The level of selective visual attention is closely related to the intensity of sustained γ band synchronization in early visual areas

Aim: Cortical gamma band synchronization is associated with attention. Accordingly, directing attention to certain visual stimuli modulates gamma band activity in visual cortical areas. However, gradual effects of attention and behavior on gamma band activity in early visual areas have not been reported. By reallocating available resources between simultaneously presented bimodal stimuli graded attention effects can be studied.

Methods: In the present study, the degree of selective visual attention was gradually varied in a cued bimodal reaction time paradigm using audio-visual stimuli. Participants were 16 healthy right handed subjects (8 female, mean age: 25.5±4.3 years; SD) with normal hearing and normal or corrected to normal vision. Brain activity was recorded with magnetoencephalography (MEG) and analyzed with respect to time, frequency, and location of strongest gamma band response.

Results: Reaction times to visual and auditory stimuli reflected three presumed graded levels of visual attention (high, medium, and low; p<0.001). MEG data showed sustained gamma band synchronization in all three conditions in early visual areas (V1 and V2), while the intensity of gamma band synchronization increased with the level of visual attention (from low to high). Differences between conditions were seen for up to 1600ms (p=0.009– p<0.001).

Conclusions: The current results show that in early visual areas the level of gamma band synchronization is related to the level of attention directed to a visual stimulus. These gradual and long-lasting effects, achieved by resource allocation between the visual and auditory modality, expand the biased competition model of attention and highlight the key role of gamma band synchronization in early visual areas for selective attention.