ABSTRACT: Background and Aims. The motor-evoked potential (MEP) to transcranial magnetic stimulation (TMS), its recruitment and the conditioning effects of weak stimuli in Parkinson’s disease (PD) have shown contradictory results based on limited use and analysis of existing TMS paradigms. We undertook this study to provide definitive data of MEP physiology in PD.
Methods. We investigated resting and active motor thresholds (RMT/AMT), resting and active
recruitment curves, and short-interval intracortical inhibition (ICI) and facilitation (ICF) in 39
PD patients and 40 healthy individuals. MEP was log transformed prior to analysis. The Unified
Parkinson’s Disease Rating Scale (UPDRS) motor scale was used as clinical measure.
Results. MEPs to single pulses were slightly, but significantly, larger in the patients at
rest, but increased much less with voluntary muscle activation. PD patients also showed
clearly and consistently less ICI and ICF by the conditioning pulse. Both facilitation and
inhibition correlated with MEP threshold in healthy subjects, but not in patients. No phys-
iological measures correlated with the UPDRS score.
Conclusions. These findings are compatible with a decreased evoked and spontaneous
thalamocortical drive by disturbed signal-noise ratio of pyramidal neuron responses to
unbalanced excitatory/inhibitory input. More importantly, they probably represent
a complex combination of disturbed presynaptic and surround inhibition, as consequence
of aberrant oscillatory neural transmission due to dysfunctional neurotransmitter
Archives of Medical Research 01/2012; N/A(N/A-N/A):N/A. · 1.88 Impact Factor