Investigation of Metaplasticity Associated with Transcranial Focused Ultrasound Neuromodulation in Humans

Area of Science:

• Neuroscience
• Neurophysiology
• Noninvasive Brain Stimulation

Background:

• Low-intensity transcranial focused ultrasound stimulation (TUS) is a novel noninvasive brain stimulation (NIBS) technique.
• Theta burst TUS (tbTUS) induces short-term plasticity in the human primary motor cortex (M1).
• Metaplasticity, activity-dependent changes in plasticity, can enhance NIBS efficacy.

Purpose of the Study:

• To investigate the role of metaplasticity and depotentiation in modulating tbTUS-induced plasticity in M1.
• To compare the effects of different NIBS protocol orders on M1 plasticity.

Main Methods:

• Four NIBS protocols were tested: tbTUS alone, cTBS150 alone, cTBS150 followed by tbTUS (metaplasticity), and tbTUS followed by cTBS150 (depotentiation).
• Motor-evoked potentials and intracortical inhibition/facilitation were measured before and after interventions.
• Interventions involved sham and real stimulation delivered in specific sequences.

Main Results:

• Priming M1 with cTBS150 significantly prolonged tbTUS-induced plasticity effects by over 60 minutes.
• Delivering cTBS150 after tbTUS abolished the plasticity effects.
• cTBS150 alone did not induce significant changes; no alterations in M1 intracortical circuits were observed.

Conclusions:

• Metaplasticity can enhance and depotentiation can abolish tbTUS-induced plasticity in the human motor cortex.
• These findings support that tbTUS induces long-term potentiation-like processes.
• Harnessing metaplasticity could optimize therapeutic applications of TUS.