The control of conditioned fear behaviour by a conditional stimulus (C
S) and contextual stimuli (CXT) was compared in rats with lesions to t
he hippocampus (HPC) or neocortex (GO), and operated controls (OC). Af
ter classical fear conditioning in a distinctive context, rats were su
bsequently tested in the presence of the CS and CXT (CS + CXT), the CS
alone (CS-only), or context alone (CXT-only). Two experiments were co
nducted in which conditioned fear was measured by an active avoidance
response (experiment 1) or by response suppression (experiment 2). Gro
ups did not differ in acquiring the conditioned fear response, as meas
ured in the CS + CON test but, in both experiments, hippocampal (HPC)
groups exhibited more conditioned fear behaviour than controls in the
CXT-Only and CS-Only conditions. It was suggested that control rats co
nditioned the fear response to a stimulus complex that incorporated th
e CS and CTX. Rats with HPC lesions did not form this association betw
een the stimulus elements; instead they segregated the CS and CXT and
formed independent associations between the conditioned response (CR)
and each component. In showing that HPC damage disrupts the process of
forming associations between environmental stimuli and that the effec
t is not restricted to contextual cues, the results help to resolve ap
parently contradictory findings regarding the role of HPC in contextua
l information processing. (C) 1997 Elsevier Science B.V.