Diurnal variation of brain activity in the human suprachiasmatic nucleus

Abstract

The suprachiasmatic nucleus (SCN) is the central clock for circadian rhythms. Animal studies have revealed daily rhythms in the neuronal activity in the SCN. However, the circadian activity of the human SCN has remained elusive. In this study, to reveal the diurnal variation of the SCN activity in humans, the SCN was localized, and its activity was investigated using perfusion imaging. We scanned each participant four times a day, every six hours, and higher activity was observed at noon while lower activity was recorded in the early morning. The SCN activity was then measured every thirty minutes for six hours from midnight to dawn and showed a decreasing trend and was comparable with the rodent SCN activity after switching off the lights. These results suggest that the diurnal variation of the human SCN follows the zeitgeber cycles of mammals and is modulated by physical lights rather than the local time.

Hypertension: Causes and Consequences of Circadian Rhythms in Blood Pressure

“…242 Other data support this possibility. 241 While these findings are thought provoking, the methodology used to image this small nuclei has been criticized, 243 emphasizing that additional work on th regulation of CBF to the SCN is needed. Rapid changes in eNOS expression have been seen during severe hypoxia within SCN endothelial cells, consistent with a potential influence of eNOS on local CBF.…”

“…Based on changes in local blood flow, activity of the human SCN was the highest at noon and the lowest at 06:00 hours. 241 In humans using blood O 2 level–dependent functional magnetic resonance imaging, exposure to several colors of light caused a reduction (not activation) in the blood O 2 level–dependent signal, suggesting reversed neurovascular coupling within the SCN. 242 Other data support this possibility.…”