The neural basis of reversal learning: An updated perspective

Abstract

Reversal learning paradigms are among the most widely used tests of cognitive flexibility and have been used as assays, across species, for altered cognitive processes in a host of neuropsychiatric conditions. Based on recent studies in humans, non-human primates, and rodents, the notion that reversal learning tasks primarily measure response inhibition, has been revised. In this review, we describe how cognitive flexibility is measured by reversal learning and discuss new definitions of the construct validity of the task that are serving as a heuristic to guide future research in this field. We also provide an update on the available evidence implicating certain cortical and subcortical brain regions in the mediation of reversal learning, and an overview of the principal neurotransmitter systems involved.

Keywords: amygdala; dopamine; frontal cortex; glutamate; serotonin; striatum.

Figure 1. Publications of reports on reversal learning in rodent, monkey, and human subjects

Pubmed search terms “reversal learning” from 1950–2014. The early-to-mid 2000’s witnessed the steepest rise in the number of publications on reversal learning. Reversal learning continues to be a widely-used paradigm for assessing cognitive function, with an almost equal focus on rodent, monkey and human subjects.

Figure 2. Reversal learning assessments using touchscreens in rodent, monkey, and human subjects

Despite some differences in the paradigms, there is more convergence and comparability of methods for testing reversal learning across species than disagreement. Shown is an example of the touchscreen platform across species. In rats and monkeys the relationship between stimuli and outcomes are either fully (deterministic) or partially predictive (probabilistic), whereas reversal paradigms in humans are almost always probabilistic.

Figure 3. Sub-processes in reversal learning that contribute to a revised definition for the construct validity of the task

The widely-accepted idea that reversal leaning paradigms primarily measure inhibitory control (1) of responding, has fallen out of favor. Instead, reversal learning paradigms all likely test the ability to learn from rewards and non-rewards upon choosing different stimuli (2), estimate the likelihood or prior probability that reversals can occur (3), and/or generate an understanding of task or option space (4).