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Thursday, 22 June 2017

22-07-2017 - Interesting - Mapping how words leap from brain to tongue


Most adults can quickly and effortlessly
recall as many as 100,000 regularly used
words when prompted, but how the brain
accomplishes this has long boggled
scientists.
Credit: © BillionPhotos.com / Fotolia
When you look at a picture of a mug, the
neurons that store your memory of what a
mug is begin firing. But it's not a pinpoint
process; a host of neurons that code for
related ideas and items bowl, coffee, spoon,
plate, breakfast -- are activated as well. How
your brain narrows down this smorgasbord of
related concepts to the one word you're truly
seeking is a complicated and poorly
understood cognitive task. A new study led by
San Diego State University neuroscientist
Stephanie Ries, of the School of Speech,
Language, and Hearing Sciences, delved into
this question by measuring the brain's cortical
activity and found that wide, overlapping
swaths of the brain work in parallel to retrieve
the correct word from memory.
Most adults can quickly and effortlessly recall
as many as 100,000 regularly used words
when prompted, but how the brain
accomplishes this has long boggled scientists.
How does the brain nearly always find the
needle in the haystack? Previous work has
revealed that the brain organizes ideas and
words into semantically related clusters. When
trying to recall a specific word, the brain
activates its cluster, significantly reducing the
size of the haystack.
To figure out what happens next in that
process, Ries and colleagues asked for help
from a population of people in a unique
position to lend their brainpower to the
problem: patients undergoing brain surgery to
reduce their epileptic seizures. Before surgery,
neurosurgeons monitor their brain activity to
figure out which region of the brain is
triggering the patients' seizures, which
requires the patients to wear a grid of dozens
of electrodes placed directly on top of the
cortex, the outermost folded layers of the
brain.
While the patients were hooked up to this grid
in a hospital and waiting for a seizure to
occur, Ries asked if they'd be willing to
participate in her research. Recording brain
signals directly from the cortical surface
affords neuroscientists like Ries an
unparalleled look at exactly when and where
neurons are communicating with one another
during tasks.
"During that period, you have time to do
cognitive research that's impossible to do
otherwise," she said. "It's an extraordinary
window of opportunity."
For the recent study, nine patients agreed to
participate. In 15 minute-sessions, she and her
team would show the patients an item on a
computer screen -- musical instruments,
vehicles, houses
then ask them to name it
as quickly as possible, all while tracking their
brain activity.
They measured the separate neuronal
processes involved with first activating the
item's conceptual cluster, then selecting the
proper word. Surprisingly, they discovered the
two processes actually happen at the same
time and activate a much wider network of
brain regions than previously suspected. As
expected, two regions known to be involved in
language processing lit up, the left inferior
frontal gyrus and the posterior temporal
cortex. But so did several other regions not
traditionally linked to language, including the
medial and middle frontal gyri, the researchers
reported in the Proceedings of the National
Academy of Sciences .
"This work shows the word retrieval process in
the brain is not at all as localized as we
previously thought," Ries said. "It's not a clear
division of labor between brain regions. It's a
much more complex process."
Learning exactly how the brain accomplishes
these tasks could one day help speech-
language pathologists devise strategies for
treating disorders that prevent people from
readily accessing their vocabulary.
"Word retrieval is usually effortless in most
people, but it is routinely compromised in
patients who suffer from anomia, or word
retrieval difficulty," Ries said. "Anomia is the
most common complaint in patients with
stroke-induced aphasia, but is also common in
neurodegenerative diseases and normal aging.
So it is critical to understand how this process
works to understand how to help make it
better."

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