What it is
Nearly all the blood supplying the cortex leaves through bridging veins that drain into the superior sagittal sinus. Using optical imaging in head-fixed mice, the authors found that these veins and the sinus constrict in under a tenth of a second at the onset of locomotion, after whisker stimulation and on waking from sleep, and that the constrictions track abdominal muscle activity and, at rest, breathing. Applying pressure to the abdomen of anaesthetized mice produced constrictions of the same size and timing, along with a rapid but transient increase in blood flow.
Why it matters
The diameters of the brain's smaller surface and internal vessels are largely controlled by local signals, but these large draining veins turn out to be regulated during behavior partly by the abdominal muscles acting on intracranial pressure, a mechanical link between the central nervous system and the viscera. The finding also matters for methods: the rapid drop in blood volume produced spurious increases in fluorescence in mice expressing fluorescent reporters, artifacts that can mimic functional brain signals.
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Filed underCerebrospinal fluid and hydrocephalus, Barrier Structure and Function Studies, Neuroscience of respiration and sleep