[Paradoxically, animals with hippocampal lesions should theoretically be less] affected by such a shift than intact animals. In the case of conditioned fear, for example, hippocampally-lesioned rats should show greater-than-normal fear in an out-of-context test. Indeed, Nadel (1968) demonstrated this effect; rats with dorsal hippocampal lesions tested in context B for fear of a CS paired with shock in context A actually showed more fear than did control rats. This parallels observations of Penick and Solomon (1991), and is consistent with the report by Good and Honey (1991) showing that hippocampal lesions impaired rats’ ability to learn that a stimulus was reinforced in one context but not in another (see also Lehmann et al., 2005; but see Hall et al., 1996). It is also consistent with the recent findings that hippocampal inactivation impairs the context specificity of latent inhibition (Maren & Holt, 2000), and extinction (Corcoran et al., 2005; Hobin et al., 2006), and that reinstatement of conditioned fear in humans is context specific (LaBar & Phelps, 2005).

Paradoxically, animals with hippocampal lesions should be less affected by such a shift than intact animals. In the case of conditioned fear, for example, hippocampal-lesioned rats should show greater-than-normal fear in an out-of-context test. In my doctoral work (Nadel, 1968) I showed exactly this effect, but did not at that time understand what it was telling me. Rats with dorsal hippocampal lesions tested in context B for fear of a CS paired with shock in context A actually showed more fear than did control rats. This finding parallels the Penick and Solomon (1991) result noted above, and is consistent with the report by Good and Honey (1991) showing that hippocampal lesions impaired rats’ ability to learn that a stimulus was reinforced in one context but not in another (see also Lehmann et al., 2005; but see Hall et al., 1996). It is also consistent with the recent findings that hippocampal inactivation impairs the context specificity of latent inhibition (Maren and Holt, 2000), and extinction (Corcoran et al., 2005; Hobin et al., 2006), and that reinstatement of conditioned fear in humans is context specific (LaBar & Phelps, 2005).

Anmerkungen

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