Abstract
Associative learning is encoded under anesthesia and involves the medial prefrontal cortex (mPFC). Neuronal activity in mPFC increases in response to a conditioned stimulus (CS+) previously paired with an unconditioned stimulus (US) but not during presentation of an unpaired stimulus (CS−) in anesthetized animals. Studies in conscious animals have shown dissociable roles for different mPFC subregions in mediating various memory processes, with the prelimbic (PL) and infralimbic (IL) cortex involved in the retrieval and extinction of conditioned responding, respectively. Therefore PL and IL may also play different roles in mediating the retrieval and extinction of discrimination learning under anesthesia. Here we used in vivo electrophysiology to examine unit and local field potential (LFP) activity in PL and IL before and after auditory discrimination learning and during later retrieval and extinction testing in anesthetized rats. Animals received repeated presentations of two distinct sounds, one of which was paired with footshock (US). In separate control experiments animals received footshocks without sounds. After discrimination learning the paired (CS+) and unpaired (CS−) sounds were repeatedly presented alone. We found increased unit firing and LFP power in PL and, to a lesser extent, IL after discrimination learning but not after footshocks alone. After discrimination learning, unit firing and LFP power increased in PL and IL in response to presentation of the first CS+, compared to the first CS−. However, PL and IL activity increased during the last CS− presentation, such that activity during presentation of the last CS+ and CS− did not differ. These results confirm previous findings and extend them by showing that increased PL and IL activity result from encoding of the CS+/US association rather than US presentation. They also suggest that extinction may occur under anesthesia and might be represented at the neural level in PL and IL.
Highlights
IntroductionUndergoing fear learning while anesthetized can result in learned fear expression after recovery from anesthesia if epinephrine is given during learning (Weinberger et al, 1984; Gold et al, 1985)
In certain circumstances associative learning occurs under general anesthesia
We have recently shown similar results in the basolateral amygdala (BLA) during auditory discrimination learning under anesthesia, where BLA activity increases in response to CS+, but not CSÀ, presentation after learning (Fenton et al, 2013)
Summary
Undergoing fear learning while anesthetized can result in learned fear expression after recovery from anesthesia if epinephrine is given during learning (Weinberger et al, 1984; Gold et al, 1985). We have recently shown similar results in the basolateral amygdala (BLA) during auditory discrimination learning under anesthesia, where BLA activity increases in response to CS+, but not CSÀ, presentation after learning (Fenton et al, 2013). These findings are comparable to changes in LA and BLA activity during discriminative fear learning (Maren et al, 1991; Collins and Pare , 2000; Herry et al, 2008)
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