The authors draw together the results of a series of detailed computational studies and show how they are contributing to the development of a theory of hippocampal function. A new part of the theory introduced here is a quantitative analysis of how backprojections from the hippocampus to the neocortex could lead to the recall of recent memories. The theory is then compared with other theories of hippocampal function. First, what is computed by the hippocampus is considered. The hypothesis the authors advocate, on the basis of the effects of damage to the hippocampus and neuronal activity recorded in it, is that it is involved in the formation of new memories by acting as an intermediate-term buffer store for information about episodes, particularly for spatial, but probably also for some nonspatial, information. The authors analyze how the hippocampus could perform this function, by producing a computational theory of how it operates, based on neuroanatomical and neurophysiological information about the different neuronal systems con-tained within the hippocampus. Key hypotheses are that the CA3 pyramidal cells operate as a single autoassociation network to store new episodic information as it arrives via a number of specialized preprocessing stages from many association areas of the cerebral cortex, and that the dentate

this paper. The cortex on the orbital surface of the frontal lobe includes area 13 caudally and area 14 medially, and the cortex on the inferior convexity includes area 12 caudally and area 11 anteriorly (Fig. 1) (Carmichael and Price, 1994; Petrides and Pandya, 1994; Price et al., 1996). This brain region is well developed in primates, including humans, but poorly developed in rodents, with homologies to areas found in primates uncertain, so that care must be used in interpretation of the term `orbitofrontal ' when applied to rodents (Uylings and van Eden, 1990). To understand the function of this brain region in humans, the majority of the studies described were therefore performed with macaques or with humans

ygdala was activated (region of interest analysis, P , 0.025 corrected) by the pleasant taste of glucose (5/7 subjects) as well as by the aversive taste of salt (4/7 subjects). Activation by both stimuli was also found in the frontal opercular/ insular (primary) taste cortex. We conclude that the orbitofrontal cortex is involved in processing tastes that have both positive and negative affective valence and that different areas of the orbitofrontal cortex may be activated by pleasant and unpleasant tastes. We also conclude that the amygdala is activated not only by an affectively unpleasant taste, but also by a taste that is affectively pleasant, thus providing evidence that the amygdala is involved in effects produced by positively affective as well as by negatively affective stimuli. INTRODUCTION The aims of this study are to investigate the representation of taste in the human brain and in particular to compare and contrast the representatio

Abstract—To investigate the role of the primate amygdala in stimulus-reinforcement association learning, the activity of single amygdala neurons was recorded in macaques during two memory tasks. In a visual discrimination task, a population of neurons (17/659) was analyzed which responded differentially to a visual stimulus which always indicated that the primary reinforcer fruit juice could be obtain if the monkey licked, and a different visual stimulus that indicated that the primary reinforcer aversive saline would be obtained if the monkey licked. Most (16/17) of these neurons responded more to the reward-related than the aversive visual stimulus. In a recognition memory task, the majority (12/14 analyzed) of these neurons responded equally well to the trial unique stimuli when they were shown as novel and the monkey had to not lick in order to avoid saline, and when they were shown

Abstract—The primate amygdala is implicated in the control of behavioral responses to foods and in stimulus-reinforcement learning, but only its taste representation of oral stimuli has been investigated previously. Of 1416 macaque amygdala neurons recorded, 44 (3.1%) responded to oral stimuli. Of the 44 orally responsive neurons, 17 (39%) represent the viscosity of oral stimuli, tested using carboxymethyl-cellulose in the range 1–10,000 cP. Two neurons (5%) responded to fat in the mouth by encoding its texture (shown by the responses of these neurons to a range of fats, and also to non-fat oils such as silicone oil ((Si(CH 3) 2O) n) and mineral oil (pure hydrocarbon), but no or small responses to the cellulose viscosity series or to the fatty acids linoleic acid and lauric acid). Of the 44 neurons, three (7%) responded to gritty texture (produced by microspheres suspended in cellulose). Eighteen neurons (41%) responded to the temperature of liquid in the mouth. Some amygdala neurons responded to capsaicin, and some to fatty acids (but not to fats in the mouth). Some amygdala neurons respond to taste, texture and temperature unimodally, but others combine these inputs. These results provide fundamental evidence about the information channels used to represent the texture and flavor of food in a part of the brain important in appetitive responses to food and in learning associations to reinforcing oral stimuli, and are relevant to understanding the physiological and pathophysiological processes related to food intake, food selection, and the effects of variety of food texture in combination with taste and other inputs on food intake. © 2005 Published by Elsevier Ltd on behalf of IBRO. Key words: appetitive learning, Pavlovian conditioning, obesity, food intake, reward. The amygdala is implicated in emotion and motivation by lesion, single neuron recording, and neuroimaging investigations (Sanghera et al., 1979; Nishijo et al., 1988a; Davis,

The primate anterior hippocampus (which corresponds to the rodent ventral hippocampus) receives inputs from brain regions involved in reward processing, such as the amygdala and orbitofrontal cortex. To investigate how this affective input may be incorporated into primate hippocampal function, we recorded neuronal activity while rhesus macaques performed a reward–place association task in which each spatial scene shown on a video monitor had one location that, if touched, yielded a preferred fruit juice reward and a second location that yielded a less-preferred juice reward. Each scene had different locations for the different rewards. Of 312 neurons analyzed in the hippocampus, 18 % responded more to the location of the preferred reward in different scenes, and 5 % responded to the location of theless-preferredreward.Whenthelocationsofthepreferredrewardsinthesceneswerereversed,60%of44hippocampalneuronstested reversedthelocationtowhichtheyresponded,showingthatthereward–placeassociationscouldbealteredbynewlearninginafewtrials. The majority (82%) of these 44 hippocampal neurons tested did not respond to reward associations in a visual discrimination, object– reward association task. Thus, the primate hippocampus contains a representation of the reward associations of places “out there ” being viewed. By associating places with the rewards available, the concept that the primate hippocampus is involved in object–place event memory is now extended to remembering goals available at different spatial locations. This is an important type of association memory. Key words: hippocampus; episodic memory; macaque; spatial view cells; place cells; reward; associative learning