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

Abstract

The common synaptic drive shared between two groups of motor neurones synchronizes the timing of discharges between the motor‐neurone groups. Recordings were made of motor‐unit discharges during cocontraction of ipsilateral pairs 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 subjects, both aged 3 to 15 years. Common synaptic drive, likely to be derived at least partly from activity in branched corticospinal‐tract neurones, produced motor‐unit synchronization between pairs of thumb muscles in control subjects but was absent in all subjects with CP. Motor unit synchronization was not found between lower‐limb antagonist muscles that cocontract abnormally in CP, nor was synchronization present in more widely separated muscle pairs. Therefore, abnormal patterns of muscle activation and more widespread muscle reflex responses do not result from an abnormal distribution of common synaptic drive in CP.

Neuromuscular activation and motor-unit firing characteristics in cerebral palsy

“…A similar result has been found by other investigators in participants with CP and stroke (Datta et al 1991, Farmer et al 1993, Gibbs et al 1999). The reduction is thought to reflect a substantial decrease in the number of direct cortico-motoneuronal connections, which would be consistent with a reduction in strength and dexterity.…”

Neuromuscular mechanisms and neural strategies in the control of time-varying muscle contractions

“…The determination of the frequency and amplitude of force oscillations by volition argues for a supraspinal origin of the frequency-modulated input, a possibility also supported by reported cortical influences on MNs of various muscles (Gibbs et al 1999;Lang and Schieber 2004;McKiernan et al 2000;Palmer and Ashby 1992).…”

Cutaneomuscular reflex responses recorded from the lower limb in children and adolescents with cerebral palsy

“…There is uncertainty about the origin of the rather variable long-latency components that occur after the E2 component (Garnet and Stephens 1980). CMR responses have also been recorded from lower-limb muscles after stimulation of the digital nerves of the second toe (Choa and Stephens 1982, Jenner and Stephens 1982, Rowlandson and Stephens 1985a, Gibbs et al 1995. CMR recorded from distal lower-limb muscles shows a similar configuration to that recorded from intrinsic hand muscles.…”

“…The control children showed a wider distribution of CMR response compared with adults in whom CMR responses were rarely recorded from the ipsilateral quadriceps muscle and never found in the ipsilateral erector spinae muscle while standing (Gibbs et al 1995). A widespread distribution of CMR response in the lower limb has been noted in healthy newborn infants, with responses being recorded from tibialis anterior, soleus, quadriceps, and hamstring muscles after stimulating the digital nerves of a toe (Crum and Stephens 1982).…”