Research reportHigh-gamma oscillations in the motor cortex during visuo-motor coordination: A tACS interferential study

- High-frequency, imperceptible, electrical stimulation of the motor cortex affects visuo-motor coordination.
- 80 Hz stimulation enhances performance just after sudden changes in tracking trajectory.
- Effects take place between 200 and 500 ms after the onset of a new unexpected motor program.
- Response to tACS suggests a functional role for gamma activity in the motor cortex.

BackgroundWhile the role of beta (∼20 Hz), theta (∼5 Hz) and alpha (∼10 Hz) oscillations in the motor areas have been repeatedly associated with defined properties of motor performance, the investigation of gamma (∼40-90 Hz) oscillatory activity is a more recent and still not fully understood component of motor control physiology, despite its potential clinical relevance for motor disorders.Objective/hypothesisWe have implemented an online neuromodulation paradigm based on transcranial alternating current stimulation (tACS) of the dominant motor cortex during a visuo-motor coordination task. This approach would allow a better understanding of the role of gamma activity, as well as that of other oscillatory bands, and their chronometry throughout the task.MethodsWe tested the effects of 5 Hz, 20 Hz, 60 Hz (mid-gamma) 80 Hz (high-gamma) and sham tACS on the performance of a sample of right-handed healthy volunteers, during a custom-made unimanual tracking task addressing several randomly occurring components of visuo-motor coordination (i.e., constant velocity or acceleration pursuits, turns, loops).ResultsData showed a significant enhancement of motor performance during high-gamma stimulation - as well as a trending effect for mid-gamma - with the effect being prominent between 200 and 500 ms after rapid changes in tracking trajectory. No other effects during acceleration or steady pursuit were found.ConclusionsOur findings posit a role for high-frequency motor cortex gamma oscillations during complex visuo-motor tasks involving the sudden rearrangement of motor plan/execution. Such a “prokinetic” effect of high-gamma stimulation might be worth to be tested in motor disorders, like Parkinson's disease, where the switching between different motor programs is impaired.