Hipocampo y conocimiento espacial en ratas

Abstract

Lesions to the hippocampal system in rats result in a profound impairment of place or locale spatial learning although other learning strategies remain unaltered. The main objective of the present study was to investigate whether the spatial knowledge preserved in the hippocampal animals can be expressed flexibly under conditions different from those of the acquisition period. Rats with neurotoxic lesions to the dorsal hippocampus and sham-operated subjects were trained to reach the goal arm in a four-arm plus-shaped maze using a constant starting arm. During the training a transparent plexiglas barrier divided the maze in two equal halves in such a way that the animals could only travel from the starting arm to the goal arm, not having access to the remaining 50% of the maze. After seven days of training, a transfer test was used in which the starting arms were the two arms from which the animals had not started during the training phase. Results indicated that the lesioned rats made significantly more errors than the control subjects. But the most interesting results revealed that the kind of error made by the lesioned animals was congruent with the turn that they had to make during the acquisition phase in order to access the goal arm (reinforced). These results suggest that when the hippocampus is damaged a preserved highly inflexible egocentric strategy is employed to solve the spatial problem.

Hippocampal lesions can enhance discrimination learning despite normal sensitivity to interference from incidental information

“…The finding that hippocampal lesions spare acquisition of egocentric spatial information is consistent with other findings in rodents (Oliveira et al,1997; DeCoteau and Kesner,2000; Ramos and Vaquero,2000; Rogers and Kesner,2006) (see also Nadel and Hardt,2004; Burgess,2008). It is typically assumed that disruption of hippocampal function spares learning of egocentric responses such as “turn left” and “turn right.” Indeed rats with hippocampal lesions (DeCoteau and Kesner,2000; Ramos and Vaquero,2000) or inactivation of the hippocampus (Packard and McGaugh,1996) show a greater reliance on egocentric responses than control rats. In the present study, however, it is not possible to tell whether the egocentric spatial learning reflected the use of egocentric responses or learning of the relative egocentric position of the cue to the mouse's body.…”

The rodent hippocampus and spatial memory: from synapses to systems

“…But without the hippocampus, spatial memories are not merely acquired more slowly, there is also evidence that they are qualitatively different from normal memories [50,55]. Indeed, hippocampus-independent place memory in the watermaze is often characterized by its inflexibility [54,56,57], and a reliance on egocentric strategies -i.e., turning in a particular direction -is sometimes indicated in plus-maze tasks [58,59]. Such findings are consistent with the idea that the brain can employ alternative strategies and neural substrates for solving certain spatial tasks after the hippocampus is removed.…”

Sex Differences in Hippocampal Long-Term Depression and the N-Methyl-DAspartate Receptor in Rats - Positive Correlation between LTD and Glun2b Subunit

“…LTP contributes to the formation of new synapses [37], while LTD may facilitate the loss of inappropriate synaptic contacts by causing synapse weakening [38] and/or prevent synaptic saturation in neural networks [39]. It has been reported that hippocampal LTD is related to memory processes requiring behavioral flexibility in spatial learning [40], and that hippocampal lesions impair behavioral flexibility [41]. Moreover, LTD-like mechanisms have been demonstrated to involve reversal learning in the Morris water maze [42].…”