We're all familiar with the feeling of zoning out, especially when we're sleep-deprived . A new study suggests these brief wanderings of attention are our brain's attempts to catch up on maintenance that usually happens while we snooze.

The study, from researchers at the Massachusetts Institute of Technology (MIT), used brain measurements taken by both electroencephalogram (EEG) caps and functional magnetic resonance imaging (fMRI) scanners.

Periods of zoning out – or "attentional failures", in the words of the study – were accompanied by a wave of cerebrospinal fluid (CSF) flowing out of the brain, before it returned a second or two later.

The patterns matched the waves of CSF that usually happen during deep sleep . The thinking is that this nightly fluid flow helps wash away w

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