Electrically stimulating a nerve in the face has shown promise for boosting memory. Bursts of stimulation, delivered via skin electrodes, appear to improve signalling between cells in the hippocampus, a brain region crucial for memory. In a small study, this then enabled people to better remember what a group of strangers did for a living.
What is a ‘normal’ memory slowdown, and when should I worry? Electrical stimulation has been linked to improved memory before, but this is usually highly invasive or requires people to lie in a scanner. In 2024, Myles McLaughlin at the Leuven Brain Institute in Belgium and his colleagues showed that a non-invasive technique, called transcranial direct current stimulation, sparks the trigeminal nerve – a three-part nerve in the head that carries sensory information between parts of the face and the brain.
This then activated a pathway leading to the hippocampus. Now, the researchers have set out to understand whether this affects memory. They first established the best type of stimulation to apply, by delivering electrical stimulation to the trigeminal nerve of anaesthetised rats, via small electrodes under the skin.
They found that 1-second bursts of 200-hertz electrical stimulation, separated by 29 seconds of rest, increased signalling between hippocampal neurons by about 20 per cent. This continued for at least 90 minutes after the stimulation ended. In contrast, continuous stimulation at 100 hertz had no effect.
The researchers think intermittent stimulation specifically activates the locus coeruleus, a blue blob of neurons measuring just a few millimetres. This is the brain’s primary producer of noradrenaline, or norepinephrine – a chemical messenger that helps transmit nerve signals between neurons, and may also enhance memory. When the researchers repeated the intermittent stimulation, but this time with the locus coeruleus chemically suppressed, they found there was no lasting increase in hippocampal activity.
Next, the researchers studied nine people with drug-resistant epilepsy who had electrodes implanted in their brains for routine monitoring. Skin electrodes around their jaw delivered the same pattern of 200-hertz stimulation to the trigeminal nerve for 20 minutes. This produced a similar electrical response in the hippocampus as that observed in the rats.
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