Ventral hippocampus lesions and allocentric spatial memory in the radial maze: .
CIMCYC researchers Juan Manuel Jiménez Ramos and Ignacio Morón have carried out a study on how lesions in the ventral hippocampus influence allocentric spatial memory, which was recently published in the journal Behavioral Brain Research.
Although the dorsal hippocampus (DHip) is clearly implicated in spatial learning and memory, there is currently debate as to whether the ventral hippocampus (VHip) is also necessary in allocentric-based navigation tasks. To differentiate between these two subregions of the hippocampal dorsoventral axis, the researchers examined the effect of neurotoxic lesions to the DHip and VHip in different learning situations, using a four-arm plus-shaped maze.
In Experiment 1, a standard spatial reference memory task, similar to the one that is normally used in the Morris water maze, was used. The results showed an acquisition deficit in DHip-lesioned rats but perfect learning in VHip-lesioned rats.
However, Experiment 2 used a doubly marked training protocol, that is, the animals could chose between an allocentric strategy or an E-R or habit strategy when learning the spatial task. In this task, the position of the target arm was marked simultaneously by the extra and intralabyrinth stimuli. Surprisingly, in this case, both injured groups, Dhip and Vhip, showed an allocentric deficit in a probe test performed the day after the acquisition was completed.
In Experiments 3 and 4, animals with their brains still intact learned, respectively, a spatial reference memory task or a navigation task signaled by a single stimulus that required the use of a habit E-R strategy. The DHip and Vhip lesions 2 or 3 days after reaching the learning criteria generated a profound retrograde deficit in both lesioned groups, but only in terms of allocentric information.
The results of this investigation do not support a strict function heterogeneity along the hippocampal dorsoventral axis, as some authors had previously suggested. Despite the fact that both subdivisions of the hippocampus present clear differences in connectivity and gene expression, the Dhip and Vhip can still act synergistically in some processes, such as the spatial memory classically associated with Dorsal functioning, when the characteristics of the task and the conditions require it. Thus, these data are added to those obtained recently by some authors that support the existence of a functional continuum from the dorsal to the ventral hippocampus.
Full reference:
Ramos, J.M.J. & Moron, I. (2022) Ventral hippocampus lesions and allocentric spatial memory in the radial maze: Anterograde and retrograde deficits. Behavioral Brain Research, DOI: 10.1016/j.bbr.2021.113620
Researchers contact:
- Juan M.J Ramos: jmjramos@ugr.es
- Ignacio Morón: imoron@ugr.es