DAYTIME DETERIORATION OF INHIBITORY CONTROL IN LEVODOPA-INDUCED DYSKINESIA: EVIDENCE FROM GO/NOGO ERP

Levodopa-induced dyskinesia (LID) in Parkinson's disease (PD) involves dysregulated dopaminergic plasticity that impairs inhibitory control, potentially leading to speed-accuracy trade-offs in Go/NoGo tasks during levodopa ON states. Synaptic homeostasis theory posits that wakefulness promotes synaptic upscaling, while sleep downscales efficacy to restore network capacity; disruptions in LID may heighten daytime vulnerability. This study examined whether LID patients, tested on the same day in ON state, exhibit (i) evening declines in Go/NoGo performance and (ii) reduced central P3 discrimination between GO and NOGO conditions. Controls (CTL, n=10) and PD subgroups, i.e., early PD (EPD, n=7), advanced non-dyskinesic (ADV, n=8), dyskinesic (DYS, n=7), completed a Go/NoGo task in morning (m1) and evening (s1) sessions under ON conditions. We quantified GO accuracy and NOGO error rate. Event-related potentials (ERPs) at Cz focused on P3 peak (250-450 ms) for GO versus NOGO trials, using Shapiro–Wilk normality testing to select paired t-tests or Wilcoxon signed-rank tests within groups, and ANOVA across groups, with correction for multiple comparisons.The DYS group showed significant GO accuracy decline (p<0.05) and NOGO error increase (p<0.05) from m1 to s1, unlike other groups. P3 GO-NOGO differences were evident across all groups/sessions except DYS s1 (non-significant), indicating evening loss of electrophysiological discrimination despite preserved morning responses.These findings reveal intra-daily vulnerability in LID inhibitory control, marked by behavioral/ERP deterioration. These data are compatible with a progressive loss of network selectivity/efficiency throughout the day and eventually linked with impaired homeostatic synaptic regulation during wakefulness. Intra-daily timing merits consideration in LID neurophysiology studies.