Reward is important for shaping goal-directed behaviour. After stimulus-reward associative learning, an organism can assess the motivational value of the incoming stimuli on the basis of past experience (retrospective processing), and predict forthcoming rewarding events (prospective processing). The traditional role of the sensory thalamus is to relay current sensory information to cortex. Here we find that non-primary thalamic neurons respond to reward-related events in two ways. The early, phasic responses occurred shortly after the onset of the stimuli and depended on the sensory modality. Their magnitudes resisted extinction and correlated with the learning experience. The late responses gradually increased during the cue and delay periods, and peaked just before delivery of the reward. These responses were independent of sensory modality and were modulated by the value and timing of the reward. These observations provide new evidence that single thalamic neurons can code for the acquired significance of sensory stimuli in the early responses (retrospective coding) and predict upcoming reward value in the late responses (prospective coding).

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Eifuku, Satoshi, Wania C. De Souza, Ryoi Tamura, Hisao Nishijo, and Taketoshi Ono. Neuronal correlates of face identification in the monkey anterior temporal cortical areas. J Neurophysiol 91: 358 -371, 2004; 10.1152/jn.00198.2003. To investigate the neuronal basis underlying face identification, the activity of face neurons in the anterior superior temporal sulcus (STS) and the anterior inferior temporal gyrus (ITG) of macaque monkeys was analyzed during their performance of a face-identification task. The face space was composed by the activities of face neurons during the face-identification task, based on a multidimensional scaling (MDS) method; the face space composed by the anterior STS neurons represented facial views, whereas that composed by the anterior ITG neurons represented facial identity. The temporal correlation between the behavioral reaction time of the animal and the latency of face-related neuronal responses was also analyzed. The response latency of some of the face neurons in the anterior ITG exhibited a significant correlation with the behavioral reaction time, whereas this correlation was not significant in the anterior STS. The correlation of the latency of face-related neuronal responses in the anterior ITG with the behavioral reaction time was not found to be attributed to the correlation between the response latency and the magnitude of the neuronal responses. The present results suggest that the anterior ITG is closely related to judgments of facial identity, and that the anterior STS is closely related to analyses of incoming perceptual information; face identification in monkeys might involve interactions between the two areas. I N T R O D U C T I O NThe identification of faces is a distinctive cognitive ability of primates and it plays an important role in social communication Bruce and Young 1998). Face neurons that respond selectively to the sight of faces were first identified in a region of the anterior temporal cortex in monkeys in the 1980s (Bruce et al. 1981;Perrett et al. 1982); such neurons have subsequently been identified in various areas of the monkey brain (Desimone et al. 1984;Harries and Perrett 1992;Hasselmo et al. 1989;Nakamura et al. 1992;Perrett et al. 1985;Scalaidhe et al. 1997;Yamane et al. 1988). In these previous studies, neuronal activity in response to faces was recorded in anesthetized immobilized monkeys or in alert monkeys that performed passive viewing or face-discrimination tasks. Some studies reported the existence of face neurons that might encode facial identity Sugase et al. 1999). However, it remains unclear how face neurons are related to the process of face identification; to determine this relationship in an animal model, we would need to have the animals perform face-identification tasks.Functional imaging (Halgren et al. 1999;Haxby et al. 1999;Hoffman and Haxby 2000;Ishai et al. 1999;Kanwisher et al. 1997) and evoked potential studies McCarthy et al. 1997McCarthy et al. , 1999Puce et al. 1999) of human brains revealed that multiple regions ...

Neuropsychological data in humans demonstrated a pivotal role of the medial temporal lobe, including the hippocampal formation (HF) and the parahippocampal gyrus (PH), in allocentric (environment-centered) spatial learning and memory. In the present study, the functional significance of the monkey HF and PH neurons in allocentric spatial processing was analyzed during performance of the spatial tasks. In the tasks, the monkey either freely moved to one of four reward areas in the experimental field by driving a cab that the monkey rode (real translocation task) or freely moved a pointer to one of four reward areas on the monitor (virtual translocation task) by manipulating a joystick. Of 389 neurons recorded from the monkey HF and PH, 166 had place fields that displayed increased activity in a specific area in the experimental field and/or on the monitor (location-differential neurons). More HF and PH neurons responded in the real translocation task. These neurons had low mean spontaneous firing rates (0.96 spikes/sec), similar to those of rodent HF place cells. The remaining nonresponsive neurons had significantly higher mean firing rates (8.39 spikes/ sec), similar to interneurons or cells in the rodent HF. Furthermore, most location-differential neurons showed different responses in different tasks. These results suggest that the HF and PH are crucial in allocentric information processing and, moreover, that the HF can encode different reference frames that are context or task-dependent. This may be the neural basis of episodic memory.

The amygdala (AM) receives information from various sensory modalities via the neocortex and directly from the thalamus and brain stem and plays an important role in ingestive behaviors. In the present study, neuronal activity was recorded in the AM and amygdalostriatal transition area of rats during discrimination of conditioned sensory stimuli and ingestion of sapid solutions. Of the 420 responsive neurons, 227 responded exclusively to one sensory modality, 120 responded to two or more modalities, and the remaining 73 could not be classified. Among the responsive neurons, 108 responded to oral-sensory stimulation (oral-sensory neurons). In detailed analyses of 84 of these oral-sensory neurons, 24 were classified as taste responsive and were located mainly in the central nucleus of the AM. The other 60 oral-sensory neurons were classified as nontaste oral-sensory neurons and were distributed widely throughout the AM. Both the taste and nontaste oral-sensory neurons also responded to other sensory stimuli. Of the 24 taste neurons, 21 were tested at least with four standard taste solutions. On the basis of the magnitudes of their responses to these sapid stimuli, the taste neurons were classified as follows: seven sucrose-best, four NaCl-best, three citric acid-best, and six quinine HCl-best. The remaining cell responded significantly only to lysine HCl and monosodium glutamate. Multivariate analyses of these 21 taste neurons suggested that, in the AM, taste quality was processed based on palatability. Taken with previous lesion studies, the present results suggest that the AM plays a role in the evaluation of taste palatability and in the association of taste stimuli with other sensory stimuli.