Scientific Understanding of Consciousness
Consciousness as an Emergent Property of Thalamocortical Activity

Modulation of Neuronal Interactions Through Neuronal Synchronization


The following study report published in Science states that groups of activated neurons synchronize in the gamma-frequency band (30 to 100 Hz), and previous studies have related gamma-band synchronization to several cognitive functions. Yet, if gamma-band synchronization subserves those functions, it must have mechanistic consequences for neuronal processing. It has been shown that the precise timing of pre- and postsynaptic activation determines long-term changes in synaptic strength and that gamma-band synchronization of synaptic inputs directly enhances their effective synaptic strength.

The study further states that synchronization between two groups of neurons is also likely to facilitate interactions between them. Gamma-band synchronization entails rhythmic inhibition of the local network, and the periods between inhibition provide temporal windows for neuronal interaction. Two groups of neurons will therefore probably have a greater influence on each other when their temporal interaction windows open at the same times, i.e., when the rhythmic synchronization within the groups is also synchronized between the groups.


Science 15 June 2007: Vol. 316. no. 5831, pp. 1609 - 1612

Modulation of Neuronal Interactions Through Neuronal Synchronization

Thilo Womelsdorf,1 Jan-Mathijs Schoffelen,1 Robert Oostenveld,1 Wolf Singer,2,3 Robert Desimone,4,5 Andreas K. Engel,6 Pascal Fries1,7

1 F. C. Donders Centre for Cognitive Neuroimaging, Radboud University Nijmegen, 6525 EN Nijmegen, Netherlands.
2 Department of Neurophysiology, Max Planck Institute for Brain Research, 60528 Frankfurt, Germany.
3 Frankfurt Institute for Advanced Studies, Johann Wolfgang Goethe University, 60438 Frankfurt, Germany.
4 Laboratory of Neuropsychology, National Institute of Mental Health, National Institutes of Health, Bethesda, MD 20892, USA.
5 McGovern Institute for Brain Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
6 Department of Neurophysiology and Pathophysiology, University Medical Center Hamburg-Eppendorf, 20246 Hamburg, Germany.
7 Department of Biophysics, Radboud University Nijmegen, 6525 EZ Nijmegen, Netherlands.


Brain processing depends on the interactions between neuronal groups. Those interactions are governed by the pattern of anatomical connections and by yet unknown mechanisms that modulate the effective strength of a given connection. We found that the mutual influence among neuronal groups depends on the phase relation between rhythmic activities within the groups. Phase relations supporting interactions between the groups preceded those interactions by a few milliseconds, consistent with a mechanistic role. These effects were specific in time, frequency, and space, and we therefore propose that the pattern of synchronization flexibly determines the pattern of neuronal interactions.

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Studies such as these support the hypothesis that synchronization between neuronal functional groups binds together the functions of the groups. The 40 Hz oscillations and synchronization espoused by Llinás are consistent with these research results.