Does abnormal branching of inputs to motor neurones explain abnormal muscle cocontraction in cerebral palsy?

The common synaptic drive shared between two groups of motor neurones synch ronizes the timing of discharges between the motor-neurone groups, Recordin gs were made of motor-unit discharges during cocontraction of ipsilateral p airs of thumb muscles in eight subjects with cerebral palsy (CP) aged 4 to 13 years and eight neurologically healthy subjects aged 4 to 12 years, and in pairs of lower-limb muscles in 21 subjects with CP and 21 control subjec ts, both aged 3 to 15 years. Common synaptic drive, likely to be derived at least partly from activity in branched corticospinal-tract neurones, produ ced motor-unit synchronization between pairs of thumb muscles in control su bjects but was absent in all subjects with CP. Motor unit synchronization w as not found between lower-limb antagonist muscles that cocontract abnormal ly in CP, nor was synchronization present in more widely separated muscle p airs. Therefore, abnormal patterns of muscle activation and more widespread muscle reflex responses do not result from an abnormal distribution of com mon synaptic drive in CP.