Responses of neurons in the inferior temporal cortex in short term and serial recognition memory tasks

Gaffan and Weiskrantz (1980) and Mishkin (1982) have shown that lesions to the inferior temporal visual cortex can impair the performance of serial visual recognition memory tasks. In order to provide evidence on whether the inferior temporal visual cortex contains a mechanism which enables memory to span the intervening items in a serial recognition task, or whether the inferior temporal cortex is merely afferent to such recent memory mechanisms, we analysed the activity of single neurons in the inferior temporal visual cortex and the adjacent cortex in the superior temporal sulcus in both delayed match to sample and serial recognition memory tasks. In the serial recognition task, various numbers of stimuli intervened between the first and second presentations of a stimulus. A considerable proportion (64/264 or 26%) of visually responsive inferotemporal neurons showed a different response to the "novel" and "familiar" presentations of a stimulus in the serial recognition memory task, and often a corresponding difference in response between the sample and match presentations of a stimulus in the delayed match to sample task. For the majority of neurons this difference was not sustained across even one intervening stimulus in the serial recognition task, and no neurons bridged more than 2 intervening stimuli. These results show that neurons in the inferior temporal cortex have responses which would be useful for a short term visual memory for stimuli, but would not be useful in recency memory tasks in which more than one stimulus intervenes between the first and second presentations of a stimulus. In this investigation, neurons were recorded both in the cortex on the inferior temporal gyrus (commonly called inferior temporal visual cortex, and consisting of areas TE3, TE2 and TE1 of Seltzer and Pandya 1978), and in the cortex in the adjacent anterior part of the superior temporal sulcus, in which a number of different temporal cortical visual areas have now been described.