Abstract

Networks in the brain must rely on powerful mechanism for limiting and prioritizing the input flow in order to prevent information overload. We hypothesize that alpha oscillations provide a mechanism for ordering visual input according to relevance. Gamma oscillations phase-locked to the alpha oscillations serve to keep competing representations apart in time. As a result sweeps representing a short to-do list organized as a temporal phase code is produced in every alpha cycle. Empirical support for such a mechanism using MEG in combination with other techniques will be discussed. In a set of attention and memory studies using MEG we have investigated the role of alpha oscillations for gating of information.

These studies provide converging evidence demonstrating that alpha oscillations are inhibitory in nature and can serve to route the visual input. This is further confirmed by a combined EEG/fMRI studies demonstrating that representational specific information as reflected in the BOLD signal is gated by alpha band activity in visual areas. TMS studies combined with MEG have been used to identify frontal regions involved in the top-down control of oscillations in visual cortex. These studies implicate the frontal eye field in modulating posterior oscillations. A DTI study combined with MEG points to the medial superior longitudinal fasciculus as mediating the top-down control.

Finally both MEG and intracranial animal recordings have revealed that alpha and gamma oscillations indeed are coupled: the phase of the alpha activity modulates the gamma power as required by our theoretical framework.  In short, these studies point to coupled alpha and gamma oscillations as playing an important role for routing and prioritizing the visual information flow.

Jensen, O., Gips, B., Bergmann, T.O., and Bonnefond, M. (2014) Temporal coding organized by coupled alpha and gamma oscillations prioritize visual processing. Trends in Neurosciences 37:357-369.

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