Putting fear in context: Elucidating the role of the retrosplenial cortex in context discrimination in rats

The retrosplenial cortex (RSC), which receives visuo-spatial sensory input and interacts with numerous hippocampal memory system structures, has a well-established role in contextual learning and memory. While it has been demonstrated that RSC function is necessary to learn to recognize a single environment that is directly paired with an aversive event, the role of the RSC in discriminating between two different contexts remains largely unknown. To address this, first order (Experiment 1) and higher order (Experiment 2) fear conditioning paradigms were conducted with sham and RSC-lesioned rats. In Experiment 1 rats were exposed to one context in which shock was delivered and to a second, distinct context without shock. Their ability to discriminate between the contexts was assessed during a re-exposure test. In a second experiment, a new cohort of RSC-lesioned rats was exposed to two contexts made distinct through visual, olfactory and auditory stimuli. In a subsequent conditioning phase, the salience of one of the auditory stimuli was paired to an aversive footshock while the other was not. Similar to Experiment 1, freezing behavior was analyzed upon re-exposure to the contexts in the absence of both the auditory cue and the footshock. The results revealed that RSC is not necessary for rats to use contextual information to successfully discriminate between two contexts under the relatively simple demands involved in this first order conditioning paradigm but that context discrimination is impaired when the processing of complex and/or ambiguous contextual stimuli is required to select appropriate behavioral responses.