Journal
CEREBRAL CORTEX
Volume 18, Issue 9, Pages 2010-2018Publisher
OXFORD UNIV PRESS INC
DOI: 10.1093/cercor/bhm229
Keywords
electroencephalography (EEG); phosphene; state dependency; transcranial magnetic stimulation (TMS); visual perception
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Funding
- Swiss National Science Foundation [3200B0-105867]
- Leenaards Foundation
- Ernst and Luice Schmidheiny Foundation
- National Institutes of Health [K24 RR018875, RO1 EY12091, R21 EY0116168]
- International Human Frontiers Science Program Organization
- Centre d'Imagerie BioMedicale (CIBM)
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Neural activity fluctuates dynamically with time, and these changes have been reported to be of behavioral significance, despite occurring spontaneously. Through electroencephalography (EEG), fluctuations in a-band (8-14 Hz) activity have been identified over posterior sites that covary on a trial-by-trial basis with whether an upcoming visual stimulus will be detected or not. These fluctuations are thought to index the momentary state of visual cortex excitability. Here, we tested this hypothesis by directly exciting human visual cortex via transcranial magnetic stimulation (TMS) to induce illusory visual percepts (phosphenes) in blindfolded participants, while simultaneously recording EEG. We found that identical TMS-stimuli evoked a percept (P-yes) or not (P-no) depending on prestimulus alpha-activity. Low prestimulus alpha-band power resulted in TMS reliably inducing phosphenes (P-yes trials), whereas high prestimulus alpha-values led the same TMS-stimuli failing to evoke a visual percept (P-no trials). Additional analyses indicated that the perceptually relevant fluctuations in alpha-activity/visual cortex excitability were spatially specific and occurred on a subsecond time scale in a recurrent pattern. Our data directly link momentary levels of posterior alpha-band activity to distinct states of visual cortex excitability, and suggest that their spontaneous fluctuation constitutes a visual operation mode that is activated automatically even without retinal input.
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