Abstract
BackgroundRepetitive transcranial magnetic stimulation (rTMS) at certain frequencies increases thresholds for motor-evoked potentials and phosphenes following stimulation of cortex. Consequently rTMS is often assumed to introduce a “virtual lesion” in stimulated brain regions, with correspondingly diminished behavioral performance.Methodology/Principal FindingsHere we investigated the effects of rTMS to visual cortex on subjects' ability to perform visual psychophysical tasks. Contrary to expectations of a visual deficit, we find that rTMS often improves the discrimination of visual features. For coarse orientation tasks, discrimination of a static stimulus improved consistently following theta-burst stimulation of the occipital lobe. Using a reaction-time task, we found that these improvements occurred throughout the visual field and lasted beyond one hour post-rTMS. Low-frequency (1 Hz) stimulation yielded similar improvements. In contrast, we did not find consistent effects of rTMS on performance in a fine orientation discrimination task.Conclusions/SignificanceOverall our results suggest that rTMS generally improves or has no effect on visual acuity, with the nature of the effect depending on the type of stimulation and the task. We interpret our results in the context of an ideal-observer model of visual perception.
Highlights
Transcranial magnetic stimulation (TMS) is a powerful, noninvasive method of reversibly altering cortical function
All calculations were performed with the SciPy library for Python. Our goal in these experiments was to characterize the effects of repetitive transcranial magnetic stimulation on performance on various tests of visual perceptual acuity
In particular we were interested in determining how Repetitive transcranial magnetic stimulation (rTMS) delivered at different frequencies changed performance on several discrimination tasks and how these changes were distributed in space and time
Summary
Transcranial magnetic stimulation (TMS) is a powerful, noninvasive method of reversibly altering cortical function. The technique works by inducing a weak electrical current in a brain region that can be selected based on the placement of a magnetic coil near the scalp of the subject Because it is safe and relatively painless the method has found increasing utility as a clinical tool for treating conditions such as Parkinson’s Disease and depression [1], as well as in aiding rehabilitation following stroke [2]. Repetitive TMS (rTMS) involves the application of a series of magnetic pulses over a period of seconds or minutes, with direct effects that last up to an hour [4] and clinical improvements that can accumulate over weeks [5] These effects have been observed primarily in humans through indirect measures of cortical excitability, such as the threshold and amplitude of motor evoked potentials following stimulation of motor cortex [6] and the phosphene threshold following stimulation of visual cortex [7,8]. RTMS is often assumed to introduce a ‘‘virtual lesion’’ in stimulated brain regions, with correspondingly diminished behavioral performance
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