Slow-oscillatory tACS does not modulate human motor cortical response to repeated plasticity paradigms

Area of Science:

• Neuroscience
• Neuroplasticity
• Sleep Research

Background:

• Synaptic plasticity, crucial for learning and memory, can saturate with repeated activity.
• The synaptic homeostasis hypothesis posits that slow-wave sleep restores plasticity by downscaling synaptic potentiation.
• The specific role of slow-oscillatory neural activity, independent of sleep, in human synaptic homeostasis remains unclear.

Purpose of the Study:

• To investigate whether slow-oscillatory transcranial alternating current stimulation (tACS) in awake humans can induce synaptic homeostasis.
• To determine if tACS can prevent homeostatic interference between successive plasticity-inducing interventions (motor learning and paired associative stimulation).
• To test the hypothesis that slow-oscillatory tACS facilitates plasticity following motor learning and PAS.

Main Methods:

• Thirty-six participants received sham and active fronto-motor tACS interleaved with motor learning and PAS protocols.
• Electroencephalography (EEG) recorded neural oscillations, and motor evoked potentials (MEPs) quantified synaptic plasticity changes.
• Bayesian statistics were employed to analyze MEP data and assess the effects of tACS.

Main Results:

• Motor training induced significant excitatory plasticity, as expected.
• Active tACS showed moderate evidence against restoring plasticity after PAS.
• No lasting entrainment of slow oscillations was observed in the EEG recordings.

Conclusions:

• Slow-oscillatory tACS, under the tested conditions, did not modulate synaptic homeostasis in the awake human motor system.
• These findings suggest that the full restorative effects of slow oscillations on synaptic plasticity may require the complex state of sleep.
• Further research is needed to elucidate the precise mechanisms underlying synaptic homeostasis and the role of sleep.