Low frequency transcranial magnetic stimulation of right posterior parietal cortex reduces reaction time to perithreshold low spatial frequency visual\xa0stimuli

Seth Elkin-Frankston,Antoni Valero-Cabré,Richard J Rushmore

doi:10.1038/s41598-020-59662-4

Abstract

Research in humans and animal models suggests that visual responses in early visual cortical areas may be modulated by top-down influences from distant cortical areas, particularly in the frontal and parietal regions. The right posterior parietal cortex is part of a broad cortical network involved in aspects of visual search and attention, but its role in modulating activity in early visual cortical areas is less well understood. This study evaluated the influence of right posterior parietal cortex (PPC) on a direct measure of visual processing in humans. Contrast sensitivity (CS) and detection response times were recorded using a visual detection paradigm to two types of centrally-presented stimuli. Participants were tested on the detection task before, after, and 1 hour after low-frequency repetitive transcranial magnetic stimulation (rTMS) to the right PPC or to the scalp vertex. Low-frequency rTMS to the right PPC did not significantly change measures of contrast sensitivity, but increased the speed at which participants responded to visual stimuli of low spatial frequency. Response times returned to baseline 1-hour after rTMS. These data indicate that low frequency rTMS to the right PPC speeds up aspects of early visual processing, likely due to a disinhibition of the homotopic left posterior parietal cortex.

Highlights

Research in humans and animal models suggests that visual responses in early visual cortical areas may be modulated by top-down influences from distant cortical areas, in the frontal and parietal regions
We used a mixed model with repetitive transcranial magnetic stimulation (rTMS) time point ‘rTMS Time’ as a repeated measure and stimulation site ‘Stim Site’ as a main factor
Since the task used sequential presentation of visual stimuli, we included stimulus presentation order ‘Flash Number’ (T1 or T2) as a factor to test whether reaction times varied depending on the presentation order of the visual stimulus, and if so, whether this order interacted with rTMS time point ‘rTMS Time’ or with rTMS stimulation site ‘Stim site’

Summary

Introduction

Research in humans and animal models suggests that visual responses in early visual cortical areas may be modulated by top-down influences from distant cortical areas, in the frontal and parietal regions. Response times returned to baseline 1-hour after rTMS These data indicate that low frequency rTMS to the right PPC speeds up aspects of early visual processing, likely due to a disinhibition of the homotopic left posterior parietal cortex. Transcranial magnetic stimulation (TMS), a technique that non-invasively modulates specific brain areas and their associated networks[25] has supported these results and provided evidence that extrastriate visual regions and PPC exert top-down control over early visual areas[19,20,26]. We used a task designed to test basic visual function – contrast sensitivity of a centrally-located Gabor stimulus at 3 cycles per degree (cpd) and at 12 cpd spatial frequencies Performance on this test was evaluated before and after the delivery of inhibitory 1 Hz repetitive Transcranial Magnetic Stimulation (rTMS) to the right posterior parietal cortex. Since a major target of the dorsal visual stream is the posterior parietal cortex[22,38,39], we hypothesized that top-down influences from the PPC would selectively reduce the contrast sensitivity of the lower but not higher spatial frequency stimuli

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