Induction of plasticity in the human motor cortex by pairing an auditory stimulus with TMS

Abstract

Acoustic stimuli can cause a transient increase in the excitability of the motor cortex. The current study leverages this phenomenon to develop a method for testing the integrity of auditorimotor integration and the capacity for auditorimotor plasticity. We demonstrate that appropriately timed transcranial magnetic stimulation (TMS) of the hand area, paired with auditorily mediated excitation of the motor cortex, induces an enhancement of motor cortex excitability that lasts beyond the time of stimulation. This result demonstrates for the first time that paired associative stimulation (PAS)-induced plasticity within the motor cortex is applicable with auditory stimuli. We propose that the method developed here might provide a useful tool for future studies that measure auditory-motor connectivity in communication disorders.

Keywords: auditory cortex; auditory motor integration; motor cortex; paired associative stimulation; plasticity; speech sounds; transcranial magnetic stimulation.

Figure 1

Two sounds used as auditory stimuli. (A) The word “Hey!” and (B) signal correlated noise version of (A). Frequency spectra of the two auditory stimuli. (A) The word “Hey!” and (B) signal correlated noise (white noise) version of (A).

Figure 2

Normalized averaged MEP amplitudes (+SEM) at different times relative to the conditioning auditory stimulus. (A) MEP amplitudes for the condition “noise” for all ISIs (n = 12). (B) MEP amplitudes for the condition “speech sound”. Baseline is represented by the red horizontal line. * denotes average amplitude significantly different from baseline (p < 0.05).

Figure 3

Averaged post- and post15-MEP-amplitudes (+SEM) as percentage of baseline (n= 10). Baseline is represented by the red horizontal line. * denotes average amplitude significantly different from baseline (* < 0.05, ** < 0.01).