OBJECTIVE: To determine the mechanisms underlying the mirroring of distal movements in both upper and lower limbs present in one individual from birth. METHODS: Transcranial magnetic stimulation (TMS), magnetic resonance imaging (MRI), functional magnetic resonance imaging (fMRI), voluntary and reflexly evoked electromyograms (EMG) and force measurements were used to obtain information about the motor pathways responsible for the mirror movements. RESULTS: MRI showed a significant loss of brain tissue from one hemisphere and fMRI indicated a significant functional reorganization had taken place. An obligatory mirroring of voluntary movement on the sound side occurs on the affected side, but some independent movement can be produced on the affected side, if enabled by weak contractions on the sound side. TMS mapping revealed bilateral projections from one hemisphere and virtually absent projections from the primary motor cortex of the other hemisphere. Spinal reflexes were restricted to the stimulated side. Transcortical reflexes were evoked bilaterally from the sound side, but not from the affected side. CONCLUSIONS: The physiological and imaging data are consistent with a mirroring from the intact motor cortex via the supplementary motor area. SIGNIFICANCE: Mirror movements in this individual represent a major cortical reorganization and a partial solution to the neonatal loss of substantial amounts of brain tissue.
OBJECTIVE: To determine the mechanisms underlying the mirroring of distal movements in both upper and lower limbs present in one individual from birth. METHODS: Transcranial magnetic stimulation (TMS), magnetic resonance imaging (MRI), functional magnetic resonance imaging (fMRI), voluntary and reflexly evoked electromyograms (EMG) and force measurements were used to obtain information about the motor pathways responsible for the mirror movements. RESULTS: MRI showed a significant loss of brain tissue from one hemisphere and fMRI indicated a significant functional reorganization had taken place. An obligatory mirroring of voluntary movement on the sound side occurs on the affected side, but some independent movement can be produced on the affected side, if enabled by weak contractions on the sound side. TMS mapping revealed bilateral projections from one hemisphere and virtually absent projections from the primary motor cortex of the other hemisphere. Spinal reflexes were restricted to the stimulated side. Transcortical reflexes were evoked bilaterally from the sound side, but not from the affected side. CONCLUSIONS: The physiological and imaging data are consistent with a mirroring from the intact motor cortex via the supplementary motor area. SIGNIFICANCE: Mirror movements in this individual represent a major cortical reorganization and a partial solution to the neonatal loss of substantial amounts of brain tissue.