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Kristin Koller, Paul Mullins, Robert Rafal; Diffusion Tensor Imaging Tractography Of Circadian Regulating Circuits In The Human Brain. Journal of Vision 2014;14(10):987. doi: 10.1167/14.10.987.
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© ARVO (1962-2015); The Authors (2016-present)
Circadian rhythms are endocrinological, physiological and behavioural rhythms that oscillate with a period close to 24 hours by precise orchestration of external environmental cues and internal neuro-endocrine circuits. By example, the rhythm of sleep is influenced by an external time-cue (light from the sun). Photosensitive melanopsin containing retinal ganglion cells transmit light signals through the inferior accessory optic tract to an internal pacemaker in the suprachiasmatic nucleus of the hypothalamus. The projection connects to sympathetic nerve fibres through the intermedio-lateral column of the spinal cord. From the spinal cord, sympathetic nerves innervate the pineal gland, via the superior cervical sympathetic ganglion, thereby stimulating secretion of the sleep inducing hormone melatonin. While the anatomy of this circuitry has been demonstrated by tracer studies in rats, a human anatomical homologue circuit remains to be established. Here we report results from virtual white matter dissections in nine humans, using probabilistic diffusion tensor imaging tractography. The dissection was achieved using a seed mask in the optic chiasm and waypoint masks in the periaqueductal region and the lateral medulla (through which projection from the hypothalamus to the sympathetics are known to traverse in humans.) The observed streamlines are consistent with the topography of circadian projections from the hypothalamus in the rat. Furthermore, the extent to which individuals reported to have 'early bird' sleep traits correlated with high mean fractional anisotropy (a measure of connectivity strength) of the streamline. Correlation findings reported here support the functional authenticity of our virtual dissections, and suggest that 'early bird' or 'night owl' chronotypes may be predisposed traits of hard-wired circuits in humans. Keywords: circadian rhythms, diffusion tensor imaging, hypothalamus, pineal gland, suprachiasmatic nucleus, sympathetics
Meeting abstract presented at VSS 2014
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