Spatial learning impairment parallels the magnitude of dorsal hippocampal lesions, but is hardly present following ventral lesions

Abstract

The hippocampus plays an essential role in spatial learning. To investigate whether the whole structure is equally important, we compared the effects of variously sized and localized hippocampal aspiration lesions on spatial learning in a Morris water maze. The volume of all hippocampal lesions was determined. Dorsal hippocampal lesions consistently impaired spatial learning more than equally large ventral lesions. The dorsal lesions had to be larger than 20% of the total hippocampal volume to prolong final escape latencies. The acquisition rate and precision on a probe test without platform were sensitive to even smaller dorsal lesions. The degree of impairment correlated with the lesion volume. In contrast, the lesions of the ventral half of the hippocampus spared both the rate and the precision of learning unless nearly all of the ventral half was removed. There was no significant effect of the location (dorsal or ventral) of damage to the overlying neocortex only. In conclusion, the dorsal half of the hippocampus appears more important for spatial learning than the ventral half. The spatial learning ability seems related to the amount of damaged dorsal hippocampal tissue, with a threshold at about 20% of the total hippocampal volume, under which normal learning can occur.

Class I histone deacetylase inhibition ameliorates social cognition and cell adhesion molecule plasticity deficits in a rodent model of autism spectrum disorder

“…We found naïve animals to be readily capable of detecting biological motion, as has been demonstrated previously for rodents (MacKinnon et al, 2010), however the VPA-exposed animals were found to be significantly impaired in this aspect of social perception. These deficits were also associated with impairments in the water maze paradigm which further indicated that dorsal stream processing was dysfunctional in these animals as spatial learning is reliant on the more dorsal region of the hippocampus (Moser et al, 1993), an area that primarily receives afferents from sensory neocortical regions (Witter and Moser, 2006). Collectively, these observations suggest that prior in utero exposure to VPA results in the ontogenetic emergence of a significantly compromised cognitive system that is crucial to normal social behaviour in the adult animal.…”

“…As the biological motion deficits associated with ASD have been suggested to reflect a more widespread dysfunction within the dorsal stream of cognitive processing (Spencer et al, 2000;Milne et al, 2005), we determined if animals with prior in utero exposure to VPA were impaired in spatial learning as this function is dependent on the dorsal aspect of the hippocampus (Moser et al, 1993;Maguire et al, 2000). All experimental groups employed readily acquired the position of the hidden platform during the training phase of the water-maze paradigm (F[3,617]=94.00; p<0.001, twoway ANOVA).…”

Phospholipase C-β1 knockout mice exhibit endophenotypes modeling schizophrenia which are rescued by environmental enrichment and clozapine administration

“…Environmental enrichment had a positive effect upon the motor and sensorimotor behavior of the mutant mice, but did not exert a beneficial effect upon their MWM performance, a dissociation which may suggest that the aberrant phenotype caused by the PLC-b1 null mutation is mediated by distinct pathways differentially responsive to the effects of enrichment. Alternatively, given the dissociation we observe in the effects of environmental enrichment, it is of significant interest that learning and memory are particularly susceptible to dorsal hippocampal manipulations, 42,43 while locomotor activity and PPI, which are modulated, but not mediated, by the hippocampus (in that its involvement is not critical to performance of the behavior), have been shown to be much more susceptible to ventral hippocampal lesions. 44 Environmental enrichment may be regionally specific, providing another potential explanation for the discrepancy in the enrichment effect; however, further experiments would be required in order to resolve this question.…”

Isolation rearing in the rat disrupts the hippocampal response to stress

“…Isolationreared rats had signi¢cantly higher neuronal activity in vCA1 prior to stress but demonstrated a tendency for lower activity when exposed to stress while the opposite occurred in the CA2 region and dentate gyrus of the dorsal hippocampus. Moser et al (1993Moser et al ( , 1995 reported that damage to the dorsal hippocampus resulted in impairment to spatial memory, but this impairment was not found with ventral hippocampal damage. Moreover, Gentsch et al (1999) lesioned the neonatal ventral hippocampus with ibotenic acid while leaving the adjacent areas intact and reported impairment in latent inhibition.…”