Where We Change Our Mind In The Cerebral Cortex
June 1, 2006
Whether finding your way through an unfamiliar neighborhood to a friend's
house or deciding on a political candidate, your brain is adept at adapting. It
can make decisions based on incomplete information and update those decisions
based on new information.
The nature of such sophisticated decision making in the cerebral cortex, which
is responsible for high-level processing, has been "poorly studied and
little understood," according to Wako Yoshida and Shin Ishii of the Nara
Institute of Science and Technology. Now, however, in an article in the June 1,
2006, Neuron, they describe experiments that enabled them to tease apart how
different regions of the cerebral cortex process uncertain information and
integrate it into decision making.
In particular, their aim was to analyze subjects' navigation through a virtual
maze, to explore how different cortical regions function in solving
"partially observable decision-making problems."
"In navigation tasks, such as that investigated here, an individual must
constantly maintain an estimate as to his/her current location as a guide for
deciding the next turn," they wrote, "but in the absence of
incontrovertible a priori information, this estimate is best represented by the
subject's belief. As information is acquired through observation, this belief
may become increasingly convincing or alternatively may be discarded in favor of
a new one. This is an intuitive way of making estimations that are appropriate
for many real-world behaviors, adopted also by a wide variety of intelligent
machines.…," they wrote.
In their experiments, the researchers first taught volunteer subjects the layout
of a computer-generated 3D "wire-frame" maze. Then, while the
subjects' brains were being scanned using functional magnetic resonance, the
researchers "placed" the subjects in different parts of the maze and
analyzed activation of cerebral cortical regions as the subjects made a series
of decisions to navigate their way to a specified goal. Functional MRI involves
using harmless magnetic fields and radio waves to image blood flow in brain
regions, which reflects activity.
Importantly, Yoshida and Ishii used sophisticated statistical probabilistic
analysis of the subjects' movements to overcome a major obstacle to such
studies. That obstacle is that the beliefs of the subjects during the experiment
could not be determined unequivocally; thus, those beliefs could not be
correlated with brain function.
However, the researchers' statistical analysis of the subject's navigation
decisions enabled them to infer which of two "cognitive states" the
subject was in, to give the researchers insight into which cortical regions were
active during the states. One such cognitive state was a belief about where the
subject was in the maze, and the other was a set of "operant" states.
These operant states were a "proceed or update mode" or a
"reevaluate or back-track mode."
Analyzing the brain regions active during these states, Yoshidi and Ishii
pinpointed which regions of the subjects' cerebral cortex were active during the
different processes involved in "changing their minds." Specifically,
the researchers found that "belief maintenance" processes are
performed principally by a region called the anterior prefrontal cortex, and
"belief back-track" processes occur in the medial prefrontal cortex.
"Our results provide evidence that activity in different regions of the
prefrontal cortex reflect critical computational components involved in decision
making in uncertain environments," concluded the researchers. "This
fits well with the proposed role of these regions in decision making, which is
likely to be crucial in complex real-world environments. We also illustrate the
utility of statistical model-based inference and regression in delineating key
task parameters that may be represented in spatially distinct brain
regions," they concluded.
Heidi Hardman
hhardman@cell.com
Cell Press
http://www.cellpress.com/