Evidence of contextual fear after lesions of the hippocampus: a disruption of freezing but not fear-potentiated startle.
The roles of the dorsal hippocampus and the central nucleus of the amygdala in the expression of contextual fear were assessed using two measures of conditioned fear: freezing and fear-potentiated startle. A discriminable context conditioning paradigm was developed that demonstrated both conditioned freezing and fear-potentiated startle in a context paired previously with foot shock, relative to a context in which foot shock had never been presented. Post-training lesions of the central nucleus of the amygdala completely blocked both contextual freezing and fear-potentiated startle. Post-training lesions of the dorsal hippocampus attenuated contextual freezing, consistent with previous reports in the literature; however, these same lesions had no effect on fear-potentiated startle, suggesting preserved contextual fear. These results suggest that lesions of the hippocampus disrupt the freezing response but not contextual fear itself.
McNish
K A
KA
Department of Psychiatry, Yale University School of Medicine, Connecticut Mental Health Center, New Haven, Connecticut 06508, USA.
Gewirtz
J C
JC
Davis
M
M
D000161:Acoustic Stimulation; D000679:Amygdala / Q000293:injuries / Q000502:physiology*; D000818:Animals; D001362:Avoidance Learning / Q000502:physiology*; D003214:Conditioning, Classical / Q000502:physiology*; D004556:Electric Injuries / Q000503:physiopathology; D004597:Electroshock; D005239:Fear / Q000502:physiology*; D006624:Hippocampus / Q000293:injuries / Q000502:physiology*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D013216:Reflex, Startle / Q000502:physiology*