Reorganization of the primary motor cortex following lower-limb amputation for vascular disease: a pre-post-amputation comparison
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Purpose: This study compared bilateral corticomotor and intracortical excitability of the primary motor cortex (M1), pre- and post-unilateral transtibial amputation. Method: Three males aged 45, 55, and 48 years respectively who were scheduled for elective amputation and thirteen (10 male, 3 female) healthy control participants aged 58.9 (SD 9.8) were recruited. Transcranial magnetic stimulation assessed corticomotor and intracortical excitability of M1 bilaterally. Neurophysiological assessments were performed 10 (SD 7) days prior to surgery and again at 10 (SD 3) days following surgery. Data were analyzed descriptively and objectively compared to 95% confidence intervals from control data. Results: Prior to amputation, all three patients demonstrated stronger short-latency intracortical inhibition evoked from M1 ipsilateral to the affected limb and reduced long-latency intracortical inhibition evoked from M1 contralateral to the affected limb compared to control subjects. Following amputation, short-latency intracortical inhibition was reduced in both M1s and long-latency intracortical inhibition was reduced for the ipsilateral M1. Single-pulse motor evoked potential amplitude and motor thresholds were similar pre-to-post amputation. Conclusions: Modulation of intracortical excitability shortly following amputation indicates that the cortical environment may be optimized for reorganization in the acute post-amputation period which might be significant for learning to support prosthetic mobility. Implications for Rehabilitation Amputation of a lower-limb is associated with extensive reorganization at the level of the cortex. Reorganization occurs in the acute post-amputation period implying a favorable cortical environment for recovery. Rehabilitation or brain interventions may target the acute pre-prosthetic post-amputation period to optimize recovery.