Orbitofrontal cortex lesions disrupt risk assessment in a novel serial decision-making task for rats.

Neurobiological mechanisms of decision-making have been shown to be modulated by a number of frontal brain regions. Among those areas, the orbitofrontal cortex (OFC) is thought to play an important role in the decision of behavioral actions when faced with alternative options of ambiguous outcome. Here we present a novel neurobehavioral task to study affective decision-making in the rat, based on evaluation of consecutive choices between two levers associated with rewards of different value and probability. Two groups of animals were studied; a sham control group (n=6) and an OFC-lesioned group (n=7). In the first 30 trials both groups had similar preference patterns but at the end of the 90 trials of the task both groups developed specific preferences. The control group systematically preferred the lever associated with smaller but more reliable rewards (low risk lever) while the OFC lesion group preferred the high risk lever (index of preference of 0.21+/-0.21 vs. -0.45+/-0.10; t-test, P<0.05). Analysis of choice persistence (i.e. choosing the same lever in consecutive trials) suggests that the OFC-lesioned group became less sensitive to risk, seeking large rewards irrespective of their success probability.