BOLD signal effects of transcranial alternating current stimulation (tACS) in the alpha range: a concurrent tACS–fMRI study

Vosskuhl, Johannes, René J Huster, and Christoph S Herrmann. 2016. 'BOLD signal effects of transcranial alternating current stimulation (tACS) in the alpha range: a concurrent tACS–fMRI study', Neuroimage, 140: 118-25.
 
Summary:        Alpha oscillations are shown to correlate with a reduction in neural activity. However, no prior study demonstrated that alpha frequency transcranial alternative current stimulation (tACS) can reduce neural activity. Vosskuhl et al. deliver alpha frequency tACS to occipital cortex with concurrent fMRI during a visual attention task. In the task, alpha oscillations were hypothesized to decrease and therefore drive an increase in neural activity measured with fMRI. Alpha-tACS resulted in a decrease in task-evoked neural activity. These findings provide causal evidence that alpha-tACS decreases focal neural activity.
 
Pros:

• Use of concurrent tACS and fMRI is innovative for understanding neural mechanism
• Use of individual alpha frequency for tACS personalized the stimulation to each participant

 
Open questions:

• If stimulation was applied to a region in parietal cortex that is presumably the source of attention-modulated alpha oscillations, then would the same effects be found?
• If an oscillation associated with active processing (increased neural excitability) such as theta or gamma were delivered, then would the opposite effect be witnessed?

 
Contributed by: Justin Riddle, PhD