Formation of cell assemblies in the prefrontal cortex of macaque monkeys during a distance and a temporal discrimination task

Neurons synchronize their activity organizing into larger groups called cell assemblies. We studied the formation of cell assemblies in the macaque prefrontal cortex during the execution of two tasks involving duration and distance discriminations. Using a recent algorithm for cell assembly detection, we extracted the spikes fired during the assembly activation (assembly-spikes) from the overall activities (all-spikes) and we calculated their optimal bins and lags. Focusing on assembly of two cells, we found that the formation of such assemblies occurred more frequently for close neurons (neurons recorded by the same electrode) than for farther ones. We found also that their synchronization occurred without any lag more often for close than for far neurons. Therefore, distant neurons appear to have activities that correlate more sequentially. Furthermore, we observed that these assemblies of neighboring neurons persisted more often between tasks suggesting that the assemblies formed by neighboring neurons were more multipurpose. Finally, we focused on the spatial preferences for the right and the left responses. We found that while the probability that both neurons shared the same preference was close to chance considering the all-spikes, it increased to 80% by considering only the assembly-spikes. Our results suggest that this method of analysis has great potential for getting an insight into how neurons of the assembly orchestrate during task execution.