Magnetic brain stimulation may boost memory
- Aging, dementia, and brain injury can reduce people’s capacity to form new memories of events in their lives, which experts term episodic memory.
- A study suggests that low-frequency magnetic stimulation of a particular part of the brain enhances the formation of this kind of memories.
- Much more research is necessary, but the discovery could provide a way to improve memory in people with conditions such as dementia.
Memories of our experiences, or episodic memories, help us define who we are as individuals.
Episodic memory also allows us to function effectively on a day-to-day basis, from remembering where we put our phone to what groceries we need to buy on a shopping trip.
The ability to form new memories declines slowly with age, but brain injury and conditions such as Alzheimer’s disease can result in a severe, debilitating loss of episodic memory.
Some prescription drugs can help improve memory in people with Alzheimer’s disease, but their effects are limited and short-lived.
Manufacturers market nonprescription supplements known as nootropics to enhance memory, though there is little scientific evidence of their effectiveness.
A group of researchers led by the University of Glasgow in the United Kingdom may have stumbled upon a completely new way to boost episodic memory, using magnetic pulses.
They were conducting research into a phenomenon known as voluntary forgetting when they noticed that slow magnetic pulses seemed to enhance memory.
They used an established technology called repetitive transcranial magnetic stimulation (rTMS) to deliver the pulses to the left side of the volunteers’ foreheads, over a region called the dorsolateral prefrontal cortex (DLPFC).
A second study by the same researchers appears to confirm the memory-enhancing effect.
They have reported their results in the journal PLOS Biology.
“We were quite surprised when we saw these effects in the first study, which was designed to investigate a different question,” says Prof. Simon Hanslmayr, Ph.D., one of the researchers and senior author of the paper.
“Therefore, we needed to replicate the effects in a second experiment to see whether this is real, and indeed, it seems to be,” he adds.
The researchers analyzed data from 40 healthy volunteers whom they asked to memorize lists of words while their brains were stimulated with rTMS at 1 hertz (Hz) (1 pulse per second).
Half of the volunteers received pulses to their left DLPFC, while the other half received pulses over a control brain area known as the vertex, which is not involved in memory.
Those who had their left DLPFC magnetically stimulated were significantly better at recalling the words in a subsequent test.
To exclude the possibility that one group simply had better memory skills than the other, the scientists repeated the experiment. This time, 24 volunteers each received magnetic stimulation of the DLPFC, followed by stimulation of the vertex, or the other way round, in separate trials.
At the same time, the scientists used EEG to monitor electrical activity in the participants’ brains.
Once again, the volunteers recalled significantly more words if their DLPFC was stimulated during memorization.
On the EEG readout, the slow magnetic pulses appeared to reduce the power of brain waves in the beta frequency range over a part of the brain called the parietal cortex.
Previous research has found a link between a reduction in the power of the beta part of the EEG spectrum, from 13 to 30 Hz, and memory formation.
Stimulation and inhibition
Prof. Hanslmayr told Medical News Today that it is not clear what this change in beta activity means, but other studies suggest that it may reflect a change in the balance between nervous stimulation, or “excitation,” and inhibition.
“Our stimulation [of the DLPFC] seemed to have tipped this balance towards more inhibition, which seems beneficial for memory encoding,” he said.
“More work is needed to better understand why and how this benefits memory,” he added.
Until this basic science has been done, he said, it was too early to talk about clinical applications.
“However, our findings could be of relevance for patients with Alzheimer’s disease who gradually lose the ability to form episodic memories,” he explained. “Interestingly, the balance between excitation and inhibition is severely affected in these patients.”
Prof. Hanslmayr believes future studies should investigate whether rTMS can help restore this balance and improve memory in Alzheimer’s disease.
He said he and his colleagues hope to investigate the effect further and explore possible applications to treat conditions that involve problems with memory, such as Alzheimer’s disease.
In their paper, the scientists note that their study had some potential limitations.
In particular, in common with other studies that involve rTMS, they recorded EEG changes shortly after magnetic stimulation rather than simultaneously.
This is because the magnetic pulses themselves disrupt EEG measurements — a glitch known as an experimental artifact.
They write that subsequent changes in the electrical activity of the parietal cortex may be a “rebound effect” following this disruption.
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