Nonvisual responses to light exposure in the human brain during the circadian night.
The brain processes light information to visually represent the environment but also to detect changes in ambient light level. The latter information induces non-image-forming responses and exerts powerful effects on physiology such as synchronization of the circadian clock and suppression of melatonin. In rodents, irradiance information is transduced from a discrete subset of photosensitive retinal ganglion cells via the retinohypothalamic tract to various hypothalamic and brainstem regulatory structures including the hypothalamic suprachiasmatic nuclei, the master circadian pacemaker. In humans, light also acutely modulates alertness, but the cerebral correlates of this effect are unknown. We assessed regional cerebral blood flow in 13 subjects attending to auditory and visual stimuli in near darkness following light exposures (>8000 lux) of different durations (0.5, 17, 16.5, and 0 min) during the biological night. The bright broadband polychromatic light suppressed melatonin and enhanced alertness. Functional imaging revealed that a large-scale occipito-parietal attention network, including the right intraparietal sulcus, was more active in proportion to the duration of light exposures preceding the scans. Activity in the hypothalamus decreased in proportion to previous illumination. These findings have important implications for understanding the effects of light on human behavior.
Perrin
Fabien
F
Centre de Recherches du Cyclotron (B30), Université de Liège, Sart Tilman, 4000 Liège, Belgium.
Peigneux
Philippe
P
Fuchs
Sonia
S
Verhaeghe
Stéphane
S
Laureys
Steven
S
Middleton
Benita
B
Degueldre
Christian
C
Del Fiore
Guy
G
Vandewalle
Gilles
G
Balteau
Evelyne
E
Poirrier
Robert
R
Moreau
Vincent
V
Luxen
André
A
Maquet
Pierre
P
Dijk
Derk-Jan
DJ
D000161:Acoustic Stimulation; D000328:Adult; D000704:Analysis of Variance; D001288:Attention / Q000502:physiology* / Q000528:radiation effects; D001921:Brain / Q000098:blood supply* / Q000378:metabolism; D006801:Humans; D008027:Light; D008279:Magnetic Resonance Imaging; D008550:Melatonin / Q000097:blood*; D010775:Photic Stimulation; D049268:Positron-Emission Tomography; D012039:Regional Blood Flow / Q000502:physiology / Q000528:radiation effects
D008550:Melatonin