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.

Audiomotor Integration in Minimally Conscious State: Proof of Concept!

“…The clinical and electrophysiological ameliorations in HC and MCS patients mainly depended on the type of the conditioning protocol that was employed, as also previously shown in healthy individuals [ 14 , 19 ]. In fact, neither the rTMS_alone nor the rES_alone induced any significant posteffect.…”

“…In analogy to a previous work [ 14 ], we applied pairs of stimuli consisting of a conditioning stimulus (500 Hz sine tone burst) followed by a magnetic test (90% of AMT), with an interstimulus interval of subject's N1 peak-latency +50 ms [ 20 , 29 , 30 ]. Although it has been reported that speech sounds topographically activate the motor cortex (e.g., [ 21 ]), others suggest that the motor cortex might be also nontopographically activated by nonspeech sounds [ 31 ].…”

“…In addition, it has been shown that some noninvasive neurostimulation protocol could unmask residual covert connectivity patterns in some DOC patients, including UWS [ 13 ]. Recently, paired associative stimulation (PAS) protocol has been employed in shaping the AMI in healthy individuals [ 14 ]. PAS is an electrophysiological technique that pairs conditioning stimuli (e.g., visual, sensory, and auditory stimuli, motor imagery, or movements) with transcranial magnetic stimuli (TMS) over the motor cortex [ 15 – 17 ], thus inducing a long-lasting change in cortical excitability probably by means of Hebbian long-term potentiation or depression-like process (LTP, LTD) [ 18 ].…”

“…PAS is an electrophysiological technique that pairs conditioning stimuli (e.g., visual, sensory, and auditory stimuli, motor imagery, or movements) with transcranial magnetic stimuli (TMS) over the motor cortex [ 15 – 17 ], thus inducing a long-lasting change in cortical excitability probably by means of Hebbian long-term potentiation or depression-like process (LTP, LTD) [ 18 ]. Concerning AMI, conditioning auditory stimuli affect the motor cortex excitability [ 14 ], whereas acoustic stimuli paired with TMS over the auditory cortex induce tonotopically specific and tone-unspecific auditory cortex plasticity [ 19 ]. In addition, speech perception can modulate the motor cortical excitability within hand, lips, and tongue area representation [ 20 – 22 ].…”

Editorial: Current research and emerging directions on the cognitive and neural organization of speech processing

“…Komeilipoor et al ( 2014 ) report higher motor excitability as measured using Transcranial Magnetic Stimulation (TMS) in the tongue area during the presentation of meaningful gestures (noun-associated). Sowman et al ( 2014 ) demonstrate that appropriately timed TMS to 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.…”