Study finds neurons that encode the outcomes of actions
Date:
March 25, 2022
Source:
Massachusetts Institute of Technology
Summary:
A group of neurons in the brain's striatum encodes information about
the potential outcomes of different decisions. These cells become
particularly active when a behavior leads a different outcome than
what was expected, which the researchers believe helps the brain
adapt to changing circumstances.
FULL STORY ==========================================================================
When we make complex decisions, we have to take many factors into
account. Some choices have a high payoff but carry potential risks;
others are lower risk but may have a lower reward associated with them.
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A new study from MIT sheds light on the part of the brain that helps us
make these types of decisions. The research team found a group of neurons
in the brain's striatum that encodes information about the potential
outcomes of different decisions. These cells become particularly active
when a behavior leads a different outcome than what was expected, which
the researchers believe helps the brain adapt to changing circumstances.
"A lot of this brain activity deals with surprising outcomes, because
if an outcome is expected, there's really nothing to be learned. What
we see is that there's a strong encoding of both unexpected rewards and unexpected negative outcomes," says Bernard Bloem, a former MIT postdoc
and one of the lead authors of the new study.
Impairments in this kind of decision-making are a hallmark of many neuropsychiatric disorders, especially anxiety and depression. The
new findings suggest that slight disturbances in the activity of these
striatal neurons could swing the brain into making impulsive decisions
or becoming paralyzed with indecision, the researchers say.
Rafiq Huda, a former MIT postdoc, is also a lead author of the paper,
which appears in Nature Communications. Ann Graybiel, an MIT Institute Professor and member of MIT's McGovern Institute for Brain Research,
is the senior author of the study.
Learning from experience The striatum, located deep within the brain,
is known to play a key role in making decisions that require evaluating outcomes of a particular action. In this study, the researchers wanted to
learn more about the neural basis of how the brain makes cost-benefit decisions, in which a behavior can have a mixture of positive and
negative outcomes.
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To study this kind of decision-making, the researchers trained mice
to spin a wheel to the left or the right. With each turn, they would
receive a combination of reward (sugary water) and negative outcome
(a small puff of air). As the mice performed the task, they learned to
maximize the delivery of rewards and to minimize the delivery of air
puffs. However, over hundreds of trials, the researchers frequently
changed the probabilities of getting the reward or the puff of air,
so the mice would need to adjust their behavior.
As the mice learned to make these adjustments, the researchers recorded
the activity of neurons in the striatum. They had expected to find
neuronal activity that reflects which actions are good and need to be
repeated, or bad and that need to be avoided. While some neurons did
this, the researchers also found, to their surprise, that many neurons
encoded details about the relationship between the actions and both
types of outcomes.
The researchers found that these neurons responded more strongly when
a behavior resulted in an unexpected outcome, that is, when turning
the wheel in one direction produced the opposite outcome as it had in
previous trials. These "error signals" for reward and penalty seem to
help the brain figure out that it's time to change tactics.
Most of the neurons that encode these error signals are found in the
striosomes -- clusters of neurons located in the striatum. Previous
work has shown that striosomes send information to many other parts of
the brain, including dopamine-producing regions and regions involved in planning movement.
"The striosomes seem to mostly keep track of what the actual outcomes
are," Bloem says. "The decision whether to do an action or not, which essentially requires integrating multiple outcomes, probably happens
somewhere downstream in the brain." Making judgments
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The findings could be relevant not only to mice learning a task, but
also to many decisions that people have to make every day as they weigh
the risks and benefits of each choice. Eating a big bowl of ice cream
after dinner leads to immediate gratification, but it might contribute
to weight gain or poor health.
Deciding to have carrots instead will make you feel healthier, but you'll
miss out on the enjoyment of the sweet treat.
"From a value perspective, these can be considered equally good,"
Bloem says.
"What we find is that the striatum also knows why these are good, and it
knows what are the benefits and the cost of each. In a way, the activity
there reflects much more about the potential outcome than just how
likely you are to choose it." This type of complex decision-making is
often impaired in people with a variety of neuropsychiatric disorders, including anxiety, depression, schizophrenia, obsessive-compulsive
disorder, and posttraumatic stress disorder. Drug abuse can also lead
to impaired judgment and impulsivity.
"You can imagine that if things are set up this way, it wouldn't be
all that difficult to get mixed up about what is good and what is bad,
because there are some neurons that fire when an outcome is good and
they also fire when the outcome is bad," Graybiel says. "Our ability to
make our movements or our thoughts in what we call a normal way depends
on those distinctions, and if they get blurred, it's real trouble."
The new findings suggest that behavioral therapy targeting the stage at
which information about potential outcomes is encoded in the brain may
help people who suffer from those disorders, the researchers say.
The research was funded by the National Institutes of Health/National
Institute of Mental Health, the Saks Kavanaugh Foundation, the William
N. and Bernice E.
Bumpus Foundation, the Simons Foundation, the Nancy Lurie Marks Family Foundation, the National Eye Institute, the National Institute of
Neurological Disease and Stroke, the National Science Foundation, the
Simons Foundation Autism Research Initiative, and JSPS KAKENHI.
========================================================================== Story Source: Materials provided by
Massachusetts_Institute_of_Technology. Original written by Anne
Trafton. Note: Content may be edited for style and length.
========================================================================== Journal Reference:
1. Bernard Bloem, Rafiq Huda, Ken-ichi Amemori, Alex S. Abate, Gayathri
Krishna, Anna L. Wilson, Cody W. Carter, Mriganka Sur, Ann
M. Graybiel.
Multiplexed action-outcome representation by striatal
striosome-matrix compartments detected with a mouse cost-benefit
foraging task. Nature Communications, 2022; 13 (1) DOI:
10.1038/s41467-022-28983-5 ==========================================================================
Link to news story:
https://www.sciencedaily.com/releases/2022/03/220325122706.htm
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