Pathophysiology of congenital mirror movements

A case of congenital mirror movements occurring in association with mild hemiparesis and unilateral schizencephaly was investigated using focal transcranial magnetic stimulation. The cortical motor representations for first dorsal interosseous, abductor digiti minimi and biceps brachii were mapped for both cerebral hemispheres: bilateral short latency EMG responses were elicited with stimulation over the nonschizencephalic hemisphere while no short latency responses were obtained with stimulation over the schizencephalic hemisphere. The cortical representations for all three homologous muscle pairs studied were colocalized, and the responses occurred at identical latencies bilaterally. Our findings, plus previous observations suggesting a single functional motor cortex in schizencephaly, are consistent with the suggestion that mirror movements are the result of branched corticospinal projections to distal muscle groups.