The large red blob (left) indicates an increase in the timing, or
synchronization, between brain waves measured over the medial frontal cortex
and right lateral prefrontal cortex. This enhanced timing across brain regions
specifically occurred at low frequencies, right after participants viewed
negative feedback. This increase in synchronization corresponded with
improvement in behavior related to learning and self-control. Credit: Robert
Reinhart
Two brain regions—the medial frontal and lateral prefrontal cortices—control most executive function. Robert Reinhart used high-definition transcranial alternating current stimulation (HD-tACS) to synchronize oscillations between them, improving brain processing. De-synchronizing did the opposite.
Robert Reinhart
calls the medial frontal cortex the "alarm bell
of the brain."
"If you make an
error, this brain area fires," says Reinhart, an assistant professor of
psychological and brain sciences at Boston University. "If I tell you that
you make an error, it also fires. If something surprises you, it fires."
Hit a sour note on the piano and the medial frontal cortex lights up, helping
you correct your mistake as fast as possible. In healthy people, this region of
the brain works hand in hand (or perhaps lobe in lobe) with a nearby region,
the lateral prefrontal cortex, an area that stores
rules and goals and also plays an important role in changing our decisions and
actions.
"These are
maybe the two most fundamental brain areas involved with executive
function and self-control," says Reinhart, who used a new
technique called high-definition transcranial alternating current stimulation
(HD-tACS) to stimulate these two regions with electrodes placed on a
participant's scalp. Using this new technology, he found that improving the
synchronization of brain waves, or oscillations, between these two
regions enhanced their communication with each other, allowing participants to
perform better on laboratory tasks related to learning and self-control.
Conversely, de-synchronizing or disrupting the timing of the brain waves in
these regions impaired participants' ability to learn and control their
behavior, an effect that Reinhart could quickly fix by changing how he
delivered the electrical stimulation. The work, published October 9, 2017, in
the journal Proceedings of the National Academy of Sciences (PNAS),
suggests that electrical
stimulation can quickly—and reversibly—increase or decrease
executive function in healthy people and change their behavior. These findings
may someday lead to tools that can enhance normal brain function, possibly
helping treat disorders from anxiety to autism.
"We're always looking for a link between brain activity and
behavior—it's not enough to have just one of those things. That's part of what
makes this finding so exciting," says David Somers, a BU professor of
psychological and brain sciences, who was not involved with the study. Somers
likens the stimulation to a "turbo charge" for your brain. "It's
really easy to mess things up in the brain but much harder to actually improve
function."
Research has recently suggested that populations of millions of
cells in the medial frontal cortex and the lateral prefrontal cortex may communicate
with each other through the precise timing of their synchronized oscillations,
and these brain rhythms appear to occur at a relatively low frequency (about
four to eight cycles per second). While scientists have studied these waves
before, Reinhart is the first to use HD-tACS to test how these populations of
cells interact and whether their interactions are behaviorally useful for
learning and decision-making. In his work, funded by the National Institutes of
Health, Reinhart is able to use HD-tACS to isolate and alter these two specific
brain regions, while also recording participants' electrical brain activity via
electroencephalogram (EEG).
"The science is much stronger, much more precise than what's
been done earlier," says Somers.
In his first round of studies, Reinhart tested 30 healthy
participants. Each subject wore a soft cap fitted with electrodes that
stimulated brain activity, while additional electrodes monitored brain waves.
(The procedure is safe, noninvasive, and doesn't hurt, says Reinhart.
"There's a slight tingling for the first 30 seconds," he says,
"and then people habituate to it.") Then, for 40 minutes,
participants performed a time-estimation learning task, pressing a button when
they thought 1.7 seconds had passed. Each time, the computer gave them
feedback: too fast, too slow, or just right.
Reinhart tested each of the 30 participants three times, once
up-regulating the oscillations, once disrupting them, and once doing nothing.
In tests where Reinhart cranked up the synchrony between the two brain regions,
people learned faster, made fewer errors, and—when they did make an
error—adjusted their performance more accurately. And, when he instead
disrupted the oscillations and decreased the synchrony—in a very rough sense,
flicking the switch from "smart" to "dumb"—subjects made
more errors and learned slower. The effects were so subtle that the people
themselves did not notice any improvement or impairment in the task, but the
results were statistically significant.
Reinhart then replicated
the experiment in 30 new participants, adding another study parameter by
looking at only one side of the brain at a time. In all cases, he found that
the right hemisphere of the brain was more relevant to changing behavior.
Then came the most
intriguing part of the study. Thirty more participants came in and tried the
task. First, Reinhart temporarily disrupted each subject's brain
activity, watching as their brain waves de-synchronized and their
performance on the task declined. But this time, in the middle of the task,
Reinhart switched the timing of the stimulation—again, turning the knob from
"dumb" to "smart." Participants recovered their original
levels of brain synchrony and learning behavior within minutes.
"We were shocked by
the results and how quickly the effects of the stimulation could be
reversed," says Reinhart.
Though Reinhart cautions
that these results are very preliminary, he notes that many psychiatric and
neurological disorders—including anxiety, Parkinson's, autism, schizophrenia,
ADHD, and Alzheimer's—demonstrate disrupted oscillations. Currently, most of
these disorders are treated with drugs that act on receptors throughout the
brain. "Drugs are really messy," says Reinhart. "They often
affect very large regions of brain." He imagines, instead, a future with
precisely targeted brain stimulation that acts only on one critical node of a
brain network, "like a finer scalpel." Reinhart's next line of
research will test the technology on people with anxiety disorders.
There is also, of course,
the promise of what the technology might offer to healthy brains. Several
companies already market brain stimulation devices that claim to
both enhance learning and decrease anxiety. YouTube videos show how to make
your own, with double-A batteries and off-the-shelf electronics, a practice
Reinhart discourages. "You can hurt yourself," he says. "You can
get burned and have current ringing around your head for days."
He does, however, see the
appeal. "I had volunteers in previous research who came back and said,
'Hey, where can I get one of these? I'd love to have it prior to an
exam,'" he says. "That was after we debriefed them and they were
reading the papers about it."
Somers notes that there are
still many questions to answer about the technology before it goes mainstream:
How long can the effect last? How big can you make it? Can you generalize from
a simple laboratory task to much more complicated endeavors? "But the
biggest question," says Somers, "is how far you can go with this
technology."
"Think about any given
workday," says Somers. "You need to be really 'on' for one meeting,
so you set aside some time on your lunch break for some brain stimulation.
I think a lot of people would be really into that—it would be like three cups of
coffee without the jitters."
More information: Disruption and rescue of interareal theta
phase coupling and adaptive behavior, PNAS(2017).
Journal reference: Proceedings of the National Academy of Sciences
Provided by: Boston University
https://medicalxpress.com/news/2017-10-turbo-brain-synchronizing-specific-oscillations.html
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