Stimulus-dependent augmented gamma oscillatory activity between the functionally connected cortical neurons in the primary visual cortex

Neuronal assemblies typically synchronise within the gamma oscillatory band (30-80Hz) and are fundamental to information processing. Despite numerous investigations, the exact mechanisms and origins of gamma oscillations are yet to be known. Here, through multiunit recordings in the primary visual cortex of cats, we show that the strength of gamma power (20-40 and 60-80Hz) is significantly stronger between the functionally connected units than between the unconnected units within an assembly. Furthermore, there is increased frequency coherence in the gamma band between the connected units than between the unconnected units. Finally, the higher gamma rhythms (60-80Hz) are mostly linked to the fast-spiking neurons. These results led us to postulate that gamma oscillations are intrinsically generated between the connected units within cell assemblies (microcircuits) in relation to the stimulus within an emergent 50-ms temporal window of opportunity'.