Lesions and the Valuation of Information

Information economics is based on the premise that information is a scarce commodity. Because its acquisition is costly, the economic actor weighs the value of an additional unit of information against his/her highest valued alternative. In this sense, information is no different than any tangible good that can be bought and sold. The September issue of Science includes a paper by Rudebeck, Buckley, Walton and Rushworth that integrates neuroecon and info-econ via a lesion study on macaques:

We assessed how selective lesions of ACC gyrus (ACC_G), ACC sulcus (ACC_S), or lateral orbital and ventral prefrontal cortex (PFv+o) affect the way macaques value social information.

And how were the monkeys’ valuations measured?

Measurements were made of latencies to pick up food items in the presence of fear-inducing stimuli (toy snakes) in experiment 1, social stimuli (short films of other macaques) in experiment 2, or neutral control objects. The latencies indexed the macaques’ assessment of the value of obtaining further information about the stimulus before reaching and reflected their relative valuation of the stimulus in contrast to the incentive of the food.

When confronted with the fear-inducing information,

[Control animals with no lesion] were consistently reluctant to take food from above a moving toy snake, but the case was significantly different for both the PFv+o group and the ACC_S group…There were no significant differences between the ACC_G and controls.

The behavior of the ACC_G group, however, was significantly different from the other three groups when social information was presented:

[Controls] were slower to pick up food in the presence of a large staring male, a female macaque with visible sexual perineal swellings, and a midsized macaque making affiliative lip-smacking gestures…The ACC_G group remained uninterested in any of the images of other macaques…By contrast, comparable modulations of reaching latencies were seen in PFv+o and ACC_S groups as in the controls, and there were no significant differences between any of these three groups. 

The results enable the researchers to draw the following conclusions:

The ACC region critical for mediating the valuation of social stimuli appears to be the ACC_G immediately rostral and dorsal to the genu of the corpus callosum and includes areas 32 and rostral area 24. 

Complete ACC_S lesions only affected the mild fear task significantly and not the social task. 

(Note that Brodmann’s area 32 refers to the dorsal ACC, while BA 24 refers to the ventral ACC. The experiment described here suggests that the lesions to the dorsal ACC and the ventral ACC may have differential effects that sum to produce the observed social deviancy.)

If the latency measure legitimately represents the monkeys’ opportunity cost of acquiring more information, these results suggest the following economic interpretation: (1) An ACC_G lesion decreases monkeys’ willingness to pay for social information; (2) Lesions of the ACC_S and lateral orbital and ventral prefrontal cortex increase monkeys’ willingness to pay for information relating to fearful stimuli.