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Abstract:
Single neurons in the inferotemporal visual cortex of monkeys are known to modulate their activity in response to highly specific patterns, including complex shapes, objects, and faces. While numerous single-unit studies have explored feature selectivity and temporal patterning of responses in these areas, traditional recording techniques have provided only indirect information regarding their long-term stability. Here we address this issue using chronic implanted microelectrodes, which allowed us to monitor the activity of individual visually responsive neurons over periods of days and weeks. Each monkey was implanted with a thin bundle of 64 microwires (for one monkey in the anterior inferotemporal cortex (AIT), for the other in the superior temporal sulcus (STS)), and trained to view a small fixation point for several seconds while a stimulus was presented. The stimuli consisted of a diverse set of images that the monkey had seen many times prior to the recordings, including faces, animals, objects, and geometrical patterns. Activity was recorded over a period of approximately one year in one animal and 4 months in the other. Individual neurons were found to be highly stimulus-selective in the temporal profiles of their responses, showing robust differences in latency, transience, and amplitude. We recorded for several consecutive days from 55 isolated neurons, 10 of which were monitored for a week or more. We found that the fine temporal patterning for different stimuli was remarkably consistent during this period. While previous physiological experiments have demonstrated that representations in the inferotemporal areas can be shaped by experience and learning, the present findings demonstrate that the specific role of individual neurons in the analysis of complex patterns is not under a state of continual reorganization.
