The retrosplenial cortex and object recency memory in the rat

• Published in: The European journal of neuroscience Vol. 45; no. 11; pp. 1451 - 1464
• Main Authors: Powell, Anna L., Vann, Seralynne D., Olarte‐Sánchez, Cristian M., Kinnavane, Lisa, Davies, Moira, Amin, Eman, Aggleton, John P., Nelson, Andrew J. D., Klausberger, Thomas
• Format: Journal Article
• Language: English
• Published: France Wiley Subscription Services, Inc 01-06-2017; John Wiley and Sons Inc
• Subjects: Animal behavior; Animal memory; Animals; Brain - cytology; Brain - physiology; c-Fos protein; Cognitive Neuroscience; Cortex (frontal); c‐fos; Diencephalon; Hippocampus; Lesions; Male; Memory, Long-Term; Memory, Short-Term; Neurons - metabolism; Neurons - physiology; Proto-Oncogene Proteins c-fos - genetics; Proto-Oncogene Proteins c-fos - metabolism; Rats; recognition memory; Rodents; Spatial discrimination learning; Spatial Memory; Subiculum; Temporal cortex; temporal discrimination; Temporal variations; c-fos; subiculum; hippocampus; recognition memory; temporal discrimination
• ISSN: 0953-816X; 1460-9568
• DOI: 10.1111/ejn.13577

It has been proposed that the retrosplenial cortex forms part of a ‘where/when’ information network. The present study focussed on the related issue of whether retrosplenial cortex also contributes to ‘what/when’ information, by examining object recency memory. In Experiment 1, rats with retrosplenial lesions were found to be impaired at distinguishing the temporal order of objects presented in a continuous series (‘Within‐Block’ condition). The same lesioned rats could, however, distinguish between objects that had been previously presented in one of two discrete blocks (‘Between‐Block’ condition). Experiment 2 used intact rats to map the expression of the immediate‐early gene c‐fos in retrosplenial cortex following performance of a between‐block, recency discrimination. Recency performance correlated positively with levels of c‐fos expression in both granular and dysgranular retrosplenial cortex (areas 29 and 30). Expression of c‐fos in the granular retrosplenial cortex also correlated with prelimbic cortex and ventral subiculum c‐fos activity, the latter also correlating with recency memory performance. The combined findings from both experiments reveal an involvement of the retrosplenial cortex in temporal order memory, which includes both between‐block and within‐block problems. The current findings also suggest that the rat retrosplenial cortex comprises one of a group of closely interlinked regions that enable recency memory, including the hippocampal formation, medial diencephalon and medial frontal cortex. In view of the well‐established importance of the retrosplenial cortex for spatial learning, the findings support the notion that, with its frontal and hippocampal connections, retrosplenial cortex has a key role for both what/when and where/when information.
Rats with retrosplenial lesions were impaired at distinguishing the temporal order of objects presented in a continuous series. In a separate group of rats, recency performance correlated positively with levels of c‐fos expression in both granular and dysgranular retrosplenial cortex. In view of the well‐established importance of the retrosplenial cortex for spatial learning, the findings support the notion that the retrosplenial cortex plays a key role in temporal memory.