The Journal of Neuroscience, May 15, 2001, 21(10):3646-3655
Coding Specificity in Cortical Microcircuits: A
Multiple-Electrode Analysis of Primate Prefrontal Cortex
Christos
Constantinidis,
Matthew N.
Franowicz, and
Patricia S.
Goldman-Rakic
Section of Neurobiology, Yale School of Medicine, New Haven,
Connecticut 06510
Neurons with directional specificities are active in the prefrontal
cortex (PFC) during tasks that require spatial working memory. Although
the coordination of neuronal activity in PFC is thought to be
maintained by a network of recurrent connections, direct physiological
evidence regarding such networks is sparse. To gain insight into the
functional organization of the working memory system in
vivo, we recorded simultaneously from multiple neurons spaced
0.2-1 mm apart in monkeys performing an oculomotor delayed response
task. We used cross-correlation analysis and characterized the
effective connectivity between neurons in relation to their spatial and
temporal response properties. The majority of narrow (<5 msec)
cross-correlation peaks indicated common input and were most often
observed between pairs of neurons within 0.3 mm of each other. Neurons
recorded at these distances represented the full range of spatial
locations, suggesting that the entire visual hemifield is represented
in modules of corresponding dimensions. Nearby neurons could be
activated in any epoch of the behavioral task (stimulus presentation,
delay, response). The incidence and strength of cross-correlation,
however, was highest among cells sharing similar spatial tuning and
similar temporal profiles of activation across task epochs. The
dependence of correlated discharge on the functional properties of
neurons was observed both when we analyzed firing from the task period
as well as from baseline fixation. Our results suggest that the coding
specificity of individual neurons extends to the local circuits of
which they are part.
Key words:
working memory; prefrontal cortex; primate; cross-correlation; saccade; learning and memory
Copyright © 2001 Society for Neuroscience 0270-6474/01/21103646-10$05.00/0