DOES THE LINK BETWEEN SPONTANEOUS MICROSACCADES AND EEG ALPHA OSCILLATIONS DEPEND ON VISUAL INPUTS?

We have previously reported how spontaneous microsaccades – made in the absence of any incentive to look anywhere but a central fixation marker – are associated with the transient lateralisation of posterior 8-12 Hz EEG alpha-band activity according to microsaccade direction (Liu et al., Progress in Neurobiology, 2023). We now ask to what extent such a link between spontaneous microsaccades and EEG-alpha activity depends on visual inputs. If the reported link reflects microsaccades directly, it should be observed irrespective of the concurrent presence or absence of visual inputs. In contrast, if the link reflects a secondary ‘visual consequence’ of microsaccades because microsaccades displace visual inputs across the retina, then the reported link should be contingent on the presence of visual inputs. To address this, we recorded spontaneous microsaccades and EEG activity across three fixation conditions: (1) in the absence of any fixation marker or other visual inputs (i.e. after an initial fixation marker disappeared), (2) in the presence of only a central fixation marker, or (3) in the presence of a central fixation marker together with peripheral visual stimuli. Critically, transient alpha lateralisation following microsaccades was observed even in the condition without the fixation marker and the peripheral stimuli. These data argue for an intrinsic link between the direction of spontaneous microsaccades and the spatially corresponding lateralisation of posterior alpha-band activity.