Topographic patterns of spike propagation in the primate prefrontal cortex

Wael F. Asaad and Earl K. Miller

Center for Learning & Memory
RIKEN-MIT Neuroscience Research Center
Dept. of Brain & Cognitive Science
Massachusetts Institute of Technology

Using a multi-electrode array to record simultaneously across several broadly-spaced sites in the monkey lateral prefrontal cortex during three working memory tasks, we characterized the temporal relationships of neuronal activity across relatively wide regions of cortex (two to nine millimeters). We found that temporal correlations at ranges up to about five millimeters were generally positive, but between five and seven millimeters were generally negative. Temporal interactions were rarely observed beyond seven millimeters. Interestingly, when we examined the polarity of each correlated pair, we found that spikes from many different pairs tended to propagate in a coherent direction across the neocortex. Furthermore, this pattern was dependent upon the phase of the behavioral task being performed. These results suggest that the smooth "flow" of spiking activity across the cortex might provide a substrate for its graded transformation between adjacent cortical regions and does not support the notion that the neocortex consists of distinct, or modular processing subunits.