Publication
Modulation of Visually Evoked Cortical fMRI Responses by Phase of Ongoing Occipital Alpha Oscillations
Publisher:
Society for Neuroscience
Date:
09-03-2011
DOI:
10.1523/JNEUROSCI.4697-10.2011
Abstract: Using simultaneous electroencephalography as a measure of ongoing activity and functional magnetic resonance imaging (fMRI) as a measure of the stimulus-driven neural response, we examined whether the litude and phase of occipital alpha oscillations at the onset of a brief visual stimulus affects the litude of the visually evoked fMRI response. When accounting for intrinsic coupling of alpha litude and occipital fMRI signal by modeling and subtracting pseudo-trials, no significant effect of prestimulus alpha litude on the evoked fMRI response could be demonstrated. Regarding the effect of alpha phase, we found that stimuli arriving at the peak of the alpha cycle yielded a lower blood oxygenation level-dependent (BOLD) fMRI response in early visual cortex (V1/V2) than stimuli presented at the trough of the cycle. Our results therefore show that phase of occipital alpha oscillations impacts the overall strength of a visually evoked response, as indexed by the BOLD signal. This observation complements existing evidence that alpha oscillations reflect periodic variations in cortical excitability and suggests that the phase of oscillations in postsynaptic potentials can serve as a mechanism of gain control for incoming neural activity. Finally, our findings provide a putative neural basis for observations of alpha phase dependence of visual perceptual performance.