One bad night made people less willing to help

Researchers at the University of California, Berkeley tested whether sleep loss changes willingness to help others at three different scales: inside individual brains using fMRI, across ordinary days using sleep diaries, and across an entire society using a dataset of more than three million charitable donations.

After one night of total sleep deprivation, participants reported less willingness to help and showed reduced activity in brain regions tied to understanding others' needs. People who slept worse on an ordinary night wanted to help less the next day, and donations dropped after clocks moved forward for daylight saving, when sleep is briefly cut by about an hour.

The same pattern held at every scale tested, from a single brain scan to daily sleep diaries to millions of donation records, strengthening the case that sleep loss itself was driving the drop in prosocial behavior. The societal data relied on a natural, unplanned sleep disruption rather than a controlled experiment, so other factors that week cannot be entirely excluded, though the pattern matched the lab findings closely.

Lost sleep made people measurably less generous.