one of most Mysterious Brain's Switchboard Operator Revealed
A mysterious region deep in the human brain could be
where we sort through the onslaught of stimuli from the outside world and focus
on the information most important to our behavior and survival, Princeton
University researchers have found.
The researchers report in the journal Science that an
area of our brain called the pulvinar regulates communication between clusters
of brain cells as our brain focuses on the people and objects that need our
attention. Like a switchboard operator, the pulvinar makes sure that separate
areas of the visual cortex -- which processes visual information -- are
communicating about the same external information, explained lead author Yuri
Saalmann, an associate research scholar in the Princeton Neuroscience Institute
(PNI). Without guidance from the pulvinar, an important observation such as an
oncoming bus as one is crossing the street could get lost in a jumble of other
stimuli.
Saalmann said these findings on how the brain transmits
information could lead to new ways of understanding and treating
attention-related disorders, such as attention deficit hyperactivity disorder
(ADHD) and schizophrenia. Saalmann worked with senior researcher Sabine Kastner,
a professor in the Department of Psychology and the Princeton Neuroscience
Institute; and PNI researchers Xin Li, a research assistant; Mark Pinsk, a
professional specialist; and Liang Wang, a postdoctoral research associate.
The researchers developed a new technique to trace direct
communication between clusters of neurons in the visual cortex and the
pulvinar. The team produced neural connection maps using magnetic resonance
imaging (MRI), then placed electrodes along those identified communication
paths to monitor brain signals of macaques. The researchers trained the monkeys
to play a video game during which they used visual cues to find a specific
shape surrounded by distracting information. As the macaques focused, Saalmann
and his colleagues could see that the pulvinar controlled which parts of the
visual cortex sent and received signals.
Saalmann explains the Princeton findings as follows:
"A fundamental problem for the brain is that there
is too much information in our natural environment for it to be processed in
detail at the same time. The brain instead selectively focuses on, or attends
to, the people and objects most relevant to our behavior at the time and
filters out the rest. For instance, as we cross a busy city street, our brain
blocks out the bustle of the crowd behind us to concentrate more on an oncoming
bus.
"The transmission of behaviorally relevant
information between various parts of the brain is tightly synchronized. As one
brain area sends a signal about our environment, such as that a bus is
approaching, another brain area is ready to receive it and respond, such as by
having us cross the street faster. A persistent question in neuroscience,
though, is how exactly do different brain areas synchronize so that important
information isn't lost in the other stimuli flooding our brains.
"Our study suggests that a mysterious area in the
center of the brain called the pulvinar acts as a switchboard operator between
areas on the brain's surface known as the visual cortex, which processes visual
information. When we pay attention to important visual information, the
pulvinar makes sure that information passing between clusters of neurons is
consistent and relevant to our behavior.
"These results could advance the understanding of
the neural mechanisms of selective attention and how the brain transmits
information. This is a necessary step in developing effective treatment
strategies for medical disorders characterized by a failure of attention
mechanisms. These conditions include ADHD, schizophrenia and spatial neglect,
which is an inability to detect stimuli often observed following stroke.
"For our study, we trained monkeys to play a video
game in which they paid attention to visual cues in order to detect different
target shapes. We simultaneously recorded brain activity in the pulvinar and
two different areas of the visual cortex. We could see a clear connective path
from one portion of the cortex to another, as well as connective paths from the
pulvinar to the cortex. When the monkeys paid attention to the visual cues, the
pulvinar sent electrical pulses to synchronize particular groups of brain cells
in the visual cortex to allow them to communicate effectively.
"A challenge in this study was that we needed to
record the activity of cells that were 'speaking' directly with each other so
we could trace the line of communication. But there are billions of brain
cells. Traditionally, finding a cell-to-cell connection is as likely as
randomly selecting two people talking on cell phones in different parts of New
York City and discovering that they were speaking to each other.
"To 'listen in' on a direct cell conversation, we
developed a new approach of using electrodes to record groups of brain cells
that were anatomically connected. We first mapped neural connections in the
brain via diffusion tensor imaging, which uses an MRI scanner to measure the
movement of water along neural connections. We then used these images to
implant electrodes at the endpoints of the neural connections shared by the
pulvinar and the visual cortex.
"Our mapping of these communication networks and our
finding that the pulvinar is vital to attention prompts a new consideration of
the mechanisms behind higher cognitive function. We challenge the common notion
that these functions depend exclusively on the cerebral cortex, the outermost
layer of the brain responsible for decision-making, attention and language,
among other abilities. It also suggests that the prevailing view that visual
information is transmitted solely through a network of areas in the visual
cortex needs to be revised to include the pulvinar as an important regulator of
neural transmission."
Image Source: http://www.sxc.hu/photo/1214707
Image Source: http://www.sxc.hu/photo/1214707
Post a Comment