Effects of theta transcranial alternating current stimulation over the frontal cortex on reversal learning

Wischnewski, Miles, Paul Zerr, and Dennis JLG Schutter. 2016. 'Effects of theta transcranial alternating current stimulation over the frontal cortex on reversal learning', Brain stimulation, 9: 705-11.
 
Summary:        Theta oscillations are generated after notification of a reward or loss in reinforcement learning paradigms. Wischnewski et al., delivered theta-frequency transcranial alternating current stimulation (tACS) bifrontally during performance of a reward-based reinforcement learning task. Participants that receive theta-tACS were quicker to learn that a decision was less rewarding and quicker to re-learn its value when it was re-instated as rewarding. EEG results revealed that theta-tACS decreased theta oscillations (and theta-beta ratio) as measured by rest after versus before the task. These results provide causal evidence for theta oscillations in reward learning.
 
Pros:

• Cognitive task and behavioral modeling was well-done and reflected the clear hypotheses of the experimenters
• The use of resting-state EEG to measure the aftereffect of stimulation was valuable to demonstrate target engagement

 
Open questions:

• Why did theta-tACS decrease theta oscillations are the stimulation?
• Stimulation used a two electrode montage that theoretically de-synchronized the frontal cortices. How does this factor into the interpretation of the task given that purported left-hemisphere dominance of the task?

 
Contributed by: Justin Riddle, PhD