Activation of a remote (1-year old) emotional memory interferes with the retrieval of a newly formed hippocampus-dependent memory in rats.

The persistent intrusion of remote traumatic memories in people with post-traumatic stress disorder (PTSD) may contribute to the impairment of their ongoing hippocampal and prefrontal cortical functioning. In the current work, we have developed a rodent analogue of the intrusive memory phenomenon. We studied the influence of the activation of a remote traumatic memory in rats on their ability to retrieve a newly formed hippocampus-dependent memory. Adult male Sprague-Dawley rats were given inhibitory avoidance (IA) training, and then 24 h or 1, 6 or 12 months later, the same rats were trained to learn, and then remember across a 30-min delay period, the location of a hidden escape platform in the radial-arm water maze (RAWM). When IA-trained rats spent the 30-min delay period in the IA apparatus, they exhibited intact remote (1-year old) memory of the shock experience. More importantly, activation of the rats' memory of the shock experience profoundly impaired their ability to retrieve the newly formed spatial memory of the hidden platform location in the RAWM. Our finding that reactivation of a remote emotional memory exerted an intrusive effect on new spatial memory processing in rats provides a novel approach toward understanding how intrusive memories of traumatic experiences interfere with ongoing cognitive processing in people with PTSD.