- Dorsal stream of the brain which generates rhythmic electrical pulses called theta waves is responsible for auditory memory.
- The theta waves were enhanced using transcranial magnetic stimulation (TMS) and its effects were measured on the subjects' memory performance.
- Application of TMS helped to manipulate the activity of the theta waves, which helped in improving the subjects' auditory memory task.
How sound (auditory) memory works in the brain has been revealed by a new research, that also demonstrates a means to improve it.
A neural network of the brain called the dorsal stream is responsible for aspects of auditory memory. Inside the dorsal stream are the rhythmic electrical pulses called theta waves, but the role of these waves in auditory memory were not fully understood.
‘The potential of transcranial magnetic stimulation (TMS) to improve brain performance also has clinical implications and could be used for the loss of memory caused by neurodegenerative diseases such as Alzheimer's.’
The research team at the Montreal Neurological Institute of McGill University recruited 17 individuals to learn the relationship between theta waves and auditory memory.
They were assigned auditory memory tasks that required them to recognize a pattern of tones when it was reversed.
The tasks of the individuals were recorded with a combination of magnetoencephalography (MEG) and electroencephalography (EEG).
The amplitude and frequency signatures of theta waves in the dorsal stream were determined using MEG/EEG while the subjects worked on the memory tasks. It also revealed where the theta waves were coming from in the brain.
Transcranial Magnetic Stimulation
In the next step, the activity of theta waves were enhanced using transcranial magnetic stimulation (TMS) at the same theta frequency to the subjects while they performed the same tasks, and the effects of the enhancement was measured on the subjects' memory performance.
The auditory memory task of the participants considerably improved when the TMS was applied.
When the TMS matched the rhythm of natural theta waves in the brain, the performance improved but when the TMS was arrhythmic, there was no effect on performance. This shows that the manipulation of theta waves and not just the application of TMS, alters performance.
"For a long time the role of theta waves has been unclear," says Sylvain Baillet, one of the study's co-senior authors. "We now know much more about the nature of the mechanisms involved and their causal role in brain functions. For this study, we have built on our strengths at The Neuro, using MEG, EEG and TMS as complementary techniques."
"Now we know human behavior can be specifically boosted using stimulation that matched ongoing, self-generated brain oscillations," said Philippe Albouy, the study's first author. "Even more exciting is that while this study investigated auditory memory, the same approach can be used for multiple cognitive processes such as vision, perception, and learning."
In future, TMS could be used to compensate for the loss of memory caused by neurodegenerative diseases such as Alzheimer's.
"The results are very promising, and offer a pathway for future treatments," says Robert Zatorre, one of the study's co-senior authors. "We plan to do more research to see if we can make the performance boost last longer, and if it works for other kinds of stimuli and tasks. This will help researchers develop clinical applications."
This study was published in the journal Neuron
- Philippe Albouy et al. Selective Entrainment of Theta Oscillations in the Dorsal Stream Causally Enhances Auditory Working Memory Performance . Neuron; (2017) doi.org/10.1016/j.neuron.2017.03.015