:: adgruntie :: Neurons and Choosing between goods

+ Researchers at Harvard Medical School report in the April 23 issue of Nature that they have identified neurons that encode the values that subjects assign to different items. The activity of these neurons might facilitate the process of decision-making that occurs when someone chooses between different goods.

In his experiment, Padoa-Schioppa had macaque monkeys choose between two types of juice offered in different amounts. In some trials, the monkey chose between one drop of grape juice (which monkeys prefer) and one drop of apple juice. In other trials, the monkey chose between one drop of grape juice and two drops of apple juice, etc. Behaviorally, Padoa-Schioppa observed a trade-off between juice type and juice quantity. The monkey might choose grape juice when one or two drops of apple juice were available. However, the monkey might be indifferent between the two juices when offered one drop of grape juice versus three drops of apple juice, and might always choose the apple juice if four or more drops were available. This indicates that the value the monkey assigns to one drop of grape juice is roughly equal to the value the monkey assigns to three drops of apple juice.

On the basis of such choice pattern, Padoa-Schioppa could correlate the activity of neurons in the OFC directly with the value assigned to the two juices. For example, the activity of one particular neuron could be low when the monkey chose one drop of grape juice or when it chose three drops of apple juice (low value). The activity of the same neuron might be medium-high when the monkey chose two drops of grape juice or when it chose six drops of apple juice (medium-high value). And the activity of the same neuron might be high when the monkey chose three drops of grape juice or when it chose 10 drops of apple juice (high value). This means that the activity of such OFC neurons encodes the value chosen by the monkey independently of the physical characteristics of the juice--its taste, quantity, etc.

Padoa-Schioppa also found that other neurons in the OFC encode the value of only one of the two juices offered to the monkey. Some neurons encoded the value of the grape juice, while other neurons encoded the value of the apple juice. "The monkey's choice may be based on the activity of these neurons," says Padoa-Schioppa.

An important aspect of the results is that neurons in the OFC encode the economic value of offered and chosen goods independently of the particular way the goods are offered to the monkey, and independently of the specific action the animal uses to signal its choice. For example, OFC neurons encoding the value of apples and oranges would do so regardless of whether the apple is offered on the right and the orange on the left, or vice versa.

(Via future pundit)