Key pointsr Sleep spindle frequency positively, duration negatively correlates with brain temperature. r Local heating of the thalamus produces similar effects in the heated area. r Thalamic network model corroborates temperature dependence of sleep spindle frequency. r Brain temperature shows spontaneous microfluctuations during both anesthesia and natural sleep.r Larger fluctuations are associated with epochs of REM sleep. r Smaller fluctuations correspond to the alteration of spindling and delta epochs of infra-slow oscillation.Abstract Every form of neural activity depends on temperature, yet its relationship to brain rhythms is poorly understood. In this work we examined how sleep spindles are influenced by changing brain temperatures and how brain temperature is influenced by sleep oscillations. We employed a novel thermoelectrode designed for measuring temperature while recording neural activity. We found that spindle frequency is positively correlated and duration negatively correlated with brain temperature. Local heating of the thalamus replicated the temperature dependence of spindle parameters in the heated area only, suggesting biophysical rather than global modulatory mechanisms, a finding also supported by a thalamic network model. Finally, Marton Csernai is a postdoctoral researcher with a background in electrical engineering and computer science. His primary research focuses on the network effects of sleep processes, especially how cell ensembles behave during sleep spindles. M. Csernai, S. Borbély and K. Kocsis contributed equally to this work.This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. 4070M. Csernai and others J Physiol 597.15 we show that switches between oscillatory states also influence brain temperature on a shorter and smaller scale. Epochs of paradoxical sleep as well as the infra-slow oscillation were associated with brain temperature fluctuations below 0.2°C. Our results highlight that brain temperature is massively intertwined with sleep oscillations on various time scales.

The proposed multifunctional tool is envisioned to broaden our knowledge on the role of the thermal modulation of neuronal activity in both cortical and deeper brain regions.

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