title: Activation of suprachiasmatic nuclei and primary visual cortex depends upon time of day.
abstract: The human suprachiasmatic nucleus (SCN), the master biological clock, is a small (approximately 2 mm(3)) and deep structure located in the anterior hypothalamus. Previous methods do not allow in vivo study of the human SCN in a non-invasive manner. Therefore, we explored blood oxygen level-dependent (BOLD)-functional magnetic resonance imaging (fMRI) with OFF-ON-OFF block-designed visual stimuli to record the activities in the 'SCN and peri SCN in the anterior hypothalamus' (SCN+) and the primary visual area V1 using a 3T Siemens scanner and six normal subjects. We found that: (i) the BOLD-fMRI response to light and the mean of percentage activation in the SCN+ at midday was significantly less than that at night; and (ii) the number of activated voxels in most of the visual area V1 at midday was significantly higher than that at night. We conclude that BOLD-fMRI responses to light in the SCN+ and the V1 areas vary with time of day. This conclusion is consistent with: (i) the previously measured phase-response curve to light [J. Physiol., 549.3 (2003) 945] for the SCN activity at critical intensity threshold; and (ii) the interaction of the melanopsin-based signals with the rod-cone signals at the 'giant' retinal ganglion cells [Nature, 433 (2005) 749] for the V1 activity.
authors.affiliation: Brain Imaging Center, McLean Hospital, Belmont, MA, USA. rlpvimal@yahoo.co.in
authors.forename: Ram L P
authors.initials: RL
authors.lastname: Vimal
authors.forename: Manju-Uma C
authors.initials: MU
authors.lastname: Pandey-Vimal
authors.forename: Love-Shyam P
authors.initials: LS
authors.lastname: Vimal
authors.forename: Blaise B
authors.initials: BB
authors.lastname: Frederick
authors.forename: Edward G
authors.initials: EG
authors.lastname: Stopa
authors.forename: Perry F
authors.initials: PF
authors.lastname: Renshaw
authors.forename: Shalini P
authors.initials: SP
authors.lastname: Vimal
authors.forename: David G
authors.initials: DG
authors.lastname: Harper
mesh_terms: D000328:Adult; D001683:Biological Clocks / Q000502:physiology; D001931:Brain Mapping; D002940:Circadian Rhythm / Q000502:physiology*; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D010775:Photic Stimulation; D012160:Retina / Q000166:cytology / Q000502:physiology*; D012165:Retinal Ganglion Cells / Q000502:physiology; D017299:Rod Opsins / Q000502:physiology; D012684:Sensory Thresholds / Q000502:physiology; D013493:Suprachiasmatic Nucleus / Q000166:cytology / Q000502:physiology*; D013997:Time Factors; D014785:Vision, Ocular / Q000502:physiology; D014793:Visual Cortex / Q000166:cytology / Q000502:physiology*; D014795:Visual Pathways / Q000166:cytology / Q000502:physiology*; D055815:Young Adult; D000099210:Melanopsin
chemical_list: D017299:Rod Opsins; D000099210:Melanopsin