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

B-U Kleine, Peter Praamstra, DF Stegeman, MJ Zwarts

Research output: Contribution to journalArticle

48 Citations (Scopus)


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.
Original languageEnglish
Pages (from-to)477-483
Number of pages7
JournalExperimental Brain Research
Publication statusPublished - 1 Jun 2001


  • transcranial magnetic stimulation
  • Parkinson's disease
  • motor unit firing
  • cortical excitability
  • high-density surface electromyography


Dive into the research topics of 'Impaired motor cortical inhibition in Parkinson's disease: Motor unit responses to transcranial magnetic stimulation'. Together they form a unique fingerprint.

Cite this