Conditioned contextual fear memory to assess natural forgetting and cognitive enhancement in rats

Aversively established contextual fear memory manifests itself in robust freezing behavior, often lasting several weeks or months. Therefore, this approach is amenable to investigate the underlying neural circuitries by lesion or inactivation of specific brain regions or to test efficacy of substances that disrupt either the ability to acquire the association or to retrieve memories. In contrast, investigation of memory enhancement using this technique is time intensive since the non-treated control group naturally forgets the learned association only weeks after acquisition. Pharmacological interventions have been used to overcome this time span by disrupting memory at any time point, however, limiting it a mechanistic model of reversal of impairments instead of studying memory enhancement. Here, we investigated several parameters of the cued and contextual fear conditioning (CFC) protocol such that, while memory acquisition is established, loss of fear association occurs within a shorter time frame, allowing studies of memory enhancement in the context of natural forgetting. We found that three predictive tone-cues, each separated from a 0.3 mA foot shock by an interstimulus interval of 2 s and a pre-exposure to the context enables the investigation of enhanced contextual memory 7 d post training without the necessity of inducing pharmacological lesions.