van Osch, M. J. P. | Search bioRxiv

bioRxiv2023

Preliminary cross-sectional investigations into the human glymphatic system using multiple novel non-contrast MRI methods.

We discuss two potential non-invasive MRI methods to cross-sectionally study two distinct facets of the glymphatic system and its association with sleep and aging. We apply diffusion-based intravoxel incoherent motion (IVIM) imaging to evaluate pseudodiffusion coefficient, D*, or cerebrospinal fluid (CSF) movement across large spaces like the subarachnoid space (SAS). We also performed perfusion-based multi-echo, Hadamard encoded multi-delay arterial spin labeling (ASL) to evaluate whole brain cortical cerebral blood flow (CBF) and transendothelial exchange (Tex) of water from the vasculature into the perivascular space and parenchyma. Both methods were used in young adults (N=9, 6F, 23{+/-}3 years old) in the setting of sleep and sleep deprivation. To study aging, 10 older adults, (6F, 67{+/-}3 years old) were imaged after a night of normal sleep only and compared with the young adults. D* in SAS was significantly (p<0.05) lesser after sleep deprivation (0.014{+/-}0.001 mm2/s) than after normal sleep (0.016{+/-}0.001 mm2/s), but was unchanged with aging. Cortical CBF and Tex on the other hand, were unchanged after sleep deprivation but were significantly lower in older adults (37{+/-}3 ml/100g/min, 476{+/-}66 ms) than young adults (42{+/-}2 ml/100g/min, 624{+/-}66 ms). IVIM was thus, sensitive to sleep physiology and multi-echo, multi-delay ASL was sensitive to aging.

neuroscience↗

bioRxiv2021

The photobiology of the human circadian clock

In modern society, the widespread use of artificial light at night disrupts the suprachiasmatic nucleus (SCN), which serves as our central circadian clock. Existing models describe excitatory responses of the SCN to primarily blue light, but direct measures in humans are absent. The combination of state-of-the-art neuroimaging techniques and custom-made MRI compatible LED devices allowed to directly measure the light response of the SCN. In contrast to the general expectation, we found that SCN activity was suppressed by light. The suppressions were observed not only in response to narrowband blue light ({lambda}max: 470nm) but remarkably, also in response to green ({lambda}max: 515nm) and orange ({lambda}max: 590nm), but not to violet light ({lambda}max: 405nm). The broadband sensitivity of the SCN implies that strategies on light exposure should be revised: enhancement of light levels during daytime is possible with wavelengths other than blue, while during nighttime, all colors are potentially disruptive.

neuroscience↗