OVERACTIVITY OF CERVICAL PREMOTOR NEURONS IN PARKINSONS-DISEASE

Objectives-Cortical command to upper limb motor neurons is transmitted , in humans, not only through the monosynaptic corticomotor neuronal p athway, but also through cervical premotor neurons. Whether activity i n this non-monosynaptic corticospinal pathway is modified in Parkinson 's disease was explored. Methods-Ongoing EMG activity recorded in wris t extensors during tonic extension of the wrist is suppressed by a vol ley evoked by stimulating the superficial radial serve. it has been sh own Chat this cutaneous induced suppression is due to inhibition of tr ansmission of the cortical command at a premotor neuronal level, By co mparing the cutaneous induced EMG depression between 45 de novo parkin sonian patients and 23 age matched controls it has been possible to ap preciate if and to what extent the ''non-monosynaptic'' part of the co rtical command is modified in these patients. Results-At the early sta ge of the illness the EMG depression, reflecting the ''non-monosynapti c'' part of the cortical command, was bilaterally increased despite ve ry asymmetric clinical status, When the duration of the disease was mo re than 36 months, EMG depression returned to its control level. No co rrelation was found between the amount of the EMG depression and parki nsonian symptoms before and after levodopa treatment. Conclusion-Incre ase of the relative ''non-monosynaptic'' part of the cortical command could reflect a compensatory mater mechanism elaborated upstream from the motor cortex.