Lesions of the ventro-medial basal ganglia impair the reinforcement but not the recall of memorized color discrimination in domestic chicks

Effects of bilateral chemical lesions of the ventro-medial basal ganglia (lobus parolfactorius, LPO) were examined in 3-9-day-old domestic chicks. In experiment-1, chicks were trained to peck at a blue bead that was associated with drops of water as a reward. Addition of passive avoidance training using a bitter yellow bead resulted in highly selective pecking between blue and yellow. LPO lesion (given 3-5 h after training) did not impair the selectivity when chicks were tested 24 h afterwards, while the novel reinforcement using a red bead was severely impaired. In experiment-2, chicks were trained in a GO/NO-GO color discrimination task with food reward. Trained chicks received bilateral LPO lesions, and they were tested 48 h afterwards for the number of pecks and latency of the first peck in each trial. The LPO lesion did not impair the recall of memorized color discrimination in tests, while the chicks were severely deficient in post-operative novel training. These results confirm that: (1) bilateral LPO ablation does not interfere with selective pecking based on the memorized color cues; but (2) it impairs reinforcement in novel training. LPO is thus supposed to be involved in acquisition, rather than execution of memorized behaviors.