Roles of orbitofrontal and insular cortices in processing reward variables

Delays and risks are important in evaluation of subjective value. We performed two experiments to examine how these reward variables are processed in our brain. Although choices of both humans and animals are more strongly influenced by immediate than delayed rewards, methodological limitations have made it difficult to estimate the precise form of temporal discounting in animals. In the present study, we sought to characterize temporal discounting in rats and to test the role of the orbitofrontal cortex (OFC) in this process. Rats were trained in a novel intertemporal choice task in which the sequence of delay durations was randomized across trials. The animals tended to choose a small immediate reward more frequently as the delay for a large reward increased, and, consistent with previous findings in other species, their choice behavior was better accounted for by hyperbolic than exponential discount functions. In addition, model comparisons showed that the animal’s choice behavior was better accounted for by more complex discount functions with an additional parameter than a hyperbolic discount function. Following bilateral OFC lesions, rats extensively trained in this task showed no significant change in their intertemporal choice behavior. Our results suggest that the rodent OFC may not always play a role in temporal discounting when delays are randomized and/or after extensive training. Risk is essential information in decision making, because it is a universal phenomenon in the environment. Brain imaging studies in humans have shown that anterior insular cortex (AIC) is affected by risk in decision situations. However previous studies have not examined neural activity related to risk in AIC. Moreover, damages in OFC have yielded conflicting results, even they showed altered risky choice behavior. In the present study, we tested neural responses in AIC and in OFC of rats under risk condition. Rats were trained in a Pavlovian conditioning task in which five different auditory cues (1 s) were associated with five different reward probabilities (0%, 25%, 50%, 75% and 100%). Since reward probabilities were symmetric, riskiness is divided into three levels, with the highest risk associated with 50% reward probability, a medium risk with 25% and 75% probabilities, and the lowest risk with 0% and 100% probabilities. Accordingly, neural responses to risk can be dissociated from those to reward probability and expected reward value. Both brain regions represented signals related to risk as well as signals related to expected value, and only the AIC showed multi-phasic activities responded to reward. These results suggest that both AIC and OFC can participate in evaluating subjective value, through conveying signals associated with expected value and risk and through conveying unique signals responded to reward.

Author dc:creator

• 조, 수현

Contributors dc:contributor

• 김, 병곤
• 정, 민환
• 대학원 의생명과학과
• 200624091

• orbitofrontal cortex
• temporal discounting
• intertemporal choice
• anterior insular cortex
• risk
• value
• 안와전두피질
• 섬엽피질
• 위험성
• 효용 가치

Language dc:language

en

Identifier

http://dcoll.ajou.ac.kr:9080/dcollection/jsp/common/DcLoOrgPer.jsp?sItemId=000000014803
000000014803

OAI identifier oai:identifier

oai:repository.ajou.ac.kr:201003/8600