Transcranial alternating current stimulation reduces BOLD adaptation and increases functional connectivity
Transcranial alternating current stimulation (tACS) is used as a non-invasive tool for cognitive enhancement and clinical applications. The physiological effects of tACS, however, are complex and poorly understood . Most studies of tACS focus on its ability to entrain brain oscillations, but our behavioral results in humans and extracellular recordings in nonhuman primates support the view that tACS at 10 Hz additionally affects brain function by reducing sensory adaptation. Our primary goal
... Our primary goal here was to investigate this using BOLD imaging in human subjects. Hypothesis: 10 Hz tACS applied during a motion adaptation paradigm attenuates the neuronal adaptation reflected in the BOLD signal. Methods: We used a motion adaptation paradigm developed to quantify BOLD adaptation and used standard ANOVA analyses to compare the amount of adaptation in blocks during which tACS was applied to the human motion area (hMT+) to blocks without tACS. In addition, we performed an exploratory analysis to investigate whether tACS affected the functional connectivity of hMT+. Results: tACS significantly attenuated BOLD adaptation and increased functional connectivity between the stimulated hMT+ and the rest of the brain, in particular the dorsal attention network (DAN). Conclusion: Weak 10 Hz currents applied to the scalp change the BOLD signal. Within the targeted area, these changes are compatible with the hypothesis that tACS attenuates neuronal adaptation; similar to what we previously reported based on extracellular recordings. In addition, our findings show that tACS results in increased global brain connectivity of the stimulated area.