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August 18, 2011
from
ScienceDaily Website
Every day we make thousands of tiny
predictions - when the bus will arrive, who is knocking on the door,
whether the dropped glass will break.
Now, in one of the first studies of its
kind, researchers at Washington University in St. Louis are
beginning to unravel the process by which the brain makes these
everyday prognostications.
While this might sound like a boon to day traders, coaches and gypsy
fortune tellers, people with early stages of neurological diseases
such as schizophrenia, Alzheimer's and Parkinson's diseases could
someday benefit from this research. In these maladies, sufferers
have difficulty segmenting events in their environment from the
normal stream of consciousness that constantly surrounds them.
The researchers focused on the mid-brain dopamine system (MDS),
an evolutionarily ancient system that provides signals to the rest
of the brain when unexpected events occur.
Using functional MRI (fMRI),
they found that this system encodes prediction error when viewers
are forced to choose what will happen next in a video of an everyday
event.
Predicting the near future is vital in guiding behavior and is a key
component of theories of perception, language processing and
learning, says Jeffrey M. Zacks, PhD, WUSTL associate
professor of psychology in Arts & Sciences and lead author of a
paper on the study in a forthcoming issue of the Journal of
Cognitive Neuroscience.
"It's valuable to be able to run
away when the lion lunges at you, but it's super-valuable to be
able to hop out of the way before the lion jumps," Zacks says.
"It's a big adaptive advantage to look just a little bit over
the horizon."
Zacks and his colleagues are building a
theory of how predictive perception works. At the core of the theory
is the belief that a good part of predicting the future is the
maintenance of a mental model of what is happening now.
Now and then, this model needs updating,
especially when the environment changes unpredictably.
"When we watch everyday activity
unfold around us, we make predictions about what will happen a
few seconds out," Zacks says. "Most of the time, our predictions
are right.
"Successful predictions are associated with the subjective
experience of a smooth stream of consciousness. But a few times
a minute, our predictions come out wrong and then we perceive a
break in the stream of consciousness, accompanied by an uptick
in activity of primitive parts of the brain involved with the
MDS that regulate attention and adaptation to unpredicted
changes."
Zacks tested healthy young volunteers
who were shown movies of everyday events such as washing a car,
building a LEGO model or washing clothes. The movie would be watched
for a while, and then it was stopped.
Participants then were asked to predict what would happen five
seconds later when the movie was re-started by selecting a picture
that showed what would happen, and avoiding similar pictures that
did not correspond to what would happen.
Half of the time, the movie was stopped just before an event
boundary, when a new event was just about to start. The other half
of the time, the movie was stopped in the middle of an event. The
researchers found that participants were more than 90 percent
correct in predicting activity within the event, but less than 80
percent correct in predicting across the event boundary.
They were also less confident in their
predictions.
"This is the point where they are
trying hardest to predict the future," Zacks says. "It's harder
across the event boundary, and they know that they are having
trouble. When the film is stopped, the participants are heading
into the time when prediction error is starting to surge.
That is, they are noting that a
possible error is starting to happen. And that shakes their
confidence. They're thinking, 'Do I really know what's going to
happen next?' "
Zacks and his group were keenly
interested in what the participants' brains were doing as they tried
to predict into a new event.
In the functional MRI experiment, Zacks and his colleagues saw
significant activity in several midbrain regions, among them the
substantia nigra - "ground zero for
the dopamine signaling system" - and in a set of nuclei called the
striatum.
The substantia nigra, Zacks says, is the part of the brain
hit hardest by Parkinson's disease, and is important for controlling
movement and making adaptive decisions.
Brain activity in this experiment was revealed by fMRI at two
critical points:
Mid-brain responses,
"really light up at hard times, like
crossing the event boundary and when the subjects were told that
they had made the wrong choice," Zacks says.
Zacks says the experiments provide a
"crisp test" of his laboratory's prediction theory.
They also offer hope of targeting these
prediction-based updating mechanisms to better diagnose early stage
neurological diseases and provide tools to help patients.
Story Source
Journal Reference
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Jeffrey M. Zacks, Christopher A.
Kurby, Michelle L. Eisenberg, Nayiri Haroutunian. Prediction
Error Associated with the Perceptual Segmentation of
Naturalistic Events. Journal of Cognitive Neuroscience,
2011; 1 DOI:
10.1162/jocn_a_00078
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