Sounds reset rhythms of visual cortex and corresponding human visual perception.
Bottom Line: In principle, this may result in stimulus-locked periodicity in behavioral performance.Here we considered this possible cross-modal impact of a sound for one of the best-characterized rhythms arising from the visual system, namely occipital alpha-oscillations (8-14 Hz).This shows that cross-modal phase locking of oscillatory visual cortex activity can arise in the human brain to affect perceptual and EEG measures of visual processing in a cyclical manner, consistent with occipital alpha oscillations underlying a rapid cycling of neural excitability in visual areas.
Affiliation: Institute of Neuroscience and Psychology, University of Glasgow, 58 Hillhead Street, Glasgow G12 8QB, UK. email@example.comShow MeSH
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Mentions: In experiment 2, we acquired concurrent EEG in the same paradigm and the same participants as in experiment 1, but with fewer TMS time points (now 7 rather than 19, see Experimental Procedures) to allow more trials in each condition for EEG analysis and a higher proportion (1/8) of no-TMS trials. Phosphene perception rates were highly correlated between experiments 1 and 2 (r(7) = 0.90; p < 0.003), for the sound-TMS relations that were in common between these two studies, i.e., experiment 2 essentially reproduced the ∼10 Hz cyclical pattern of phosphene perception of experiment 1 (see below for more detailed analysis of this pattern). We next analyzed EEG data from experiment 2, initially for sound-only trials (no TMS) because these can provide a pure measure of phase locking of EEG activity to the critical sound in the absence of TMS (thus without any associated visual percept). Significant 10 Hz phase locking (p < 0.001) to the critical sound was evident not only for sensors overlaying auditory cortex but also over parieto-occipital cortex, from 50 ms to 250 ms following auditory stimulus onset (Figure 2A). Note that none of the frontal electrodes showed significant phase locking. We then calculated the number of trials showing a phase for parieto-occipital electrodes within ±10 degrees of the preferred phase at 100 ms (the time point postsound at which phosphene rate peaked in experiment 1). This measure showed a cyclical pattern, being significantly higher not only around 100 ms (by definition) but also around 200 ms after the sound, as compared to the 150 ms delay or the no-sound baseline (all p < 0.05, Bonferroni corrected); see Figure 2B. This pattern is strikingly reminiscent of the phosphene rate data from the previous experiment (Figure 1) and the correlated phosphene perception rate of the new experiment.
Affiliation: Institute of Neuroscience and Psychology, University of Glasgow, 58 Hillhead Street, Glasgow G12 8QB, UK. firstname.lastname@example.org