The extended hippocampal-diencephalic memory system: enriched housing promotes recovery of the flexible use of spatial representations after anterior thalamic lesions

The anterior thalamic (AT) nuclei constitute an important component of an extended hippocampal-diencephalic system, and severe persisting memory deficits are normally found after AT damage. This study examined whether postoperative enrichment promotes the recovery of the flexible use of spatial representations in rats with AT lesions. After training to swim from a single constant start position to a submerged platform in a Morris water maze, rats with AT lesions that were housed in standard cages (AT-Std) performed poorly when required to swim to the platform from novel start positions during probe trials. By contrast, rats with AT lesions but housed in enriched environments (AT-Enr), like sham-lesion rats, showed relatively little disruption when tested with novel start positions. AT-Std rats also initially showed impaired acquisition of the task, whereas AT-Enr rats learned at a similar rate to that of the Sham-Std group. Beneficial effects of enrichment were replicated in the subsequent standard water maze procedure that used varying start positions throughout training to acquire a new platform location. Although it is clear that AT damage can severely disrupt episodic-like memory processes, and appear to be a core part of the interlinked neural systems subserving episodic memory, the current findings strongly encourage study on the adaptive response of the brain to thalamic lesions and prospects for the development of rehabilitation programs in cases of anterograde amnesia associated with diencephalic injury.