Zapping sleepers’ brains boosts memory

Roxanne Khamsi

Applying a gentle electric current to the brain during sleep can significantly boost memory, researchers report.

A small new study showed that half an hour of this brain stimulation improved students’ performance at a verbal memory task by about 8%. The approach enhances memory by creating a form of electrical current in the brain seen in deep sleep, the researchers suggest.

Jan Born at the University of Luebeck in Germany, and colleagues, recruited 13 healthy medical students for the study and gave them a list of word associations, such as “bird” and “air”, to learn late in the evening. Afterwards, researchers placed two electrodes on the forehead and one behind each ear of the volunteers and let them sleep.

The students’ various sleep stages were monitored using an electroencephalogram (EEG) machine. When the students entered a period of light sleep, Born’s team started to apply a gentle current in one-second-long pulses, every second, for about 30 minutes. The EEG readings revealed that this current had put students into a deeper state of sleep.

The next morning, the students performed about 8% better on the word memory test than when they underwent the same type of memory experiment without brain stimulation.

Nerve firing

Born believes this memory boost was due to the pattern of the applied current mimicking that seen in naturally occurring deep sleep, where memory consolidation is thought to take place.

Strong brain currents in this stage of sleep probably cause more intense nerve firing, he says, which might enhance activity in the brain’s memory centre, the hippocampus.

Some researchers are sceptical of Born's "mimicking deep sleep" theory, however. Felipe Fregni at the Harvard Center for Non-invasive Brain Stimulation in Boston, US, says that he and other scientists have shown that brain stimulation with non-sleep-type currents can produce similar memory enhancements.

Potential side effects

There is growing evidence that brain stimulation might one day help improve memory in patients with dementia or other forms of cognitive impairment, experts say.

“It could be very useful to restore function in people with brain injury,” says Daniel Herrera at Weill Medical College of Cornell University in New York, US, who has studied the effects of brain stimulation in rats.

Healthy people might eventually try using this approach to maximise their brainpower, Herrera says: “I think every single medical student in the country might want to plug into this type of device at home or in the dorm.” But he stresses that applying electrical currents to the brain might have unwanted side effects.

Born also says he would be "a little hesitant” to regularly use brain stimulation during sleep to boost memory: “In the end we don’t know if there are adverse side effects that we just don’t recognise at the moment.”

Journal reference: Nature (DOI: 10.1038/nature05278)

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