Daily time-course of frontal SEPs: Relation to L-dopa plasma levels and motor performance in PD patients

Objective: To verify whether the change in L-dopa plasma levels after a single dose of controlled release carbidopa/levodopa 50/200 transiently modifies frontal components of somatosensory evoked potentials (SEPs) in patients with Parkinson's disease (PD), in parallel with improvement of motor performance. Background: Apomorphine, a potent dopamine agonist drug, is able to transiently increase frontal SEP components, which may be depressed in PD; however, relationships between clinical status, frontal SEPs and therapy are still unclear. Design/methods: Nineteen PD patients (mean age 65.9 years; range 52-77 years), responders to therapy, were studied in the same day at times TO (baseline predose level), Tl (presumed L-dopa peak time) and T2 (end of dose-induced motor response). The following parameters were monitored at each time: L-dopa plasma concentration, tapping test, reaction times, peak latency (with central conduction times) and amplitude of cervical, subcortical, as well as cortical parietal and frontal SEP components elicited by median nerve stimulation of the more clinically effected arm. Results: On average, the amplitude of frontal SEPs was significantly reduced at TO vs. control subjects. A significant and transient amplitude increase of frontal SEPs was found at Tl, in parallel with the L-dopa peak concentration and and improvement in motor performance, without significant changes of partictal SEP waves. No latency shifts were observed. Conclusions: L-dopa may influence the responsiveness of the parkinsonian brain as expressed by frontal SEPs. The time-course of these modifications coincides with that of the clinical response in the motor performance.