Environmental complexity affects contextual fear conditioning following hippocampal lesions in rats

Rotman Research Institute, Baycrest Centre, Toronto, Canada.
Hippocampus (Impact Factor: 4.3). 05/2007; 17(5):333-7. DOI: 10.1002/hipo.20275
Source: PubMed

ABSTRACT Contextual fear conditioning has become a benchmark measure for hippocampal function, even though several studies report successful acquisition in hippocampal-damaged rodents. The current study examined whether environmental complexity may account for these discrepancies. We directly compared single-session contextual fear conditioning in rats in a simple vs. complex environment. Hippocampal lesions led to reduced fear conditioning in both contexts, as measured by freezing, but the effect was significantly greater in the complex context. As well, lesions led to generalized fear when the complex context was paired with shock, but not when the simple context was paired. We suggest that the representation of the simple context formed by rats with hippocampal lesions was adequate to support associative learning, but the representation of the complex context, which depended to a greater extent on relational learning, was not. The results were interpreted as consistent with theories of hippocampal function that emphasize its role in integrating multiple stimulus elements in a memory trace.

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Available from: Morris Moscovitch, Apr 13, 2015
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    • "However, the context itself is multifactorial and can vary in terms of the shape, colour, pattern and texture of the conditioning chamber, the shape and size of the room where training and testing occur, as well as the number and type of distal stimuli distributed in the surrounding environment and their relation to each other. As indicated above, only one study (Moses et al., 2007) has attempted to manipulate context systematically , but even that one did not investigate the effect of variation within a complex context and how it may interact with the other variables. "
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    • "Not all studies find that lesions of the hippocampus affect context conditioning (Frankland et al. 1998; McNish et al. 1997; Winocur 1997). Recent preclinical evidence indicates that context conditioning is hippocampus-dependent for complex but not simple environments (Moses et al. 2007). This is consistent with human findings demonstrating that context conditioning with unidimensional contextual stimuli fails to activate the hippocampus (Armony and Dolan 2001), while more complex spatial environments do activate the hippocampus. "
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