Multimodal response-predictor analysis for three non-invasive brain stimulation protocols.

Area of Science:

• Neuroscience
• Neurophysiology
• Brain Stimulation

Background:

• Non-invasive brain stimulation (NIBS) methods like paired associative stimulation (PAS), transcranial direct current stimulation (tDCS), and transcranial alternating current stimulation (tACS) modulate brain activity.
• Significant inter-individual variability exists in responses to NIBS, particularly over the primary motor cortex hand area (M1_hand).

Purpose of the Study:

• To identify baseline neurophysiological, neuroanatomical, and neurochemical predictors of response to PAS, tDCS, and tACS.
• To investigate if factors like late I-wave latency, M1_hand cortical thickness, and corticospinal tract fractional anisotropy predict NIBS outcomes.

Main Methods:

• Healthy participants received PAS, anodal tDCS, and 20-Hz tACS in a repeated measures design.
• Corticospinal excitability changes were measured using transcranial magnetic stimulation input-output curves.
• Primary predictors included late I-wave latency, M1_hand cortical thickness, and CST_hand fractional anisotropy; secondary analyses explored additional MRI and MRS measures.

Main Results:

• None of the primary baseline variables predicted intervention outcomes for any NIBS protocol.
• Exploratory analyses showed no significant correlation between predictors and PAS outcomes.
• tDCS and tACS showed significant correlations with some baseline measures, but these require confirmation.

Conclusions:

• Baseline characteristics do not reliably predict cortical excitability modulation by common NIBS protocols.
• Further research is needed to understand the mechanisms of action for NIBS.
• Exploratory findings require validation in larger, confirmatory studies.