Abstract
BackgroundSynchronized oscillation in cortical networks has been suggested as a mechanism for diverse functions ranging from perceptual binding to memory formation to sensorimotor integration. Concomitant with synchronization is the occurrence of near-zero phase-lag often observed between network components. Recent theories have considered the importance of this phenomenon in establishing an effective communication framework among neuronal ensembles.Methodology/Principal FindingsTwo factors, among possibly others, can be hypothesized to contribute to the near-zero phase-lag relationship: (1) positively correlated common input with no significant relative time delay and (2) bidirectional interaction. Thus far, no empirical test of these hypotheses has been possible for lack of means to tease apart the specific causes underlying the observed synchrony. In this work simulation examples were first used to illustrate the ideas. A quantitative method that decomposes the statistical interdependence between two cortical areas into a feed-forward, a feed-back and a common-input component was then introduced and applied to test the hypotheses on multichannel local field potential recordings from two behaving monkeys.Conclusion/SignificanceThe near-zero phase-lag phenomenon is important in the study of large-scale oscillatory networks. A rigorous mathematical theorem is used for the first time to empirically examine the factors that contribute to this phenomenon. Given the critical role that oscillatory activity is likely to play in the regulation of biological processes at all levels, the significance of the proposed method may extend beyond systems neuroscience, the level at which the present analysis is conceived and performed.
Highlights
Cortical information processing involves the coordinated activity among many distinct regions of the brain
Studies in animal preparations have shown that stimulus-evoked short-range synchrony between neurons in the primary visual area subserves perceptual binding of sensory information [1,2]
The observation that S1 and 7b play a pivotal role in the organization of the network has led to the hypothesis that the beta network supports the maintenance of lever depression by facilitating sensorimotor integration [11,26,30]
Summary
Cortical information processing involves the coordinated activity among many distinct regions of the brain. This coordinated activity manifests as correlated or synchronized co-variations in the recorded multivariate data. Similar observations have been made [6] where highly synchronized EEG activity occurs in response to stimulus input. In all these cases, a near-zero phase-lag relation between different data series is observed, reflecting the millisecond or even sub-millisecond precision required for feature integration [1,7,8,9]. Recent theories have considered the importance of this phenomenon in establishing an effective communication framework among neuronal ensembles
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