Studying decision making in rats using a contextual visual discrimination task: Detection and prevention of alternative behavioral strategies

Background: The neural bases of decision-making and contextual sensory discriminations have traditionally been studied in primates, highlighting the role of the prefrontal cortex in cognitive control and flexibility. With the advent of molecular tools to manipulate and monitor neuronal activity, these processes have increasingly been studied in rodents. However, rodent tasks typically consist of two-alternative forced choice paradigms that usually feature coarse sensory discriminations and no contextual dependence, limiting prefrontal involvement in task performance.

New method: To circumvent these limitations, we developed a novel contextual visual discrimination task that lends itself to rigorous psychophysical analyses. In this task, rats learn to detect left-right differences in one dimension (e.g. luminance or speed) depending on context while ignoring another (e.g. speed or luminance, respectively). Depending on trials, speed and luminance can be greater on the same side (congruent trials) or on opposite sides (incongruent trials).

Results: Rats learned the task in four phases: nose-poking and lever-pressing (∼7 days), discriminating left-right differences in one dimension (∼20 days), discriminating left-right differences in a second dimension (∼10 days), and discriminating left-right differences in one of the two dimensions depending on context (∼2.5 months). A 20:80 ratio of congruent to incongruent trials is used to prevent rats from adopting alternative strategies.

Comparison with existing methods: This task is comparable to contextual sensory discrimination tasks used in monkeys. Few equivalent tasks exist in rodents.

Conclusions: This task will allow investigators to use the full neuroscientific armamentarium to study contextual neural coding in the rat prefrontal cortex.