Everybody loses a night of sleep sometimes — on campus, especially during exams. According to Nora D. Volkow, who gave a talk at Radcliffe’s Knafel Center Thursday titled “The Sleep-Deprived Human Brain,” a single sleepless night is probably harmless. But the cumulative effects of sleep deprivation may be more dangerous than is currently understood.

Volkow, now the director of the National Institute on Drug Abuse at the National Institutes of Health, was a pioneer in positron emission tomography (PET) brain imaging, and helped carry out early studies confirming the toxic effects of cocaine. At Harvard, she reported on two sets of brain-imaging studies that shed light on the way sleep deprivation interferes with cognition, as well as its possible links to dementia and Alzheimer’s disease.

Her work in drug research, she said, led to an investigation of sleep patterns. One toxic property of cocaine is that it interferes with sleep.

“If you give cocaine to an animal, it is the only drug that will cause it to forgo sleep, and the animals ultimately died because they did not survive this,” she said. Yet lack of sleep itself produces some of the same adverse effects that drugs do: It disrupts memory, inhibits alertness, and can contribute to obesity.

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“It also results in accidents, and there are more fatalities associated with improper sleep behavior than there are with alcohol,” said Volkow, whose presentation was a 2017–2018 Kim and Judy Davis Dean’s Lecture in the Sciences..

Volkow’s work included a look at the effects of sleep deprivation on the dopamine system, which regulates alertness and overall brain function. After running magnetic resonance imaging and PET scans on sleep-deprived human subjects, she found that lack of sleep inhibited certain parts of dopamine transmission: Brain cells were able to release dopamine, but not to receive it.

“The decrease in dopamine receptors can be likened to going to an auditorium when nobody is there,” she said.

Changes linked to sleep deprivation didn’t necessarily create tiredness, but could potentially lead to more dangerous conditions.

“When people are sleep-deprived they are less likely to regulate their desires, and they engage in impulsive behaviors,” Volkow said.