Motor cortex excitability during spine shape-judgment in adolescent idiopathic scoliosis: a TMS motor evoked potential study

This study investigated the neurophysiological mechanisms linking visual body perception to motor output in females with adolescent idiopathic scoliosis (AIS), specifically examining how altered body schema influences corticospinal excitability. A two-stage paradigm was employed in participants with AIS and healthy controls. First, psychophysical thresholds for detecting spinal curvature were estimated. Second, single-pulse transcranial magnetic stimulation (TMS) was applied over the primary motor cortex (100-125 ms post-stimulus) to assess motor system reactivity to body-relevant stimuli. Corticospinal excitability was recorded via motor evoked potentials (MEPs) from intrinsic hand muscles as a proxy for motor readiness during the observation of spinal distortions. Results revealed that AIS patients exhibited significantly lower perceptual thresholds than controls, indicating hypersensitivity to spinal curvature that correlated with subjective self-perception (Trunk Appearance Perception Scale; TAPS). TAPS scores did not correlate significantly with participants' Cobb angles, indicating that subjective body schema distortion operates independently of mechanical deformity severity. In addition, TMS revealed that AIS patients reached peak corticospinal excitability at their lower perceptual threshold, whereas healthy controls demonstrated peak excitability only when spinal curvatures exceeded their detection thresholds. These findings suggest that AIS involves an increased corticospinal gain in response to body-relevant stimuli. Rather than serving purely as a detection mechanism, the motor system in AIS exhibits a heightened readiness that is tightly coupled with the perception of spinal distortions. Such sensorimotor reorganization suggests that motor excitability is adaptively recalibrated to the patient's lived physical experience.