Modulation of Visual Cortex Excitability by Continuous Theta Burst Stimulation Depends on Coil Type

• Published in: PloS one Vol. 11; no. 7; p. e0159743
• Main Authors: Brückner, Sabrina, Kammer, Thomas
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 26.07.2016; Public Library of Science (PLoS)
• Subjects: Achievement tests; Adult; Analysis; Biology and Life Sciences; Bursting; Coils; Correlation analysis; Electroencephalography - instrumentation; Electroencephalography - methods; Electroencephalography - standards; Excitability; Female; Humans; Male; Medicine and Health Sciences; Modulation; Neural Inhibition; Phosphene; Phosphenes; Psychophysics; Research and Analysis Methods; Social Sciences; Stimulation; Stimulus generalization; Stochastic resonance; Stochasticity; Studies; Theta Rhythm; Thresholds; Transcranial magnetic stimulation; Visual cortex; Visual Cortex - physiology; Visual stimuli; Visual thresholds; Germany
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0159743

Subthreshold continuous theta burst stimulation of the visual cortex has been reported to cause inhibitory effects on phosphene threshold. In contrast, we observed no inhibition in a former study applying higher stimulation intensities. The main discrepancies between our experiments and the former studies were stimulation intensity and coil type. We aimed at investigating the role of these factors on the modulatory effects of continuous theta burst stimulation applied to the visual cortex. In a between-group-design, we used either a figure-of-eight-coil or a round coil, respectively. We measured phosphene thresholds prior and after continuous theta burst stimulation applied at 80% of individual phosphene threshold. With the figure-of-eight-coil, phosphene thresholds significantly decreased following stimulation. This is in line with the results of our former study but contrary to the increase observed in the other two studies. Using a round coil, no significant effect was observed. A correlation analysis revealed an inhibitory effect in subjects with higher phosphene thresholds only. Furthermore, the slope of the baseline phosphene threshold seems to predict the direction of modulation, independent from coil type. Thus, modulatory effects of continuous theta burst stimulation seem to depend on coil type and psychophysics parameters, probably due to different cortex volumes stimulated. Stochastic resonance phenomena might account for the differences observed.