Failing memory is one of the (many) drawbacks of old age, but can also impact younger people suffering stroke, early-stage Alzheimer's disease, traumatic brain injury and cardiac arrest. In a breakthrough that opens up the potential for new treatments for memory impairments in the young and old, researchers at Northwestern University in the US have shown that electrical stimulation of the brain can improve memory, with the benefits lasting long after treatment.
Unlike Deep Brain Stimulation, in which electrodes are implanted into the brain and which has also shown promise for enhancing memory as well as for the treatment of depression, the Northwestern study involves a non-invasive method called Transcranial Magnetic Stimulation (TMS). This uses magnetic pulses to induce electrical activity in particular regions of the brain and has previously been shown to enhance the learning ability of rats and shown promise in the treatment of migraines.
For their study, the Northwestern team enlisted 16 healthy adults between the ages of 16 and 40 and took a detailed anatomical image of their brains as well as using an MRI scanner to record their brain activity for 10 minutes as they lay quietly. This provided an overview of the individuals' brain structures involved in memory that are well connected to a key memory structure called the hippocampus and which would be targeted for stimulation.
To establish their baseline ability, the subjects were then given a set of arbitrary associations between faces and words that they were asked to learn and remember. This was followed with the participants being given TMS for 20 minutes a day for five consecutive days.
Over this period, the subjects also received additional MRI scans and had their memory tested with new sets of arbitrary word and face pairings so see how their memory changed as a result of the stimulation. Then, a minimum of 24 hours after the final TMS application, the subjects were tested again.
A minimum of one week later, the experiment was repeated but with a fake placebo stimulation. Half of the participants received the real stimulation first, followed by the placebo stimulation, with the order reversed for the other half. Neither group was told which order they received the tests in.
The results showed that brain stimulation led to better performance on the memory tests, with it taking three days of stimulation before the improvements occurred.
"They remembered more face-word pairings after the stimulation than before, which means their learning ability improved," Voss said. "That didn’t happen for the placebo condition or in another control experiment with additional subjects."
Although TMS has previously been used to temporarily change brain function and improve performance in a test as the brain is being stimulated, the Northwestern team says their study is the first to show that TMS improves memory for events for at least 24 hours after the subject receives brain stimulation.
The team says their study is also the first to show that the recall of events involves many different brain regions working together with the hippocampus. The MRIs showed that the TMS caused the brain regions to become more synchronized with each other and the hippocampus, with the greater the improvement in the synchronicity or connectivity, the better the subject's performance in the memory test.
Voss likens this coordination between these various regions to a symphony orchestra, with the electrical stimulation acting like a talented conductor to allow the various regions to work in closer synchrony.
"It’s like we replaced their normal conductor with Muti," said Joel Voss, assistant professor of medical social sciences at Northwestern University Feinberg School of Medicine, referring to Riccardo Muti, the music director of the renowned Chicago Symphony Orchestra. "The brain regions played together better after the stimulation."
Although the tests were conducted on people with normal memory, in whom the researchers didn't expect to see great improvements as their brains were already working effectively, the researchers believe the effects on people with brain damage or a memory disorder would be even more evident, with even a small change translating into gains in their function.
To put this theory to the test, Voss will now study the effect of TMS on people with early-stage memory loss. However, he cautioned that years of research would be required before it is known whether the technique is safe or effective for people with Alzheimer's disease or similar memory disorders.
The team's study was published in the journal Science and is detailed in the video below.
Source: Northwestern University