Isolation rearing from weaning has been reported to enhance excitatory cond
itioning. The present study employed a conditioned inhibition procedure to
examine whether this result was attributable to locomotor hyperactivity. Ra
ts were raised from 21 days old in isolation or in groups of five. In Phase
1, presentation of stimulus A+ was followed immediately by sucrose availab
ility (excitatory conditioning). In Phase 2, sucrose was again presented af
ter A+ alone, but not after a compound presentation of A+ with a second sti
mulus, B-. Thus, B is believed to acquire conditioned inhibitory properties
, countering the excitatory impact of A, and reducing responding specifical
ly to this stimulus compound. Isolates showed enhanced excitatory condition
ing in Phase 1. Furthermore, acquisition of conditioned inhibition in Phase
2 was also facilitated by isolation rearing. In Phase 3, B- was paired wit
h a period of sucrose availability. Isolation rearing initially retarded re
sponding to B-, confirming that this stimulus possessed a greater degree of
behavioural inhibition in these animals. Later in training, isolates showe
d enhanced excitatory conditioning to B-, as shown previously to A+ in Stag
e 1. These results suggest that isolation rearing enhances the acquisition
of appetitive Pavlovian associations, independently of locomotor hyperactiv
ity. (C) 1998 Elsevier Science Inc.