P 54. Top-down control of posterior alpha oscillations by the frontal eye field: An fMRI-guided TMS-MEG study

Abstract

Alpha oscillations in visual cortex serve as a mechanism of attentional enhancement via inhibition of task-irrelevant brain regions (Jensen et al., TICS 2012). Humans are able to direct their attention to one visual hemifield in response to an endogenous cue via the modulation of alpha power in visual areas. This top-down control of spatial attention might be mediated by the frontal eye fields (FEF), a key part of the dorsal fronto-parietal attention network. Importantly, previous research has suggested a right-hemispheric dominance of this network: Damage to right frontal and parietal cortex is a predictor of spatial hemineglect (Thiebaut de Schotten et al., Cereb Cortex 2012) and Transcranial Magnetic Stimulation (TMS) of right FEF has been shown to have perceptual consequences for both hemifields, while left FEF TMS affects only the contralateral hemifield (Grosbras and Paus, EJN 2003). Evaluate the differential role of right and left FEF as sources of top-down control of visuospatial attention via the modulation of posterior alpha power in the ipsi-and/or contralateral visual cortex. Fifteen participants (preliminary dataset) received continuous theta burst stimulation (cTBS) to either left FEF, right FEF or scalp vertex (control) before performing an endogenously cued visual spatial attention task whilst magnetoencephalography (MEG) data were recorded. cTBS is known to inhibit activity in FEF for 30–35 min (Nyffeler et al., Neurosci Lett 2006). Individual FEF target sites were identified using an fMRI-based functional localizer. Preliminary MEG analysis focused on the attentional modulation of posterior alpha power during the cue-target interval. After vertex cTBS, we observed the typical pattern of alpha power decreases contralateral and increases ipsilateral to the target hemifield (Thut et al., J Neurosci 2006, Gould et al., JCN 2011). However, following cTBS to both right and left FEF this modulation appeared to be attenuated, with stronger effects observable in the left hemisphere following right FEF cTBS. We are currently investigating the relation between cTBS-induced changes in posterior alpha power modulation and the participants’ behavioural performance. Functional connectivity measures will be employed to determine cTBS-induced changes in long-range coupling between frontal and visual cortex. cTBS to both right and left FEF causes attenuation of cue-related modulation of posterior alpha oscillations with a stronger effect caused by right FEF cTBS.