Intrahemispheric theta rhythm desynchronization impairs working memory

Alekseichuk, Ivan, Stefanie Corinna Pabel, Andrea Antal, and Walter Paulus. 2017. 'Intrahemispheric theta rhythm desynchronization impairs working memory', Restorative neurology and neuroscience, 35: 147-58.
 
Summary:        Synchronization between the left and right hemisphere has been shown to correlate with improved performance in a variety of cognitive and motor tasks. Alekseichuk et al. delivered transcranial alternating current stimulation (tACS) in theta frequency (6Hz) to four locations on the scalp, left and right frontal and parietal cortex, to either synchronize within hemisphere or across hemispheres during performance of a working memory task. Only stimulation that desynchronized the hemispheres disrupted performance – increased reaction time and decreased accuracy – relative to placebo and no stimulation. EEG taken after the task found a decrease in function connectivity across the scalp from desynchronizing tACS. These findings provide causal evidence for the role of interhemispheric connectivity in working memory processing.
 
Pros:

• Unique stimulation paradigm that leveraged the natural desynchronizing and synchronizing aspects of tACS
• The use of functional connectivity analysis in EEG was ideal for measuring target engagement

 
Open questions:

• Does the difference in electric field between the stimulation modalities alter interpretation of the results?
• Why was synchronizing tACS not successful in boosting working memory performance? The study inherently tests two factors simultaneously within hemisphere connectivity and between hemisphere connectivity.

 
Contributed by: Justin Riddle, PhD