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Eric Maris - Neuronal information processing by structured phase heterogeneity

22 november 2011

Groups of neurons tend to synchronize in distinct frequency bands. Within a given frequency band, synchronization is defined as the consistency of phase relations between site pairs, over time. This synchronization has been investigated in numerous studies and has been found to be modulated by sensory stimulation or cognitive conditions.

Although synchronization is likely to be relevant for the function of neuronal networks, extended synchronization across neuronal space prohibits flexibility and differentiation in information processing. Therefore, synchronization should be local. One structure that achieves local synchronization involves oscillations that are coherent but not zero-phase-synchronous across space. That is, spatially distributed oscillatory networks with systematic phase differences (phase relations). In two studies, we investigated the existence and possible functional role of diversity in these phase relations.

In the first study, we investigate local field potentials (LFPs) and multi-unit activity (MUA) recorded from area V4 of two monkeys performing a selective visual attention task. We show that phase relations, that are consistent over time, are typically diverse across site pairs. That is, across site pairs, phase relations differ substantially and this across-site-pair phase-relation diversity is highly reliable. Furthermore, we show that visual stimulation and selective attention can shift the pattern of phase relations across site pairs. These shifts are again diverse and this across-site-pair phase-relation-shift diversity is again highly reliable.

In the second study, we investigated phase-amplitude coupling (PAC), the phenomenon that high-frequency amplitudes have a consistent phase relation with some low-frequency oscillation. PAC is a possible mechanism for selectively routing information through neuronal networks. If so, then phase diversity over space determines its selectivity. To investigate this issue, we analyzed human electrocorticographic (ECoG) recordings while patients were performing a working memory task. We demonstrate that (1) spatially distributed PAC occurred at distances over 10 cm, and (2) involved diverse preferred coupling phases. Using a novel technique (N-way decomposition based on the PARAFAC model), we demonstrate that these diverse phases originated mainly from the phase-providing oscillations. With these properties, PAC can be the backbone of a mechanism that is able to separate spatially distributed networks operating in parallel.
Laatst gewijzigd:04 juli 2014 21:28
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