State-dependent effects of transcranial oscillatory currents on the motor system during action observation.

Fuerra, Matteo, Evgeny Blagovechtchenski, Vadim V. Nikulin, Maria Nazarova, Anna Lebedeva, Daria Pozdeeva, Maria Yurevich, & Simone Rossi. 2019. State-dependent effects of transcranial oscillatory currents on the motor system during action observation. Scientific Reports. 9: 12858.
 
Summary: This study addresses the question the causal role of specific frequencies in action observation--a cognitive domain which engages the premotor motor cortex and facilitates TMS-induced MEPs. Using a range of tACS protocols (5, 10, 20, & 40 Hz) and an active sham condition, the investigators measured MEPs from the first dorsal interosseus (FDI) and the abductor digiti minimi (ADM) during stimulation under conditions of rest and observation of a hand making a pinching movement (i.e., activating the FDI). TACS delivered at 20 Hz induced a non-selective facilitation of MEPs in both muscles at rest, whereas 10 Hz and 40 Hz tACS only facilitated MEPs in the FDI during movement observation suggesting these frequencies play a role in movement planning and execution. 
 
Pros: 

• Novel paradigm with concurrent tACS-TMS to Address state-dependent effects of tACS
• Wide range of frequencies tested
• Sophisticated set of differential findings. Demonstrated frequency specific effects of tACS on general motor cortex excitability & selective muscle activation

 
Open Questions: 

• How do the pro-movement effects of gamma-band tACS reconcile with the more domain general facilitation of beta-band tACS?

 
Contributed by: Christopher Walker, PhD