T117. The effects of Transcranial Alternating Current Stimulation (tACS) at Individual Alpha Peak Frequency (iAPF) on motor cortex excitability of young and elderly adults

Introduction Transcranial alternating current stimulation (tACS) was shown to modulate brain oscillation, cortical excitability and behaviour. This technique allows for the direct perturbation of brain oscillation such as the EEG alpha wave (8–12 Hz). In aging, there is correlation between the decrease in alpha activity and the profound cognitive and motor impairments. Studies suggest a state-dependent effect of tACS on alpha activity: upregulation of alpha oscillations only occurs in conditions of low alpha power (e.g. in the elderly). Methods The present study aimed at further exploring the state-dependent effect of tACS on cortical excitability. We applied tACS at individual alpha peak frequency (iAPF) for 10 min (1.5 mA) to the left motor cortex of healthy young and old volunteers. Transcranial magnetic stimulation (TMS) was used to assess the changes in cortical excitability as measured by motor evoked potentials (MEP) at rest before and after stimulation. Results TACS increased cortical excitability in both groups. This indicates that the effect was not state-dependent. However, our results also suggest that the mechanism behind the effects was different, as we observed an increase in intracortical inhibition in the old group and a decrease in inhibition in the young group. Conclusion Our results point to tACS as a potential approach to compensate the decline in alpha activity and to improve cognitive and motor function in the elderly.