Time course of frontal somatosensory evoked potentials - Relation to L-dopa plasma levels and motor performance in PD

Objective: To verify whether the change in L-dopa plasma levels after a sin gle dose of carbidopa/L-dopa 50/200 (controlled-release) transiently modifi es frontal components of somatosensory evoked potentials (SEPs) in patients with PD in parallel with improvement of motor performance. Background: Apo morphine, a potent dopamine-agonist drug, transiently increases frontal SEP components, which may be depressed in PD; however, relationships between c linical status, frontal SEPs, and therapy are still unclear. Methods: Ninet een PD patients (mean age 65.9 years, range 52 to 77, responders to L-dopa therapy, were studied in the same day at times TO (baseline predose level), T1 (presumed L-dopa peak time), and T2 tend of dose-induced motor response ). The following were monitored: L-dopa plasma concentration, tapping test, reaction times, peak latency (with central conduction times), and amplitud e of cervical, subcortical, as well as cortical parietal and frontal SEP co mponents elicited by median nerve stimulation of the more clinically affect ed arm. Results: The average amplitude of frontal components of PD patients was significantly reduced at TO with respect to control subjects. A signif icant and transient amplitude increase of frontal SEPs was found at T1, in parallel with the L-dopa peak concentration and improvement in motor perfor mance (tapping and reaction times), without significant changes in amplitud e of parietal SEP waves. No latency shifts were observed in brain and spina l waves. Conclusions: L-Dopa may influence the responsiveness of the parkin sonian brain as assessed by frontal somatosensory evoked potentials. The ti me course of these modifications coincides with that of the clinical respon se in the motor performance.