Abstract
Modulatory effects of repetitive transcranial magnetic stimulation (TMS) depend on the activity of the stimulated cortical area before, during, and even after application. In the present study, we investigated the effects of theta burst stimulation (TBS) on visual cortex excitability using phosphene threshold (PTs). In a between-group design either continuous or intermittent TBS was applied with 100% of individual PT intensity. We varied visual demand following stimulation in form of high demand (acuity task) or low demand (looking at the wall). No change of PTs was observed directly after TBS. We found increased PTs only if subjects had high visual demand following continuous TBS. With low visual demand following stimulation no change of PT was observed. Intermittent TBS had no effect on visual cortex excitability at all. Since other studies showed increased PTs following continuous TBS using subthreshold intensities, our results highlight the importance of stimulation intensity applying TBS to the visual cortex. Furthermore, the state of the neurons in the stimulated cortex area not only before but also following TBS has an important influence on the effects of stimulation, making it necessary to scrupulously control for activity during the whole experimental session in a study.
Highlights
Applying pulses of transcranial magnetic stimulation (TMS) to the occipital pole can result in elementary visual percepts called phosphenes (Barker et al, 1985; Meyer et al, 1991; Marg and Rudiak, 1994)
We expected the following effects: (a) theta burst stimulation (TBS) will modify phosphene threshold (PTs); (b) the modulation of PT will last for some time if subjects have low visual demand following TBS; and (c) the modulation will be affected if subjects have high visual demand following TBS
The two baseline values in each of the two sessions were subjected to an omnibus repeated-measures analysis of variance (rmANOVA) with the between-factor GROUP and the within-factors MEASUREMENT (1 and 2) and SESSION
Summary
Applying pulses of transcranial magnetic stimulation (TMS) to the occipital pole can result in elementary visual percepts called phosphenes (Barker et al, 1985; Meyer et al, 1991; Marg and Rudiak, 1994). Quite a few studies have stated that PT is a stable parameter for visual cortex excitability, showing low test-retest-variability within the same subject (e.g., Boroojerdi et al, 2000a, 2002; Stewart et al, 2001; Antal et al, 2003; Siniatchkin et al, 2011). Boroojerdi et al (2000a) showed reduced PTs following light deprivation, indicating a substantial increase in visual cortex excitability. In contrast to such a binocular deprivation, it was shown that monocular deprivation acutely triggers a reversible decrease in visual cortex excitability (Lou et al, 2011)
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