hippocampal neurons as monkeys learned novel object-place associations. A large population of hippocampal neurons (50%) signaled trial outcome by differentiating between correct and error trials during the period after the behavioral response. About half these cells increased their activity following correct trials (correct up cells) while the remaining half fired more following error trials (error up cells). Moreover, correct up cells, but not error up cells, conveyed information about learning by increasing their stimulus-selective response properties with behavioral learning. These findings suggest that information about successful trial outcome conveyed by correct up cells may influence new associative learning through changes in the cell's stimulus-selective response properties.

Integration of gravitational torques in cerebellar pathways allows for the dynamic inverse computation of vertical pointing movements of a robot arm

BACKGROUND

Several authors suggested that gravitational forces are centrally represented in the brain for planning, control and sensorimotor predictions of movements. Furthermore, some studies proposed that the cerebellum computes the inverse dynamics (internal inverse model) whereas others suggested that it computes sensorimotor predictions (internal forward model).

METHODOLOGY/PRINCIPAL FINDINGS

This study proposes a model of cerebellar pathways deduced from both biological and physical constraints. The model learns the dynamic inverse computation of the effect of gravitational torques from its sensorimotor predictions without calculating an explicit inverse computation. By using supervised learning, this model learns to control an anthropomorphic robot arm actuated by two antagonists McKibben artificial muscles. This was achieved by using internal parallel feedback loops containing neural networks which anticipate the sensorimotor consequences of the neural commands. The artificial neural networks architecture was similar to the large-scale connectivity of the cerebellar cortex. Movements in the sagittal plane were performed during three sessions combining different initial positions, amplitudes and directions of movements to vary the effects of the gravitational torques applied to the robotic arm. The results show that this model acquired an internal representation of the gravitational effects during vertical arm pointing movements.

CONCLUSIONS/SIGNIFICANCE

This is consistent with the proposal that the cerebellar cortex contains an internal representation of gravitational torques which is encoded through a learning process. Furthermore, this model suggests that the cerebellum performs the inverse dynamics computation based on sensorimotor predictions. This highlights the importance of sensorimotor predictions of gravitational torques acting on upper limb movements performed in the gravitational field.

Personality traits are differentially associated with patterns of reward and novelty processing in the human substantia nigra/ventral tegmental area

BACKGROUND

The long-standing observation that the novelty-seeking personality trait is a predictor of drug use and other reinforcable risky behaviors raises the question as to how novelty and reward processing functionally interact in mesolimbic dopaminergic circuitry and how this interaction is modulated by the novelty-seeking personality trait.

METHODS

Functional magnetic resonance imaging (fMRI) hemodynamic responses to novelty and reward (monetary incentive) from the substantia nigra/ventral tegmental area (SN/VTA), the nucleus accumbens (NAcc), and the hippocampus of 29 subjects were correlated with novelty-seeking scores. These correlations were compared with those obtained for scores of reward-dependence. The fMRI data were taken from two experiments in which the interaction of novelty and reward was manipulated as a within-subject variable, and long-term memory for the critical stimuli was assessed after 24 hours.

RESULTS

Novelty-seeking was positively correlated with SN/VTA activation elicited by novel cues that did not predict reward, whereas reward-dependence was related to activations elicited by novel cues that predicted reward. The positive correlation between SN/VTA responses to novelty and novelty-seeking scores was accompanied by a negative correlation with reward-related SN/VTA activation and memory enhancement.

CONCLUSIONS

SN/VTA responses to novelty and reward are differentially affected by personality traits of novelty-seeking and reward-dependence. Importantly, novelty-seekers were more responsive to novel cues in the absence of reward and needed less reward to boost their memory for novel cues. These observations strongly suggest that for novelty-seekers, the motivational value of novelty is not necessarily based on actual reward-predicting stimulus properties.

Lesion of the ventral and intermediate hippocampus abolishes anticipatory activity in the medial prefrontal cortex of the rat

The medial prefrontal cortex (mPFC) of the rat receives a prominent input from the ventral two thirds of the hippocampus, a structure important for spatial awareness, working memory and motivation. We recently found [Hok V, Lenck-Santini PP, Roux S, Save E, Muller RU, Poucet B. Goal-related activity in hippocampal place cells. J Neurosci 2007;27:472-82.] that neurones in the dorsal hippocampus exhibit anticipatory firing prior to the release of a food pellet on an operant task. Here we look for similar activity in the mPFC on the same task and test whether this activity is dependent on the hippocampus. Rats were trained to navigate to a goal zone, wait for the release of a food pellet and then forage for the pellet while unit activity was recorded in the prelimbic and infralimbic areas of the mPFC. Two 16 min sessions were conducted per day, one session with the goal delimited by a cue disc, the second without the cue. In controls, a large proportion of mPFC neurones exhibited activity similar to that seen in the hippocampus while the animal was stationary at the goal. Over half exhibited the same activity regardless of goal location. Anticipatory activity was largely abolished in animals with bilateral lesions of the ventral and intermediate hippocampus, both in cued and uncued sessions. Even though lesioned animals continued to perform the task, they tended to leave the goal zone prematurely. We suggest that the anticipatory activity in the mPFC is dependent on similar activity in the hippocampus and that both structures have a role in either impulse control or reward expectation.