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.

4 drops of water 1 drop of fruit juice 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. 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