ISOLATION REARING ENHANCES THE RATE OF ACQUISITION OF A DISCRIMINATIVE APPROACH TASK BUT DOES NOT AFFECT THE EFFICACY OF A CONDITIONED REWARD

Male Lister hooded rats were reared from weaning either alone (isolati on reared) or in groups of five (socially reared controls). Experiment s began at 18-weeks postweaning. Subjects were trained to associate an arbitrary stimulus with 10% sucrose reward. Trials (VT30sec) consiste d of a 5-s light stimulus (houselight off, wall lights on), followed b y a 5-s period of access to the sucrose reward. Alcove approach betwee n trials delayed the next trial by the duration of approach plus 3 s. Activity not associated directly with approach behaviour was also reco rded. Isolation rearing enhanced the rate of acquisition of the discri minative approach response. Acquisition of both conditioned approach b ehaviour during trials and conditioned avoidance between trials was mo re rapid in isolates. In general, effects were most evident early in t raining, with asymptotic performance least affected. Horizontal and ve rtical activity extraneous to approach behaviour was enhanced in isola tes during the first training session and increased further relative t o social controls after several training sessions. Subsequently, two n ovel levers were presented; a response on one lever resulted in a 0.5- s presentation of the conditioned stimulus (CS) (probability 0.5), whe reas the second lever had no programmed consequences. Sucrose reward w as not available at any time. Both groups of animals showed a preferen ce for the CS-associated lever, although rates of response by isolates were higher than social controls on both levers. The proportion of re sponses emitted upon the active lever, by comparison with the total nu mber of responses recorded upon both levers, was, however, unaffected by isolation rearing. (C) 1998 Elsevier Science Inc.