The retrosplenial cortex is necessary for path integration in the dark.

An increasing amount of data indicates that the retrosplenial cortex (RSC) plays a role in navigation and spatial memory. Moreover, it has been suggested that the RSC integrates mnemonic spatial features of the environment with self-motion information therefore enabling accurate path integration in darkness. This hypothesis rests on data obtained from animals trained in spatial memory tasks involving the conjoint use of allothetic and idiothetic information [8]. We examined the contribution of the RSC when animals are submitted to a path integration task with minimal memory requirement in light and dark. We found that RSC-lesioned rats exhibited a path integration deficit in the dark but not in the light. This suggests that the RSC is important for path integration and incorporates visuospatial information to maintain path integration accuracy.

Distinct roles of medial and lateral entorhinal cortex in spatial cognition.

It is known that the entorhinal cortex plays a crucial role in spatial cognition in rodents. Neuroanatomical and electrophysiological data suggest that there is a functional distinction between 2 subregions within the entorhinal cortex, the medial entorhinal cortex (MEC), and the lateral entorhinal cortex (LEC). Rats with MEC or LEC lesions were trained in 2 navigation tasks requiring allothetic (water maze task) or idiothetic (path integration) information processing and 2-object exploration tasks allowing testing of spatial and nonspatial processing of intramaze objects. MEC lesions mildly affected place navigation in the water maze and produced a path integration deficit. They also altered the processing of spatial information in both exploration tasks while sparing the processing of nonspatial information. LEC lesions did not affect navigation abilities in both the water maze and the path integration tasks. They altered spatial and nonspatial processing in the object exploration task but not in the one-trial recognition task. Overall, these results indicate that the MEC is important for spatial processing and path integration. The LEC has some influence on both spatial and nonspatial processes, suggesting that the 2 kinds of information interact at the level of the EC.