Effects of lobus parolfactorius lesions on repeated acquisition of spatial discrimination in pigeons.

The basal part of the avian telencephalon can be divided into the paleostriatum augmentatum, paleostriatum primitivum and lobus parolfactorius (LPO). In the present experiments, the cognitive functions of the LPO in pigeons were examined. Pigeons were trained on spatial discrimination with or without added color cues using a repeated acquisition procedure. The discrimination task was a choice of three keys in an operant chamber. Every time the subjects reached the criterion, they were trained on a different discrimination in which one of two previously incorrect keys became the correct key. In the task with added color each key had a unique color (i.e., color discrimination). The LPO lesions disrupted the acquisition of both the spatial discrimination and the discrimination with added color. Birds with LPO damage emitted many errors in the first trial indicating the preservation of a previously correct response. Thus, the LPO lesions caused cognitive rigidity. These results are consistent with clinical observations of patients with basal ganglia disorders.