Impaired motor cortical inhibition in Parkinson's disease : Motor unit responses to transcranial magnetic stimulation

• Published in: Experimental brain research Vol. 138; no. 4; pp. 477 - 483
• Main Authors: KLEINE, Bert U, PRAAMSTRA, Peter, STEGEMAN, Dick F, ZWARTS, Machiel J
• Format: Journal Article
• Language: English
• Published: Berlin Springer 01.06.2001; Springer Nature B.V
• Subjects: Action Potentials - physiology; Aged; Amyotrophic lateral sclerosis; Biological and medical sciences; Cortex (motor); Degenerative and inherited degenerative diseases of the nervous system. Leukodystrophies. Prion diseases; Elbow; Electric Stimulation; Electromyography; Excitability; Excitatory Postsynaptic Potentials - physiology; Female; Firing pattern; Humans; Magnetic fields; Male; Medical sciences; Membrane potential; Middle Aged; Motor Cortex - physiopathology; Motor neuron diseases; Motor Neurons - physiology; Motor units; Movement disorders; Muscle Contraction - physiology; Muscle, Skeletal - innervation; Muscle, Skeletal - physiopathology; Neural Inhibition - physiology; Neurodegenerative diseases; Neurology; Parkinson Disease - physiopathology; Parkinson's disease; Pyramidal tracts; Pyramidal Tracts - physiopathology; Reaction Time - physiology; Synaptic Transmission - physiology; Transcranial Magnetic Stimulation; Human; Nervous system diseases; Discharge pattern; Excitability; Parkinson disease; Corticospinal bundle; Motor neuron; Striated muscle; Motor control; Motor unit; Cerebral disorder; Electrodiagnosis; Pyramidal motor pathway; Motor cortex; Central nervous system disease; Magnetic stimulus; Degenerative disease; Electromyography; Extrapyramidal syndrome
• ISSN: 0014-4819; 1432-1106
• DOI: 10.1007/s002210100731

Transcranial magnetic stimulation (TMS)-induced corticospinal volleys can be investigated in detail by analysing the firing pattern modulation of active motor units (MUs) at close to threshold stimulation strengths. In amyotropic lateral sclerosis (ALS) these volleys are dispersed and prolonged, attributed to altered motor cortical excitability. Impaired intracortical inhibition, as found in ALS, is not unique to this disease, but is also a well-established finding in Parkinson's disease (PD). The present study explored whether reduced inhibition in the motor cortex in PD is accompanied by similar changes in motor unit firing modulation by TMS as are found in ALS. TMS was applied to the contralateral motor cortex during a low-force voluntary elbow flexion while 126-channel surface electromyography (SEMG) was recorded from the brachial biceps muscle. A recently developed method for SEMG decomposition was used to extract the firing pattern of up to five simultaneously active MUs. Sixteen MUs in 7 PD patients and 17 MUs in 5 healthy control subjects were analysed and peristimulus time histograms (PSTHs) and interspike interval change functions (IICFs) were calculated. The IICF provides an estimate of the modulation of the postsynaptic membrane potential at the spinal motoneuron, evoked by the stimulus. In PD the duration of the PSTH peak was significantly increased and the synchrony was decreased. The excitatory phase at 20-50 ms of the IICF was broader in PD, reflecting a longer duration of the TMS-evoked excitatory postsynaptic potential. It is proposed that these results are due to prolonged corticospinal volleys resulting from impaired intracortical inhibition.