The developing brain is highly plastic and thus brain lesions during development interfere with the innate development of architecture, connectivity and mapping of functions and trigger modifications in structure, wiring and representation. Unilateral inhibition of the sensorimotor cortex during development results in a sparse contralateral projection from this cortex and retention of a greater number of ipsilateral projections from the more active cortex. We report a patient with bilateral cerebral lesions. She had mild hemiparesis. Transcranial magnetic stimulation to the less affected hemisphere elicited bilateral motor evoked potentials of the first dorsal interossei and ipsilateral responses revealed shorter onset latencies and larger peak to peak amplitude than contralateral response, implying a greater ipsilateral than contralateral projection. This observation indicates direct ipsilateral corticospinal projections from the less affected brain hemisphere. (J Korean Acad Rehab Med 2008; 32: 582-585)
