Environmental complexity affects contextual fear conditioning following hippocampal lesions in rats

Rotman Research Institute, Baycrest Centre, Toronto, Canada.
Hippocampus (Impact Factor: 4.16). 05/2007; 17(5):333-7. DOI: 10.1002/hipo.20275
Source: PubMed


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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    ABSTRACT: This review evaluates three current theories - Standard Consolidation (Squire & Wixted, 2011), Overshadowing (Sutherland, Sparks, & Lehmann, 2010), and Multiple Trace- Transformation (Winocur, Moscovitch, & Bontempi, 2010a) - in terms of their ability to account for the role of the hippocampus in recent and remote memory in animals. Evidence, based on consistent findings from tests of spatial memory and memory for acquired food preferences, favours the transformation account, but this conclusion is undermined by inconsistent results from studies that measured contextual fear memory, probably the most commonly used test of hippocampal involvement in anterograde and retrograde memory. Resolution of this issue may depend on exercising greater control over critical factors (e.g., contextual environment, amount of pre-exposure to the conditioning chamber, the number and distribution of foot-shocks) that can affect the representation of the memory shortly after learning and over the long-term. Research strategies aimed at characterizing the neural basis of long-term consolidation/transformation, as well as other outstanding issues are discussed.
    Neurobiology of Learning and Memory 10/2013; 106. DOI:10.1016/j.nlm.2013.10.001 · 3.65 Impact Factor
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    • "The findings reviewed above indicate that the hippocampus is engaged when multiple, distinct elements must be integrated or associated (Hannula et al., 2006; Olson et al., 2006b; Moses et al., 2007). This occurs readily for novel visual materials (e.g., Ezzyat and Olson, 2008; Rose et al., 2012) but is typically not required for familiar verbal materials, which can be maintained through subvocal rehearsal (a process which is supported by a network of extra-hippocampal cortical regions; Buchsbaum et al., 2005). "
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    ABSTRACT: It has been well established that the hippocampus plays a pivotal role in explicit long-term recognition memory. However, findings from amnesia, lesion and recording studies with non-human animals, eye-movement recording studies, and functional neuroimaging have recently converged upon a similar message: the functional reach of the hippocampus extends far beyond explicit recognition memory. Damage to the hippocampus affects performance on a number of cognitive tasks including recognition memory after short and long delays and visual discrimination. Additionally, with the advent of neuroimaging techniques that have fine spatial and temporal resolution, findings have emerged that show the elicitation of hippocampal responses within the first few 100 ms of stimulus/task onset. These responses occur for novel and previously viewed information during a time when perceptual processing is traditionally thought to occur, and long before overt recognition responses are made. We propose that the hippocampus is obligatorily involved in the binding of disparate elements across both space and time, and in the comparison of such relational memory representations. Furthermore, the hippocampus supports relational binding and comparison with or without conscious awareness for the relational representations that are formed, retrieved and/or compared. It is by virtue of these basic binding and comparison functions that the reach of the hippocampus extends beyond long-term recognition memory and underlies task performance in multiple cognitive domains.
    Frontiers in Human Neuroscience 05/2012; 6:146. DOI:10.3389/fnhum.2012.00146 · 2.99 Impact Factor
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    • "Different contextual factors, such as whether the tobacco stimulus depicts cigarettes from the beginning or the end of smoking (Mucha et al. 2008; Winkler et al. 2010), or whether smokers are at that moment motivated to quit smoking or not (Dempsey et al. 2007), may modulate reactivity to smoking cues suppressing or even reversing the physiological response. Evidence of context effects in nonhuman animals is relatively extensive (Moses et al. 2007; Walker and Davis 2002; Siegel and Ramos 2002). However, research on context effects in humans is still in its infancy (Grillon 2008). "
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    ABSTRACT: Cue reactivity and startle reflex modulation paradigms have been used in addiction research to determine the affective motivational state of craving induced by viewing drug-related cues. However, recent studies suggest that cue reactivity and startle reflex modulation in people with addictions can be suppressed, or even reversed, depending on context. The present study looked at the contextual specificity of smoking cue startle modulation by examining individuals with low and high motivation to quit smoking. Emotional modulation of the startle reflex was examined in 32 female smokers exposed to affective stimuli and tobacco cues. The sample was divided into high and low motivation to quit smoking groups using the Processes of Change Questionnaire. The tobacco cues produced a greater startle magnitude in the group with high motivation to quit smoking than the group with low motivation, which was independent of craving level. Motivation to be abstinent is a relevant contextual factor accounting for variance in cue reactivity in individual smokers.
    Psychopharmacology 05/2011; 218(3):525-32. DOI:10.1007/s00213-011-2334-0 · 3.88 Impact Factor
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