The hippocampus and dorso-lateral striatum link distinct types of memories through time and space, respectively

Different kinds of memories result from the activity of distinct neural networks. In particular, memory for facts and events, known as episodic memory, depends on the integrity of the hippocampus (HPC) while habits involve a part of the basal ganglia known as the putamen in humans and dorso-lateral striatum (DSL) in rodents 1,2. Some of the strongest empirical evidence supporting this view indicates that HPC lesions impair spatial navigation, but leave intact stimulus-response (S-R) behaviors, while DSL lesions result in the opposite pattern of results. This dissociation was recently shown however to be dependent on past experience 3 4, as it does not occur when animals acquire spatial and response memories concurrently in the same environment. The current work revealed that time and space play distinct and largely complementary roles in linking different types of memories within the HPC and DSL networks. When rats learned spatial navigation and cue response concurrently but in two different contexts, HPC lesions impaired performance in both tasks while DSL lesions affected only cue response. In contrast, when a different group of rats learned the same tasks in one context but during different days, HPC affected spatial navigation only while DSL lesions impaired performance in both tasks. Lesions of the medial striatum (DSM) impaired performance in both tasks regardless of training conditions, indicating that the processes HPC and DSL networks undergo to link distinct memories are specific to these local networks. Comparison of lesion effects across experimental groups and task performance showed that normal spatial and response behaviors can have highly different underpinnings depending upon past experience. These results reveal that based on time and space, different types of memories can be integrated within specific memory networks.