Orbitofrontal lesions in rats impair reversal but not acquisition of go, no-go odor discriminations.

Recent evidence suggests that orbitofrontal cortex lesions cause an inability to withhold inappropriate responses particularly when learned behavior must be modified to reflect changes in the likely outcome or consequence of responding. By this account, orbitofrontal cortex should not be necessary for acquisition of simple discrimination problems, but should be critical for acquiring reversals of those problems. However, previous work in rats has shown orbitofrontal cortex to be critical for withholding responses even in a simple go, no-go discrimination task. Here we have reexamined the contribution of rat orbitofrontal cortex to acquisition and reversal of go, no-go odor discrimination problems. Contrary to prior reports, we found that rats with lesions of the orbitofrontal cortex acquired novel discrimination problems at the same rate as controls. Impairments were evident in lesioned rats when the response contingencies of the odors in the discrimination problem were reversed. These findings suggest that orbitofrontal cortex is not necessary for inhibiting responses unless responses must be altered to reflect changing relationships between cues and outcomes.