Transcript Orbitofrontal Cortex and Its Contribution to Decision

Orbitofrontal Cortex and
Its Contribution to
Decision-Making
Group 2
Reward Processing
• The mechanism by
which behavior and
cognitive measures
correlate expected
reward while driving
neuronal response.
Early thinking
• Neuronal response to rewards and
punishment. Same behavioral and cognitive
neuronal sequelae.
• Brain areas extracting the value of choice
should display reward selectivity before those
areas responsible for using the value
information to control behavior and cognition.
• (Wallis & Miller, 2003)- Monkeys primed to
maximize their reward by selecting pictures.
What must we be cautious about…
• Neurons that show different firing rates
depending on the expected reward outcome
are found in different areas of the brain.
• A neuron is not necessarily encoding a reward
just because its firing rate correlates with
some parameters of that reward.
Aspect of Reward in OFC encoding
• Hedonic value: The degree of happiness or
sadness associated with an outcome.
• Incentive value: The degree of desirability of
an outcome.
• OFC: Encoding value of a choice
• Reward selective response: Premotor
readiness exhibited to carry out reaction to
choice.
• Time course
of encoding
neurons
across the
DLPFC and
OFC
population
• Distribution of
peak selectivity
across the
population of
DLPFC and OFC
neurons.
• The OFC
population
reaches its
peak selectivity
about 60ms
before the
DLPFC
population.
• Spike histogram from two single neurons
encoding the expected reward and/or the
monkeys response
Localization of Neurons
• Reward selective neurons are in both DLPFC and
the OFC
• The OFC encodes the value of choice outcome
and then passes this information to the DLPFC
which then uses the information to control
behavior.
Calculating a rewards value
The OFC neurons integrate
multiple sensory features
of a reward to determine
its value.
Rewards involve integration
and trade-off. Everyday
decisions are complex
and often requires us to
weigh the pros and cons
of several variables.
Reward value (cont.)
• Monkeys were given a choice between
different volumes of different types of liquid,
Fruit juice and water.
To make its choice the monkey needed to consider
both variables: the different Volumes and the different
tastes between liquids
The monkey may prefer the fruit juice over water, so if
the volume was the same, then it would choose the juice.
Increasing the volume of the water, would
compensate for its taste.
The firing rates of OFC neurons were more likely to vary with the value of the drinks,
rather than the physical properties (ex: Taste or Volume)
A neuron that was encoding the value of the chosen reward might show a higher
Firing rate when the monkey choose the one drop of juice to the one drop of water,
But the monkey’s firing rate would be the same when choosing one drop of juice to
Four drops of water
To the monkey, the value of 1 drop of juice is equal to four drops of water.
4 drops of water
1 drop of fruit juice
When the value of the two drinks is the same, the neuronal firing rate is
also equivalent.
Patients with OFC damage
• Difficulty integrating the
multiple attributes pertaining to
a decision.
• The OFC is ideal to the
multimodal integration of
parameters necessary to
evaluate an outcome because it
receives input from all sensory
modalities.
• Neuroimaging reveals that
human OFC is activated by
pleasant and unpleasant smells,
sights, sounds and touches, as
well as more abstract rewards
and punishments like receiving
and losing money.
Thought…
• If a monkey was presented with a choice
between food and water/juice, (without
considering basic desires of hunger and thirst),
we feel that it will take the food.
• The food is a bigger reward,
and is generally offered less
often then food and water,
and thus is more appealing.
• We feel that desire is an
additional factor that should
be considered in the value of
reward