Figure 1. Following MPTP treatment, the circadian locomotor rest-activity rhythm is abolished under constant light.

(A) Pre-MPTP treatment, daily locomotor activity is synchronized to the LD cycle (dark phase shown by shading) and in constant light (LL) the circadian rhythm free runs with a period of 23.97 hrs (Monkey Y). (B) Same animal, 4.8 months post-MPTP treatment, rest-wake activity is synchronized to the LD cycle but becomes arrhythmic in LL. Compared to pre-treatment, periodogram analyses (panels to right of actograms) confirm a quantitative decrease in amplitude during LD and the absence of rhythmicity during LL. The averaged 24 h locomotor activity profiles (C–D) illustrate the consolidated activity during the light phase in LD cycle both pre- and post-MPTP and during LL pre-MPTP but a complete loss of rhythmicity post-MPTP.