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Yong-Jun Lin, Lavanya Shukla, Laura Dugué, Antoni Valero-Cabré, Marisa Carrasco; TMS entrains occipital alpha activity: Individual alpha frequency predicts inter-trial phase coherence. Journal of Vision 2021;21(9):2934. doi: https://doi.org/10.1167/jov.21.9.2934.
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Background: Parieto-occipital alpha rhythms (8-12 Hz) have been shown to underlie cortical excitability and influence visual performance. At rest, each individual has a peak intrinsic alpha frequency (IAF) of these rhythms. However, how the occipital cortex responds to an externally imposed alpha rhythm via transcranial magnetic stimulation (TMS) is an open question. Hypotheses: 10-Hz rhythmic TMS can entrain intrinsic alpha oscillators in the occipital cortex. Specifically, we predicted: (1) progressive enhancement of entrainment across time windows, (2) output frequency specificity, (3) dependence on the intrinsic oscillation phase, and (4) input frequency specificity to individual alpha frequency (IAF) in the neural signatures. Methods: We delivered 4-pulse rhythmic TMS at 10 Hz to entrain local neural activity targeting the right hemisphere V1/V2 regions while participants performed a visual orientation discrimination task. Concurrent electroencephalogram (EEG) recorded TMS-driven changes of local oscillatory activity. There were two control conditions: arrhythmic-active and rhythmic-sham stimulation, both with an equal number of pulses and duration. Results: The results were consistent with the first three hypotheses. Relative to both controls, rhythmic TMS bursts significantly entrained local neural activity. Near the stimulation site, evoked oscillation amplitude and inter-trial phase coherence (ITPC) was increased for 2 and 3 cycles, respectively, after the last TMS pulse. Critically, regarding hypothesis 4, ITPC following entrainment positively correlated with IAF, rather than with the degree of similarity between IAF and the input frequency (10 Hz). Entrainment did not affect visual sensitivity or criterion. Conclusions: We entrained alpha-band activity in occipital cortex for ~3 cycles (~300 ms) with our 4-pulse 10 Hz TMS protocol. IAF predicts the extent of entrained occipital alpha phase synchrony indexed by ITPC.
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