Andreas Kleinschmidt, Hôpitaux Universitaires de Genève
December 15 2014, 11h Salle de réunion du LPP, H432
Alpha oscillations, alertness and attention
Oscillations near 10 Hz are the single most salient property in population activity of the human brain. Accordingly, they have been called the “alpha” rhythm. Traditionally these oscillations have been taken to indicate cortical idling but recent research has assigned them a more active role. What exactly is this role? Locally, alpha oscillations result in a rhythmic inhibition of neural activity but how this relates to active processing and behavioral benefit is still far from clear.
Some contributions to the understanding of alpha oscillations have emerged from multimodal approaches and in particular from simultaneous recordings of ongoing brain activity by EEG and fMRI. This avenue has proven interesting because the observation which neuroanatomical structures show activity changes that correlate with alpha oscillations can also inform hypotheses about the function of alpha oscillations. At least three so-called resting-state networks seem to correlate in their activity with fluctuations in different features of alpha oscillations. Based on such findings we have proposed the “windshield wiper” model according to which the functional role of alpha oscillations is to cyclically clear accumulated cortical information. As a consequence, alpha activity can bias cortical processing in favor of strong and recent signals. We postulate that this is a suitable mechanism for a low-level attentional function, that of tonic alertness. Moreover, we have shown a direct functional consequence of rhythmic inhibition on cortical processing, namely that responses evoked by brief sensory stimuli are modulated by the phase of the alpha cycle during which stimulation occurs. Strong evoked responses despite high ongoing alpha activity hence presumably require sustained and/or salient sensory input. Conversely, whenever priors permit the deployment of selective attention, this leads to the disabling of alpha activity in specific channels that are likely to convey the attended information. Whether alpha activity facilitates or impedes behavioral performance will hence depend on the neural sites where it manifests and the cognitive context within which it occurs, thus reconciling apparent discrepancies in the literature.