Is one motor cortex enough for two hands?

We report on a patient with mirror movements sustained by a mono-hemispheric fast control of bilateral hand muscles and normal hand function. Transcranial magnetic stimulation of the right motor cortex evoked contractions of muscles in both hands while no responses were observed from the left hemisphere. Somatosensory-evoked potentials, functional magnetic resonance, and diffusion tractography showed evidence of sensorimotor dissociation and asymmetry of corticospinal projections, suggestive of reorganization after early unilateral left brain lesion. This is the first evidence that, in certain rare conditions, good hand function is possible with ipsilateral corticospinal reorganization, supporting the role of unexplored mechanisms of motor recovery.