Differences between 'congenital mirror movements' and 'associated movements' in normal children: a neurophysiological case study.

In this study we analysed how far physiological associated movements in normal children (which may be present up to the age of 10 years) share the same physiological mechanism with clinically apparent mirror movements. Transcranial magnetic stimulation (TMS) and kinematic movement analysis were applied in a 4-year-old child with congenital mirror movements (CMM). The results were compared with a normative data base of clinically normal children. In the child with CMM focal TMS of one motor cortex induced bilaterally symmetrical responses in distal and proximal upper extremities muscles with identical ipsi- and contralateral latencies. Also kinematic analysis showed a precise symmetrical onset of intended and unintended contralateral movements, whereas normal children with associated movements showed a variable movement onset delay between extremities. The data suggest a different physiological mechanism underlying these two varieties of elementary associated motor activity in childhood.