Imprinting in the domestic chick: the role of each side of the hyperstriatum ventrale in acquisition and retention.

Abstract

Previous experiments have shown that the acquisition of a preference through imprinting is impaired if part (IMHV) of the hyperstriatum ventrale is destroyed bilaterally before chicks are exposed to a visually conspicuous (training) object. The present experiments were undertaken to determine (i) whether the acquisition of a preference for the training object is possible with only one IMHV intact and, if acquisition is possible, (ii) whether destruction of this IMHV impairs retention. Chicks were hatched and reared in darkness to congruent to 12 h posthatch. The chicks were then anaesthetised and a lesion placed in (i) the left IMHV (N = 12 chicks), (ii) the right IMHV (N = 12), (iii) the left hyperstriatum accessorium (HA) (N = 12) or (iv) the right HA (N = 12). There were 48 sham operated controls. Approximately 24 h after the operation chicks were exposed to the training stimulus. Their approach to this stimulus and to a second, novel stimulus were then measured and a preference score calculated. All five groups of chicks preferred the training stimulus and the magnitude of the preference was similar in all groups. To determine whether the IMHV region which had been intact during training was essential for retention, all chicks were anaesthetised for a second time, congruent to 20 h after the end of training. The remaining IMHV region was then destroyed. Approximately 28 h later the chicks' preferences were again measured. The sham operated and HA lesioned chicks continued strongly to prefer the training stimulus, but the birds lesioned in IMHV showed no such retention, the preference score of the IMHV chicks being significantly lower than that of the sham operated and HA lesioned chicks. The order in which the right and left sides were destroyed did not significantly influence the preference score; this result was true both for IMHV and for HA chicks.(ABSTRACT TRUNCATED AT 250 WORDS)