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

Geoffrey Schoenbaum, Summer L. Nugent, Michael P. Saddoris and Barrry Setlow

NEUROREPORT (2002)

DOI: 10.1097/00001756-200205070-00030

The conceptual gap or the scientific question: what are the functional roles of the orbitofrontal cortex (OFC) in discrimination learning?

How the authors proposed the question: conflicting observations were reported about the roles of the OFC in simple discrimination learning. So the authors tried to re-examine it by using a distinct lesion approach. So always keep it in mind: in scientific research, where there are conflicts, there are chances.

Brief summary: the authors shown that the lesions of the OFC had no effects on the initial learning of odor discrimination learning, impaired the first reversal learning, but improved the later serial reversal learning.

How the authors tell the story: the authors first displayed the conventional understanding (response inhibition) about the functions of the OFC based on the behavioral observations after OFC lesions: disinhibition, perseveration and impulsive responses. And then set it as a to be overturned target theory, falsified it from the front, suspended it by promoting the alternative. So this story is a A-Not A-but B structure.The story was well constructed, although the data were not so convincing.

The experiment and conclusion is quite simple and intuitive. But the underlying reasoning deserves special attention. I was impressed by the argument they made about the no-effect observation on the initial learning after OFC lesions: 'It is important to note that the spared discrimination performance in OFC-lesioned rats in Phase-I does not argue against this interpretation (the interpretation was : OFC is important for using incentive information to guide behavior).' And then they proposed an alternative: 'Intact learning in these subjects is presumably based on associative structures that do not involve goal representations, such as stimulus-response (habit) learning [Ref. 13, Goal-directed instrumental action: contingency and incentive learning and their cortical substrates, Neuropharmacology ,1998].' What's the meaning of 'associative structures'? They referenced a classic behavioral study in 1998. Let's go through that paper later.

So my impression is the most enlightening part of this paper resides in the Discussion. From the discussion we can learn from the authors how to find the position of a study in the field, or even in history, especially from those senior researchers. Do not skip it indifferently!

The ongoing question(s) inspired by the current study: is the improvement at the later reversals a general phenomenon by OFC lesions? OFC lesions impair the first reversal learning, but improve the later reversals. It's pretty intriguing if it was the real case. Let's dig more literatures to verify it.