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Abstract

Previous analysis of LFPs recorded from the macaque inferior convexity of the Prefrontal Cortex with Utah arrays revealed a dominant travelling wave in the beta band propagating along the ventral-dorsal plane [1, 2]. We hypothesized that propagating rhythmic activity reflects the intrinsic dynamics of the underlying neural populations which might be instrumental to information processing functions such as sensory integration. Here, we investigated the relationship between multi-unit spiking activities and LFPs in the same area of the Prefrontal Cortex. We computed spike-field coherence for each channel of the array. The results showed that many recording sites exhibited a distinctive peak in the beta frequency range both for spontaneous activity and during visual stimulation (A). Then we computed the beta band phase locking of spikes for each channel to a common LFP reference channel. The results showed that many recording sites exhibited locking of spikes to the same phase of remote beta band LFP (B). This result was observed for many LFP reference channels, suggesting spikes in all channels are synchronized to a common phenomenon. To characterize this phenomenon, we developed a new methodology inspired by spike triggered analysis to capture the dominant underlying spatio-temporal pattern of beta oscillations associated to spiking activity. The dominant spatio-temporal pattern estimated by matrix factorization, exhibits a phase gradient along the ventral-dorsal plane (C), suggesting that multi-unit activities across the array are synchronized to the global travelling wave previously observed along this direction in the LFP signal. Our result suggests spikes are synchronized to large scale travelling wave in the beta band. We postulate this reflects an endogenous mechanism for the large scale coordination of population activity. Further information theoretic analysis will address how this mechanism serves distributed sensory encoding and processing in this area.