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Struggling to remember something? An electrical jolt deep in the brain might help – if it is given at the right time.

To discover the effect of electrical stimulation on memory, and colleagues at the University of Pennsylvania turned to 150 volunteers who had previously had electrodes implanted in their brains to help control severe epilepsy. These electrodes can record the brain’s electrical signals, giving the team a window into each person’s neural processes. They can also deliver electricity to the brain.

First, the team recorded the brain signals of the volunteers while they learned items from a list, and later as they tried to recall those items. They then applied machine learning methods to this brain signal data, enabling them to predict if a person’s efforts to commit something to memory would later prove successful, based on the state of their brain at the time.

The team next ran further recall tests, during which they delivered random jolts of electricity to the participants while they were trying to memorise test items. They compared the effects of jolting someone during two different brain states – the pattern of signals linked to being likely to later remember something, and the pattern linked to being more likely to have a memory lapse.

They found that giving electrical stimulation when a person’s brain signals suggested they would later forget the current item made that person 13 per cent more likely to recall it. “You get significant enhancement,” says Kahana.

Timing was key, however. A jolt of electricity during a pattern of brain activity linked to later recall went on to reduce a person’s likelihood of remembering an item by 18 per cent.

Memory device

The study is the latest of many probing the question of whether zaps of electricity can improve memory. So far, many studies have conflicted with each other on the effects of deep brain stimulation and recall. “Electrical brain stimulation is controversial,” says at Imperial College London. “The majority of studies have a very low number of participants. A study of this size is much more reliable.”

Kahana is now working on a device that could tell when the brain would benefit from an induced memory boost. “You could build a technology that could trigger stimulation at moments when you’re predicted to have poor memory, thus enhancing memory of an individual wearing such a device,” says Kahana.

Such a device may be useful for people who have memory loss, but first we need to understand which parts of the brain benefit the most from this kind of stimulation.

While deep brain stimulation already helps people with untreatable epilepsy or Parkinson’s disease, it’s an extreme treatment that carries the risk of infection. Experimental approaches that stimulate the brain externally may be a more desirable option.

Read more: Alzheimer’s damage reversed by deep brain stimulation; Deep brain stimulation: A wonder treatment pushed too far?