Gascho, D. | Search bioRxiv

bioRxiv2026

Sleep-dependent modulation of thalamic brain temperature estimates in humans

Mammalian thermal physiology is geared towards dissipating heat during sleep. Brain temperature typically decreases during non-rapid-eye-movement (NREM) sleep in all mammalian species measured to date, yet non-invasive confirmation in healthy humans is lacking: the only available human study used invasive recordings in epileptic patients without a wake control condition. Magnetic resonance spectroscopy (MRS) enables brain temperature mapping non-invasively, using the temperature-sensitive chemical shift of water relative to N-Acetyl-Aspartate as an internal reference. First, we validated that with metabolite cycling (MC), a MRS approach that enables the simultaneous acquisition of metabolite and water information without conventional water suppression, can be used to determine estimates of brain temperature in an ex vivo sheep head. Next, we determined that by using a temporal resolution of ~4 minutes, we obtained high-quality spectra without losing excessive temporal resolution. We then re-analyzed an existing set of MRS data (acquired with the MC sequence) of the thalamus in young adults (n=9) who slept in the evening for up to 2 hours in the scanner, to assess sleep-evoked changes in estimates of brain temperature. Of the nine participants, five participants took part in the subsequent wake-only experiment, allowing to control for the potential impact of circadian time and body posture on estimates of brain temperature. Sleep-wake states were quantified with standard polysomnography, confirming that the participants managed to sleep in the scanner. On average, they spent 39.4+/-15.7 min in N2 sleep, 24.8+/-18.1 min in N3 sleep, 10.0+/-4.9 min in N1 sleep, and 37.0+/-19.6 min awake. Estimates of brain temperature were correlated across the sleep and wake-only experiment within the same participant (R^2=0.29, P<0.0001). When participants entered NREM sleep, estimates of brain temperature decreased by 0.2 degrees Celcius. Moreover, the deeper NREM sleep, the more pronounced the decrease in estimates of brain temperature (P=0.014). These data suggest that an evening nap consisting of NREM sleep decreases thalamic temperature. Considering the profound impact temperature can have on brain functioning, these brain temperature changes could be a pathway through which sleep impacts the brain.

neuroscience↗

bioRxiv2019

Pseudolesion in the right parafissural liver parenchyma on CT: the base is found in embryology and collagen content.

BackgroundComputed tomography (CT) images of livers may show a hypo-attenuated structure alongside the falciform ligament, which can be a focal fatty pseudolesion and can mimic a malignancy. The preferred location is on the right parafissural site, ventral in segment IVa/b. The etiology is not clear, nor is it known how the histology of this location develops. These are evaluated in this study.\n\nMethods40 adult cadavers with autopsy and / or postmortem CT in a university hospital and a forensic center were included. Liver biopsies were taken at the left side of the falciform ligament as control, and at the right side as the possible precursor of a pseudolesion; these were examined for collagen and fat content. Cadavers with steatotic (>5% fat) or fibrotic (>2% collagen) control samples were excluded.\n\nResultsSignificantly more collagen was present in the right parafissural liver parenchyma: median 0.68% (IQR: 0.32 - 1.17%), compared to the left side 0.48% (IQR: 0.21 - 0.75%) (p 0.008), with equal fat content and CT attenuation values. The etiophysiology goes back to the demise of the umbilical venes in the early embryonic and neonatal period.\n\nConclusionsThe right parafissural area contains more collagen and an equal amount of fat compared to the control left side. This supports the hypothesis of delayed, third inflow: the postnatal change in blood supply from umbilical to portal leaves the downstream parafissural area hypoperfused leading to hypoxia which in turn results in collagen accumulation and the persistence of paraumbilical veins of Sappey.\n\nKey pointsO_LIThe typical location for a parafissural hepatic pseudolesion contains increased collagen.\nC_LIO_LIA change in histology is caused by physiological demise of the umbilical venes.\nC_LIO_LIThe suboptimal blood supply of the right parafissural side leads to hypoxia and collagen deposition.\nC_LIO_LIEmbryologic knowledge and postmortem histology can help resolve issues in radiology.\nC_LI

physiology↗