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: Finally, we turn to the EEG-TMS trials from experiment 2. Rate of phosphene perception for occipital TMS at the seven time points after the sound (plus no-sound baseline) is shown in Figure 3A, illustrating its cyclical pattern (blue sinusoid represents best fitting sine wave; 9.1 Hz, Rsquare: 96% of variance explained). Phosphene rate varied in relation to the sound (F(7,56) = 2.77; p = 0.015), being higher at 75–105 ms delays, then again at 195–225 ms, as compared to TMS without any preceding sound (all p < 0.05 on Bonferroni corrected t test). This reproduces the cyclical phosphene finding from experiment 1. Using EEG data on the same trials, we then estimated visual cortex reactivity to the TMS pulse as a function of delay from sound onset (and thus analogous to the phosphene rate analysis). To this end, we calculated for each condition event-related alpha power changes over occipitoparietal sensors, a measure of visual induced activity (cf. .), in a time window for which phosphene perception-related activity has previously been reported (; i.e., 100–200 ms post-TMS), relative to presound baseline (see Experimental Procedures). Note that alpha power is considered to be inversely related to visual cortex activity (smaller values indicate higher reactivity; e.g., ) and hence might also show a cyclical pattern that could relate to that found for phosphene perception. As Figure 3B shows, this pattern was indeed confirmed. There was a significant cyclical pattern in relation to sound onset also for EEG-probed visual cortex reactivity (F(7,56) = 5.91; p < 0.00005, blue sinusoid represents best fitting sine wave; 8.6 Hz, Rsquare: 81% of variance explained). Visual cortex reactivity was significantly higher (corresponding to reduced alpha power) between 75–105 and 195–225 ms after the sound, as compared to the no-sound baseline, or to the 30, 150, or 270 ms delays (all p < 0.05 on Bonferroni corrected t tests). Again, for another view on the same data, we correlated EEG-probed visual cortex reactivity with the rate of phosphene perception across conditions within the same experiment 2. Results of this correlation showed that phosphene perception increased with visual cortex reactivity (i.e., as alpha power decreased) (r(7) = −.95, p < 0.0003); see Figure 3C.
Affiliation: Institute of Neuroscience and Psychology, University of Glasgow, 58 Hillhead Street, Glasgow G12 8QB, UK. firstname.lastname@example.org