| Perceptual Decision-Making Hub Pinpointed in
A perceptual decision-making hub at the front of the brain makes
the call on whether you’re looking at a face or a house
and likely many other things scientists at the NIH’s
National Institute of Mental Health (NIMH) have discovered. It works
by gauging the strength of competing signals from lower brain areas
specialized for recognizing different objects, report Drs. Hauke
Heekeren, Leslie Ungerleider, and colleagues, in the October 14,
Although earlier studies in monkeys had suggested that such a decision-making
hub exists, its location in the human brain was not previously known.
The researchers took advantage of the fact that it takes the brain
longer to figure out what it’s looking at when an image is
very blurred or obscured like trying to recognize people
standing on a street corner in a downpour versus on a clear day.
Hard to discern images evoke a relatively slower and reduced response
in the decision-making area, as it mulls the strength of competing
signals from specialized visual processing areas, where neurons
fire only to the extent that they see certain objects or features,
the monkey studies showed.
While their brain activity was monitored with functional magnetic
resonance imaging (fMRI), twelve healthy subjects pressed buttons
to indicate whether they saw a face or a house, as images flashed
on a computer monitor. Some of the images were so noisy that they
were barely discernable, reducing accuracy from 95 percent to 82
The researchers looked for a site in the brain’s frontal
cortex showing the telltale reduced activity during hard trials
that coincided with activity in temporal lobe visual processing
circuits that they had determined are specialized for responding
to faces and houses, respectively. An area in the left front of
the brain (dorsolateral prefrontal cortex) responded with more activity
when images were easier to identify than when they were hard to
discern. These responses also jibed with the difference between
the signals emanating from the face and house specialized regions,
indicating that it was the likely hub of perceptual decision-making.
“It’s a relatively simple subtraction mechanism, but
for a noisier stimulus, the decision may be a closer call,”
explained Heekeren. “Responses of each specialized region
may differ by only a little bit, and so it takes the brain longer
to weigh each signal and make a decision.”
The dorsal lateral prefrontal cortex site is also activated by
other tasks, suggesting that it likely has general decision-making
functions, note the researchers.
Also participating in the study were Drs. Sean Marrett and Peter
NIMH is part of the National Institutes of Health (NIH), the Federal
Government's primary agency for biomedical and behavioral research.
NIH is a component of the U.S. Department of Health and Human Services.
in an MRI scanner pressed buttons to indicate whether they saw
a face or a house for each of a series of obscured images flashed
on a screen that were either easy (top) or hard (bottom) to
||Researchers identified specialized visual processing regions
low in the brain’s temporal lobe that responded selectively
to faces (yellow) and houses (green). Activity in response to the
noisiest/hardest images was less clear-cut than to less noisy/easy
ones, leading to a slower and dampened response by the decision-making
area in the frontal cortex.
|fMRI images show decision-making area in left dorsolateral prefrontal cortex.
Source: NIMH Laboratory of Brain and Cognition