INVESTIGATION OF LONG-TERM RECOGNITION AND ASSOCIATION MEMORY IN UNITRESPONSES FROM INFEROTEMPORAL CORTEX

We investigated recognition and association memory in the responses of single units isolated in the inferior temporal cortex of a macaque wh ile it performed a visual discrimination task. The unit responses show ed significant recognition memory (a decreased response upon image rep etition). Furthermore, a recognition memory appeared to be a permanent feature in these units. Such memory was evident in responses recorded at least 1 h after the most recent presentations of the more familiar images and may have been built up over the months of training. For th ese cells, the shorter-term recognition memory (seconds) and the longe r-term recognition memory (hour plus) were significantly correlated (0 .68). In these same cells associative memory was investigated with ten abstract images which had been randomly and permanently paired. The m onkey had been taught to discriminate these five pairs from other simi lar pairs of images. Neither the spike count nor temporal response sha pe (as determined by a principal-components analysis) showed increased similarity for the images that had been paired. The cells that had bo th short-term and long-term recognition memory had responses to previo usly paired stimuli that were no more similar than expected by chance.