ELECTRIC CURRENT TO BRAIN BOOSTS MEMORY
Stimulating a
particular region in the brain via non-invasive delivery of electrical current
using magnetic pulses, called Transcranial Magnetic Stimulation, improves
memory, reports a new Northwestern Medicine® study
The discovery opens a
new field of possibilities for treating memory impairments caused by conditions
such as stroke, early-stage Alzheimer's disease, traumatic brain injury,
cardiac arrest and the memory problems that occur in healthy aging.
"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," said
senior author Joel Voss, assistant professor of medical social sciences at Northwestern
University Feinberg School of Medicine. "This noninvasive stimulation
improves the ability to learn new things. It has tremendous potential for
treating memory disorders."
The study will be
published August 29 in Science.
The study also is the
first to demonstrate that remembering events requires a collection of many
brain regions to work in concert with a key memory structure called the
hippocampus -- similar to a symphony orchestra. The electrical stimulation is
like giving the brain regions a more talented conductor so they play in closer
synchrony.
"It's like we
replaced their normal conductor with Muti," Voss said, referring to
Riccardo Muti, the music director of the renowned Chicago Symphony Orchestra.
"The brain regions played together better after the stimulation."
The approach also has
potential for treating mental disorders such as schizophrenia in which these
brain regions and the hippocampus are out of sync with each other, affecting
memory and cognition.
TMS Boosts Memory
The Northwestern study
is the first to show TMS improves memory long after treatment. In the past, TMS
has been used in a limited way to temporarily change brain function to improve
performance during a test, for example, making someone push a button slightly
faster while the brain is being stimulated. The study shows that TMS can be
used to improve memory for events at least 24 hours after the stimulation is
given.
Finding the Sweet Spot
It isn't possible to
directly stimulate the hippocampus with TMS because it's too deep in the brain
for the magnetic fields to penetrate. So, using an MRI scan, Voss and
colleagues identified a superficial brain region a mere centimeter from the
surface of the skull with high connectivity to the hippocampus. He wanted to
see if directing the stimulation to this spot would in turn stimulate the
hippocampus. It did.
"I was astonished
to see that it worked so specifically," Voss said.
When TMS was used to
stimulate this spot, regions in the brain involved with the hippocampus became
more synchronized with each other, as indicated by data taken while subjects
were inside an MRI machine, which records the blood flow in the brain as an
indirect measure of neuronal activity.
The more those regions
worked together due to the stimulation, the better people were able to learn
new information.
How the Study Worked
Scientists recruited
16 healthy adults ages 21 to 40. Each had a detailed anatomical image taken of
his or her brain as well as 10 minutes of recording brain activity while lying
quietly inside an MRI scanner. Doing this allowed the researchers to identify
each person's network of brain structures that are involved in memory and well
connected to the hippocampus. The structures are slightly different in each
person and may vary in location by as much as a few centimeters.
"To properly
target the stimulation, we had to identify the structures in each person's
brain space because everyone's brain is different," Voss said.
Each participant then
underwent a memory test, consisting of a set of arbitrary associations between
faces and words that they were asked to learn and remember. After establishing
their baseline ability to perform on this memory task, participants received
brain stimulation 20 minutes a day for five consecutive days.
During the week they
also received additional MRI scans and tests of their ability to remember new
sets of arbitrary word and face parings to see how their memory changed as a
result of the stimulation. Then, at least 24 hours after the final stimulation,
they were tested again.
At least one week
later, the same experiment was repeated but with a fake placebo stimulation.
The order of real stimulation and placebo portions of the study was reversed
for half of the participants, and they weren't told which was which.
Both groups performed
better on memory tests as a result of the brain stimulation. It took three days
of stimulation before they improved.
"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."
In addition, the MRI
showed the stimulation caused the brain regions to become more synchronized
with each other and the hippocampus. The greater the improvement in the
synchronicity or connectivity between specific parts of the network, the better
the performance on the memory test. "The more certain brain regions worked
together because of the stimulation, the more people were able to learn
face-word pairings, " Voss said.
Using TMS to stimulate
memory has multiple advantages, noted first author Jane Wang, a postdoctoral
fellow in Voss's lab at Feinberg. "No medication could be as specific as
TMS for these memory networks," Wang said. "There are a lot of
different targets and it's not easy to come up with any one receptor that's
involved in memory."
The Future
"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," Voss said.
His current study was
with people who had normal memory, in whom he wouldn't expect to see a big
improvement because their brains are already working effectively.
"But 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," Voss said.
In an upcoming trial,
Voss will study the electrical stimulation's effect on people with early-stage
memory loss.
Voss cautioned that
years of research are needed to determine whether this approach is safe or
effective for patients with Alzheimer's disease or similar disorders of memory.
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