Dynamic cortical cooperation related to visual perception

We have continued testing the hypothesis of visual feature-binding by synchronization inγ monkey visual cortex. Current support for this hypothesis comes from recent results demonstrating local synchrony among rhythmic or stochastic γ-activities (30-90Hz) - including their perceptual modulation - and decoupling of γ-activity among neural groups representing figure and background. On the other hand, γ-synchrony in primary visual cortex is restricted to few millimeters, which challenges the binding-by-synchronization hypothesis for larger cortical distances. But we found that this restriction is due to extended traveling γ-waves, randomly altering their directions. Thus, across intermediate distances, phase continuity of these waves may still support coding of object continuity. Finally, across large distances we observed cortico-cortical interactions among low frequency signals and the envelopes of amplitude-modulated γ-signals. We discuss potential mechanisms of near-, medium- and far-range cooperativity on the basis of spike-coding model networks. They include two types of inhibitory feedback loops generating local γ-activities and low-frequency modulations, respectively. In conclusion, we propose that the binding-by-synchronization hypothesis, initially restricted to synchrony of oscillatory γ-signals, be extended to more general forms of signal coupling, including near-range phase synchrony (coherence) between γ-activities, medium-range phase continuity of γ-waves, and far-range coupling involving low-frequency signals and envelopes of γ-signals.