Expected TMS excites the motor system less effectively than unexpected stimulation

Area of Science:

• Neuroscience
• Cognitive Science
• Motor Control

Background:

• The brain predicts sensory input, leading to attenuated responses for self-generated or predicted stimuli.
• Sensory attenuation is proposed to explain why self-tickling is ineffective.
• Transcranial magnetic stimulation (TMS) probes motor system excitability via motor-evoked potentials (MEPs).

Purpose of the Study:

• To investigate if predictive coding principles attenuate neural responses to direct brain stimulation.
• To determine if predictable TMS pulses reduce motor-evoked potential (MEP) amplitudes.

Main Methods:

• Applied TMS over the primary motor cortex to elicit MEPs in peripheral muscles.
• Manipulated TMS pulse predictability through self-initiation and external cueing.
• Compared MEP amplitudes under predictable versus unpredictable TMS conditions.

Main Results:

• MEP amplitudes were significantly attenuated when TMS pulses were predictable (self-initiated or cued).
• This attenuation occurred even without direct motor control over the stimulation.
• Predictability, not motor suppression, was key to reduced MEPs.

Conclusions:

• Predictive coding mechanisms appear to be domain-general, applying to direct brain stimulation.
• These findings support a unified framework for predictive learning across sensory and motor domains.
• Results have methodological implications for controlling predictability in TMS research.