Transcript Orbital Frontal Cortex Slides

Orbitofrontal Cortex and Its Contribution to
Decision-Making
•Structural Anatomy
of the OFC
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Part of the PFC and occupies the ventral
region of the frontal lobe
The OFC integrates sensory and other
sources of information to calculate a
reward.
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It contributes to person’s decision making
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Has 5 architectonic sub-regions
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47/12, 10, 11, 13, and 14
The 47/12 region receives highly
processed visual and auditory
information.
The 13 region acts as a bridge
between the lateral and medial layers
of the brain. Primary olfactory and
gustatory cortex project to this region.
The 11 region is involved in planning,
reasoning, and decision making.
Connections in the OFC
OFC connections are compatible with a structure that
integrates sensory and reward information.
Three prominent features:
1. Frontal cortex receives information from all sensory modalities
- Area 47/12 processes visual information (from inferior temporal cortex), audio
information, somatosensory input (from secondary somatosensory cortex,) and
inputs from polysensory areas (like superior temporal cortex)
2. OFC has only weak motor connections, some exist between
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47/12 and supplementary eye fields
Area 13 and ventral premotor cortex
PFC connects with cingulate motor area
Dorsal and later PFC connect with premotor cortex
3. OFC extensively connects with areas of the limbic system
- Including the amygdala, cingulate gyrus, and the hippocampus
- Influences the autonomic nervous system through the hypothalamus and other
brainstem structures
Damage to the OFC
Story of Elliot
Elliot was diagnosed with a brain tumor and had it successfully removed. The surgery
left him with bilateral damage to his OFC. Neuropsychologist ran test on Elliot but
found no evidence of brain damage.
- Tested intelligence, memory, reading and writing comprehension, verbal fluency,
visuospatial abilities, and facial recognition; also ran test designed specifically for
frontal lobe processes, such as working memory, rule switching, and cognitive
estimation did NOT show any deficits
Although Elliot did not show any brain damage in the areas listed above, he was
affected by the damage in his OFC:
Life Before the surgery
-Excelled in college
-Rose through the ranks of his career
-Happily married
-Seen as a role model and natural leader
Life After the surgery
-Devoiced his wife
- Quit his job and trouble holding a job
-Lost his money to a scam artist
-Lost contact with friends and family
-Remarried a prostitute and divorced
Damage to the OFC leaves our cognitive abilities intact, but demolishes our
ability to make decisions in everyday life.
Two underlying theories:
Stimulus-Reward Learning and Flexible Behavior
• Monkey and Man:
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Research paradigm: Reverse contingencies
• It’s all logical inference:
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Inability to reverse stimulus-reward associations
unable to modify his/her behavior in response to negative feedback
• OFC is the eraser
Underlying theory
Somatic Marker Hypothesis
• Core idea:
• Bodily states (somatic markers) corresponding to the emotions produced
while evaluating different courses of action help to facilitate normal decisionmaking.
• Somatic markers are associations between reinforcing stimuli that induce an
associated physiological affective state. These somatic-marker associations can
reoccur during decision-making and bias our cognitive processing (e.g., a
burnt child dreads the fire).
• Underlying assumption:
• James-Lange theory of emotions: Behaviors first, then the
emotion
• Explanations for Deficits of Decision-making
• Iowa gambling task
• Stimulus-reward reversals
Early theory
• 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.
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
• Monkeys were given a choice between
different volumes of different types of liquid,
Fruit juice and water. (Wallis)
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, (without considering
basic desires of hunger and thirst), would it
prefer the food or the water?
Is Reward Relative?
• Difficult to measure reward in absolute terms
• Reward is relative to the specific situation
• Value of reward depends on other potential
rewards
• Lab situation explored ability of subjects to
experience regret
• Subjects with OFC damage had no regret when
making the wrong choice
Relative and Non-Relative Information
• There is both relative and non-relative
information processed in the brain.
• We believe most to be relative.
• Non-Relative information includes those
processes involved in basic needs. Ex:
Breathing
Need and Reward
• Our needs are often complex, encompassing
– physiological ,
– cognitive,
– emotional, and
– social factors,
• but in all cases, these needs affect how
valuable a reward is. A reward must satisfy a
need. If it does not satisfy a need, it is not
valuable.
• A need is essential for a reward.
Could there be a time when reward
has no value?
• To be put simply, when there is no need.
• In theory, if a person had absolutely
everything they could ever need or want, it
would be impossible to reward them.
However, that is impossible. People can be
rich but not be fulfilled spiritually or
emotionally and could be rewarded in one of
those facets.
Con’t
• Other times a reward might not be valuable
could be:
– Coming off of drug addiction and chemical
imbalance
– Winning the lottery the day after losing a close
family member
Neutral Events
• A “secondary reinforcer” that carries indirect
reward only through the its association with a
“primary reinforcer”
• Needed to the extent that we need primary
reinforcers (i.e. moneyfood, water, shelter)
• Neutral events act as a means of getting what
we really need, but are not needed in of
themselves
Neuroeconomics
• A field that relates models of the parameters that
animals/humans use to make everyday decisions to patterns of
neuronal firing.
• The 3 main parameters that one considers when making a
decision:
– 1. The expected reward or payoff
– 2. The cost in terms of time and energy
• Although an outcome may be highly desirable, we may
not pursue it if the cost to obtain it is too great.
– 3. The probability of success
• We need to assess the uncertainty in obtaining the
outcome. i.e., risk, or misinterpreting sensory
information
•Each arm of the T-maze varies the amount of the
reward given.
•The arm with the most reward has a stipulation:
it required more effort to access (barriers the
mice had to climb) or it required a waiting period
before a gate opens.
•Lesions of MPFC: mice chose smaller reward
that required less effort
•Lesions of OFC: mice chose the smaller reward
with more immediate access
Neuroeconomics vs. Emotion
•.
• Considers payoff, cost, and probability of success. This is
mostly done by the frontal cortex.
•Considers physiological arousal, mood, and motivation.
Involves the limbic system and autonomic nervous system
•However, emotion plays a large role in neuroeconomics!
•Humans rarely make decisions using completely rational
methods, such as evaluating cost/benefit ratios.
•Much of the time, our decisions are based on our
desires and feelings.
• Neuroeconomics factors in emotion to help us make
clearer predictions about how we decide things.