Transcranial magnetic stimulation to early visual cortex modulates binocular rivalry

Neuromodulation techniques have been pivotal for mapping neural networks. Among these, repetitive transcranial magnetic stimulation (rTMS) is a non-invasive technique that has proven effective in promoting neuroplasticity in various brain regions. Continuous theta burst stimulation (cTBS) is a form of rTMS thought to promote inhibitory effects in primary motor cortex. Our study extends the exploration of cTBS to the visual domain, investigating its impact on binocular rivalry (BR) after administering 600 pulses at 80% of phosphene threshold (PT) to primary visual cortex (V1). Binocular rivalry is characterised by alternating periods of visual dominance when two different images are presented simultaneously to each eye. BR is orchestrated by a complex interplay across the visual pathway, from retinal input to lower and higher cortical processing (including attention). Notably, cortical columns in V1 exhibit monocular responses that underpin the perceptual alternations witnessed in BR, however, the exact mechanism is not well understood. In our sham-controlled study, 19 individuals underwent a BR task, observing orthogonal grey-scale gratings with fixed orientation (+/-45°) through a mirror stereoscope and reporting shifts in visual dominance. Following cTBS application to the left V1 using stereotaxic neuronavigation, participants reported the frequency of BR alternations. Our preliminary findings reveal an increased alternation rate in BR after active cTBS (and not sham), suggesting that cTBS can modulate perceptual dominance in visual processing. These insights enhance our comprehension of cTBS's neuromodulatory potential and underscore its promise as a tool for research and potential treatment of vision disorders rooted in neural dysfunction. Our research contributes to the expanding dialogue on the intersection of neuromodulation, visual perception, and cortical plasticity.