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."
Journal Reference:
- Y. B. Saalmann, M. A. Pinsk, L. Wang, X. Li, S. Kastner. The Pulvinar Regulates Information Transmission Between Cortical Areas Based on Attention Demands. Science, 2012; 337 (6095): 753 DOI: 10.1126/science.1223082
Courtesy: ScienceDaily
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