A technique that uses magnetic pulses to stimulate nerve cells in the brain was used in the lab to improve memory, and could one day help treat people with Alzheimer’s and other diseases with memory impairment.
Postdoctoral researcher Phillipe Albouy and his supervisors Robert Zatorre, a senior fellow in CIFAR’s Azrieli Program in Brain, Mind & Consciousness, and Sylvain Baillet of the MNI’s brain imaging centre, used the non-invasive technique called transcranial magnetic stimulation (TMS) to boost memory in healthy volunteers.
The McGill researchers published their study in the journal Neuron. It builds on previous work of Zatorre’s in which he pinpointed an area of the brain responsible for auditory working memory, a type of short-term memory that allows us to temporarily store and use information. This brain area was part of the dorsal stream, which carries auditory information to the rest of the brain and allows us to perceive and reproduce musical sounds and speech.
In the new study, the researchers wanted to explore the role of ongoing rhythmic electrical pulses found in the dorsal stream called theta waves. Until now their role has been unclear.
“The main idea was to see whether we could identify brain activity patterns that were associated with specific aspects of auditory working memory in order to modulate them” said Zatorre.
Albouy suggested they could use TMS to enhance people’s natural theta waves in the dorsal stream and see if that would improve auditory memory.
They recruited 17 people and gave them a test that required them to remember and compare short streams of musical notes presented forwards and backwards. Then they applied TMS pulses to the dorsal region at the same rate as the subjects’ natural theta waves and had them perform the tasks again.
When TMS was applied subjects were better at remembering and comparing the patterns of notes. However, this was only the case when TMS was applied at the same rhythm as the brain’s own theta waves. When it was applied arrhythmically it had no effect. The researchers also found that the power of the theta waves increased as they synchronized with the TMS. The more synchronized the waves were, the more a subject’s performance improved. Finally, the researchers also found that TMS improved overall communication across all regions of the dorsal stream.
“We think that’s really critical because it shows a causal influence,” said Zatorre. He says the results show a clear link between the stimulation, the increased theta power and the improved memory, suggesting that it’s the manipulation of theta waves, not just the application of TMS that improves memory.
Albouy suggested that the same approach could be useful for enhancing other cognitive processes such as vision, perception and learning.
Next Zatorre and Albouy will explore how long the effects of this TMS memory boost last and whether they can add up over time. Ultimately, the aim is to determine whether it is possible to improve working memory in populations that have some impairment, such as those with Alzheimer’s.
“There are many interesting possible applications. There’s a whole lot more that needs to be done. I’d say we’re at least a decade away from actually having applications,” said Zatorre.