Abstract
Transcranial magnetic stimulation (TMS) can interfere with smooth pursuit or with saccades initiated from a fixed position toward a fixed target, but little is known about the effect of TMS on catch-up saccade made to assist smooth pursuit. Here we explored the effect of TMS on catch-up saccades by means of a situation in which the moving target was driven by an external agent, or moved by the participants’ hand, a condition known to decrease the occurrence of catch-up saccade. Two sites of stimulation were tested, the vertex and M1 hand area. Compared to conditions with no TMS, we found a consistent modulation of saccadic activity after TMS such that it decreased at 40-100ms, strongly resumed at 100-160ms, and then decreased at 200-300ms. Despite this modulatory effect, the accuracy of catch-up saccade was maintained, and the mean saccadic activity over the 0-300ms period remained unchanged. Those findings are discussed in the context of studies showing that single-pulse TMS can induce widespread effects on neural oscillations as well as perturbations in the latency of saccades during reaction time protocols. At a more general level, despite challenges and interpretational limitations making uncertain the origin of this modulatory effect, our study provides direct evidence that TMS over presumably non-oculomotor regions interferes with the initiation of catch-up saccades, and thus offers methodological considerations for future studies that wish to investigate the underlying neural circuitry of catch-up saccades using TMS.
Highlights
Transcranial magnetic stimulation (TMS) has been proven a useful technique to investigate noninvasively the neural circuitry underlying eye movements, such as visually guided saccades, and smooth pursuit [1,2]
Saccades are distributed rather uniformly during SELF and EXTERNAL, one can notice some clear modulations of saccadic activity following TMS over M1 or the VERTEX
About 40–100 ms after TMS, saccadic activity drops substantially but strongly resumes within the 60 ms, and lastly decreases again at about 200–300 ms. To investigate this phenomenon in more detail, we have collapsed all the trials and computed the probability that some saccadic activity is observed within each 20ms time bin following TMS
Summary
Transcranial magnetic stimulation (TMS) has been proven a useful technique to investigate noninvasively the neural circuitry underlying eye movements, such as visually guided saccades, and smooth pursuit [1,2]. In reaction time protocols, depending on the timing of TMS with respect to the target appearance and/or expected saccade onset, TMS can sometimes shorten or increase the reactive saccade latency [3,4]. In this context, TMS over brain areas such as the frontal eye field (FEF) [5,6,7], or the cerebellum [8,9] has been shown effective. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
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