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Behavioral/Systems/Cognitive Context Fear Learning in the Absence of the Hippocampus
 

Summary: Behavioral/Systems/Cognitive
Context Fear Learning in the Absence of the Hippocampus
Brian J. Wiltgen,1 Matthew J. Sanders,1 Stephan G. Anagnostaras,2 Jennifer R. Sage,2 and Michael S. Fanselow1
1Psychology and the Brain Research Institute, University of California, Los Angeles, Los Angeles, California 90095, and 2Psychology and Neurosciences
Program, University of California, San Diego, La Jolla, California 92093
Lesions of the rodent hippocampus invariably abolish context fear memories formed in the recent past but do not always prevent new
learning. To better understand this discrepancy, we thoroughly examined the acquisition of context fear in rats with pretraining excito-
toxic lesions of the dorsal hippocampus. In the first experiment, animals received a shock immediately after placement in the context or
aftervariabledelays.Immediateshockproducednocontextfearlearninginlesionedratsorcontrols.Incontrast,delayedshockproduced
robust context fear learning in both groups. The absence of fear with immediate shock occurs because animals need time to form a
representation of the context before shock is presented. The fact that it occurs in both sham and lesioned rats suggests that they learn
about the context in a similar manner. However, despite learning about the context in the delay condition, lesioned rats did not acquire
as much fear as controls. The second experiment showed that this lesion-induced deficit could be overcome by increasing the number of
conditioning trials. Lesioned animals learned normally after multiple shocks, regardless of freezing level or trial spacing. The last
experiment showed that animals with complete hippocampus lesions could also learn about the context, although the same lesions
produced devastating retrograde amnesia. These results demonstrate that alternative systems can acquire context fear but do so less
efficiently than the hippocampus.
Key words: amnesia; memory; conditioning; emotion; rats; spatial
Introduction
The hippocampus is essential for the acquisition and retrieval of

  

Source: Anagnostaras, Stephan - Neurosciences Program & Department of Psychology, University of California at San Diego

 

Collections: Biology and Medicine