Interdependence between dorsal and ventral hippocampus during spatial navigation

Abstract

Introduction The hippocampus is linked to the formation and retrieval of episodic memories and spatial navigation. In rats, it is an elongated structure divided into dorsal (septal) and ventral (temporal) regions paralleling the respective division in the posterior and anterior hippocampus in humans. The dorsal hippocampus has been suggested to be more important for spatial processing and the ventral to processing anxiety‐based behaviors. Far less is known regarding the degree to which these different regions interact during information processing. The anatomical connectivity suggests a flow of information between the dorsal and ventral regions; conversely, there are also commissural connections to the contralateral hippocampus. The current study examined the extent to which information from the dorsal hippocampus interacts with processing in the ipsilateral and contralateral ventral hippocampus following the acquisition of a spatial task. Methods Rats were well‐trained on a spatial reference version of the water maze, followed by muscimol inactivation of different hippocampal subregions in a within‐animal repeated design. Various combinations of bilateral, ipsilateral, and contralateral infusions were used. Results Combined dorsal and ventral inactivation produced a severe impairment in spatial performance. Inactivation of only the dorsal or ventral regions resulted in intermediate impairment with performance levels falling between controls and combined inactivation. Performance was impaired during contralateral inactivation and was almost equivalent to bilateral dorsal and ventral hippocampus inactivation, while ipsilateral inactivation resulted in little impairment. Conclusions Taken together, results indicate that for spatial processing, the hippocampus functions as a single integrated structure along the longitudinal axis.

Transient Inactivation of the Medial Prefrontal Cortex and Ventral Hippocampus Impairs Active Place Avoidance Retrieval on a Rotating Arena

“…It was found that spatial performance was also significantly impaired when silencing the whole hippocampi, and similarly impaired in bilateral dHPC and the vHPC inactivations. Ipsilateral inactivations (in one hemisphere) showed only minor impairment, but inactivation of one dHPC and the contralateral vHPC resulted in remarkable deficits, resembling bilateral inactivations ( Lee et al, 2019 ). Overall, despite the initial opinion that the vHPC is not involved in spatial learning, newer studies have shown that the vHPC is indeed needed for spatial learning and the representation of spatial memories, and together with the above-mentioned findings, it can be concluded that the whole hippocampus, acting as a unitary structure, is needed for spatial processing.…”

“…A more recent study investigated intercommunication between the dHPC and the vHPC during the MWM task learning in rats ( Lee et al, 2019 ). In this study, the activity of the hippocampi was locally inhibited by muscimol in bilateral or combined inactivations.…”

Ventral hippocampus-lateral septum circuitry promotes foraging-related memory

“…Consistent with present results, a recent study found that both the HPCd and HPCv were critical for food reward-directed spatial navigation in an obstacle-rich complex environment (47). Under certain testing conditions, spatial learning and memory in an aversive reinforcement-based water maze also requires both subregions of the HPC (48). Similarly, whole-brain analysis of blood flow in rats during retrieval of spatial memory in an aversive reinforcement-based Barnes maze task revealed increased activation in the CA1d and CA1-3v in trained animals compared with controls (49).…”

Dorsal, but not ventral, hippocampal inactivation alters deliberation in rats

“…Although MUS-V rats often had some scores that were intermediary between PBS and MUS-D rats, their overall pattern closely resembled the PBS pattern in all respects. The absence of any effect in the MUS-V condition was somewhat unexpected, given the central position of the ventral intermediate hippocampus and the interdependence between dorsal and ventral hippocampus in information processing (Lee et al, 2019) as well as its connections with the medial prefrontal cortex, a structure important for behavioral flexibility (Ragozzino et al, 1999;Hoover and Vertes, 2007). Although it is possible that more extensive inactivations could yield significant alterations of VTE behavior, they would also likely result in performance deficits, thus making it difficult to disentangle specific effects on…”