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Abstract:
Previous studies using voltage sensitive dyes imaging (VSDI) carried out on anesthetized cats reported that spontaneous ongoing cortical activity in the primary visual cortex represents dynamics spatial patterns, many of which resembling the functional architecture of orientation domains, and span large cortical areas (Grinvald et al., 1989; Arieli et al., 1995; Arieli et al., 1996; Tsodyks et al., 1999; Kenet et al., 2003; also Fox et al., 2006; Fox et al., 2007b). Those results suggest that ongoing coherent activity may play an important role in cortical processing and high cognitive functions, as well as challenge the classical notion which considers spontaneous (ongoing) cortical activity as noise (Ferster D., 1996; Ringach D.L., 2003; Fox et al., 2007a).
We preformed VSDI of ongoing cortical activity in the visual cortices of awake and anesthetized monkeys simultaneously with measurements of single unit activity and the local-field potential. Our results show that in the anesthetized state spontaneous cortical activity shows larger repertoire of cortical states relative to the previous cat studies. In the monkey cortical states coincided with both sets of ocular dominance domains and all the sets of orientations domains. We found large bias toward the representation of cortical states overlapping the two ocular dominance domains rather than orientation domains. Furthermore, cortical states which resemble ocular dominance columns tend to switch into their corresponding orthogonal states. Unlike the results obtained in anesthetized cats where the coherent length was large, the coherent length of the ongoing activity varied dynamically from about 1 mm2 to the entire imaged area of 36 mm2. We then compared the dynamics found in the anesthetized macaque to that observed in the awake state. The dynamics of ongoing activity in the awake state was significantly different. It was characterized by slow traveling waves of activity at ~1.2Hz. Spontaneous ongoing activity correlated with single unit activity revealed only a few (if any) coherent assemblies resembling a given columnar domain with a shorter coherence length and shorter lifetime then in the anesthetized state. Strikingly most of the coherent patterns we observed were not directly related to any given well defined individual columnar system.
Taking together with previous studies, these results indicates that the nature of ongoing activity in the awake state is significantly different, yet also in the awake state coherent ongoing activity of many cells display highly structured dynamics which may play a central role in cortical processing and behavior.
