Memory can be boosted by using a magnetic field to stimulate part of the brain, a study has shown. The effect lasts at least 24 hours after the stimulation is given, improving the ability of volunteers to remember words linked to photos of faces.
Scientists believe the discovery could lead to new treatments for loss of memory function caused by ageing, strokes, head injuries and early Alzheimer's disease. Dr Joel Voss, from Northwestern University in Chicago, said: "We show for the first time that you can specifically change memory functions of the brain in adults without surgery or drugs, which have not proven effective.
"This non-invasive stimulation improves the ability to learn new things. It has tremendous potential for treating memory disorders."
The scientists focused on associative memory, the ability to learn and remember relationships between unrelated items. An example of associative memory would be linking someone to a particular restaurant where you both once dined. It involves a network of different brain regions working in concert with a key memory structure called the hippocampus, which has been compared to an "orchestra conductor" directing brain activity. Stimulating the hippocampus caused the "musicians" – the brain regions – to "play" more in time, thereby tightening up their performance.
A total of 16 volunteers aged 21-40 took part in the study, agreeing to undergo 20 minutes of transcranial magnetic stimulation (TMS) every day for five days.
TMS directs a magnetic field at a specific area of the skull to induce weak electrical currents in the brain. It is used to test brain circuits in patients with stroke, multiple sclerosis, motor neurone disease and other conditions, and has been shown to alleviate some forms of depression.
The hippocampus is too deeply embedded in the brain to be stimulated directly by TMS, but the scientists found they could stimulate it indirectly, via a superficial brain region highly connected to the structure that lies a centimetre below the skull surface.
At the start of a series of tests, participants were shown 20 photos of human faces while at the same time hearing words being read aloud. After either undergoing TMS or receiving no stimulation (placebo condition) they were later shown the photos again and asked to recall which words were associated with them.
"They remembered more face-word pairings after the stimulation than before, which means their learning ability improved," Dr Voss said. "That didn't happen for the placebo condition or in another control experiment with additional subjects."
Scans confirmed that the stimulation caused the brain regions to become more synchronised with each other and the hippocampus. Greater improvement in synchronicity or connectivity led to better memory performance.
The results are published in the latest edition of the journal Science.
Dr Voss added: "This opens up a whole new area for treatment studies where we will try to see if we can improve function in people who really need it.
"For a person with brain damage or a memory disorder, those networks are disrupted so even a small change could translate into gains in their function."
In a forthcoming trial, the team will study the effect of TMS on people with early loss of memory ability. But Dr Voss cautioned that "years" of further research were needed to determine whether the technique was safe or effective enough to help people with Alzheimer's or other conditions that affect memory.