The aging human brain exhibits reduced hemodynamic and cerebrospinal fluid flow waves during sleep.

Reduced sleep-dependent cerebrospinal fluid flow waves in older adults (60–84 years) are linked to diminished EEG slow wave power, lower global hemodynamic oscillations, and gray matter atrophy.

• Why it matters: Aging is associated with poorer sleep, and sleep disruption predicts later neurodegeneration and cognitive decline, potentially via altered CSF circulation needed for brain homeostasis.
• What they did: Large-scale CSF flow and hemodynamics were imaged during nighttime sleep in young adults (18–39 years) and older adults (60–84 years), with sensory and vasoactive stimuli used to probe neural and cerebrovascular contributions.
• The result: Sleep-dependent CSF flow was reduced in older adults, and stimulus-driven tests indicate both neural and cerebrovascular changes contribute, suggesting parallel mechanisms before disease onset.

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