| It’s a classic upper middle class dilemma:
Should we buy a perfect second home in a place that takes hours
to get to, or should we settle for something closer but not as
nice? In the rodent world, an equivalent decision-making situation
might be, "Was the food I liked better down this alley or
over there?"
By discovering that particular rat brain neurons combine or "integrate" dissimilar
pieces of information (e.g. location versus reward), researchers
have begun to learn how the brain controls decision-making and
goal-oriented behaviors. Examples of these include foraging and
navigation in animals and--in humans--whether to buy a particular
second home or, in general, whether to favor a long-term benefit
over immediate gratification.
Led by Dr. Zach Mainen of Cold Spring Harbor Laboratory on Long
Island, the study represents the first time that brain neurons
have been shown to integrate spatial and reward information. Its
results contrast with a previous "pure economic" view
that neurons in the orbitofrontal cortex (or OFC) are involved
solely in assessing value.
Moreover, the study--published this week in Neuron--has implications
for understanding pathological conditions in humans that affect
decision-making, motivation, and emotions such as addiction, depression,
obsessive-compulsive disorder, autism, and other disorders of thought
or mood.
"
Ultimately, we’re trying to understand how groups of neurons
participate in the creation of perception, awareness, and goal-oriented
behavior," says Mainen. "With this study, we’re
getting some of the first concrete clues about how the brain represents
an animal’s goals."
The research was spearheaded by graduate student Claudia Feierstein,
who recorded the activity of OFC neurons while rats performed an
odor discrimination task that they had previously learned to accomplish.
In the task, the animal receives a test odor ("A" or "B")
by poking its nose into a centrally located odor port. Next, the
animal chooses odor A or odor B as being the same as the test odor
by poking its nose into a choice port located to its right (odor
A) or left (odor B). If the animal chooses correctly, it receives
a reward (a drop of water). Click link below to play a movie of
this task.
TwoAlternativeOdorDiscrimination.mov
As expected, many of the neurons actively signaled "I’m
getting a reward" when the animal moved right or left, i.e.
toward odor A or odor B.
Surprisingly, however, several of the OFC neurons signaled "I’m
getting the reward to my right" whereas several others signaled "I’m
getting the reward to my left."
Mainen says that one of his next steps will be to examine what
happens in the brain while the animals are learning to recognize
new odors. "This may or may not figure into those experiments,
but we’ve already found that about one quarter of the rats
we use are significantly below average in learning. Their motivation
levels also vary quite a bit, which might be interesting to explore
as well."
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