Modulation of large-scale cortical coupling by transcranial alternating current stimulation

Schwab, Bettina C, Jonas Misselhorn, and Andreas K Engel. 2019. 'Modulation of large-scale cortical coupling by transcranial alternating current stimulation', Brain stimulation, 12: 1187-96.
 
Summary:        Neural oscillations synchronized between regions is proposed to be a mechanism for information transfer between areas. Schwab et al., delivered alpha-frequency transcranial alternating current stimulation (tACS) either in-phase, anti-phase, or with a randomized and changing phase difference using high-density tACS to bi-occipital cortex. In-phase tACS selectively increased alpha frequency connectivity between the stimulated occipital cortices relative to anti-phase and random-phase was intermediary. Both in-phase and anti-phase equally increased alpha power. Source localization revealed spatial specificity of the connectivity changes to the stimulated regions. The study demonstrates the spatial and temporal power of tACS to modulate the functional connection between brain regions.
 
Pros:

• The use of spatial and temporal analysis was compelling to test the specificity of tACS effects
• Jittered phase tACS is innovative as a control stimulation similar to arrhythmic stimulation in TMS

 
Open questions:

• Were these effects enabled by the presence of intrinsic alpha oscillators in the occipital-parietal cortex?
• Would tACS to two nodes of a network increase functional connectivity across the wider network?

 
Contributed by: Justin Riddle, PhD