We recorded the activity of single neurons in the primary visual cortex, the first cortical stage of visual processing, and inferior temporal cortex, the last cortical stage, to study the mechanisms underlying visual perception. When neurons were analyzed as communication channels carrying information in their responses, the response patterns seen could only be represented as the sum of several (3-6) simultaneous, independent patterns of activity. These activity patterns were analyzed as temporal code, and this code was found to contain more information than that conveyed by the response strength, the usual measure of neuronal response. The proportion of information carried in the temporal code increases steadily as one proceeds from the periphery through progressively more and more central statious of the visual system. Neurons recorded from inferior temporal cortex while monkeys perform a simple visual memory task, matching-to- sample, carry information differentiating the physical dimensions of the stimuli as well as their meaning, i.e., their whether each is the sample, the matching, or the nonmatching stimulus. Each member of a neuronal pair recorded simultaneously from a single electrode in both primary and inferior temporal cortex is independent of the other member, i.e., their information adds. This suggests that local processing is carried out by combining independent neuronal analyses of the stimulus being viewed.

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National Institute of Mental Health (NIMH)
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Nakahara, Hiroyuki; Amari, Shun-ichi; Richmond, Barry J (2006) A comparison of descriptive models of a single spike train by information-geometric measure. Neural Comput 18:545-68
Shidara, Munetaka; Richmond, Barry J (2005) Effect of visual noise on pattern recognition. Exp Brain Res 163:239-41
Richmond, Barry; Wiener, Matthew (2004) Recruitment order: a powerful neural ensemble code. Nat Neurosci 7:97-8
Wiener, Matthew C; Richmond, Barry J (2003) Decoding spike trains instant by instant using order statistics and the mixture-of-Poissons model. J Neurosci 23:2394-406
Wiener, Matthew C; Richmond, Barry J (2002) Model based decoding of spike trains. Biosystems 67:295-300
Shidara, Munetaka; Richmond, Barry J (2002) Anterior cingulate: single neuronal signals related to degree of reward expectancy. Science 296:1709-11
Richmond, B (2001) Neuroscience. Information coding. Science 294:2493-4
Wiener, M C; Oram, M W; Liu, Z et al. (2001) Consistency of encoding in monkey visual cortex. J Neurosci 21:8210-21
Oram, M W; Hatsopoulos, N G; Richmond, B J et al. (2001) Excess synchrony in motor cortical neurons provides redundant direction information with that from coarse temporal measures. J Neurophysiol 86:1700-16
Liu, Z; Murray, E A; Richmond, B J (2000) Learning motivational significance of visual cues for reward schedules requires rhinal cortex. Nat Neurosci 3:1307-15

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