Lesions in the basal ganglion and hippocampus on performance in a Wisconsin Card Sorting Test-like task in pigeons

Previous studies of LPO (lobus parolfactorium) and hippocampal lesions in pigeons suggest function of cognitive flexibility in LPO and memory consolidation in hippocampus [Watanabe S. Effects of hippocampal lesions on repeated acquisition of spatial discrimination in pigeons. Behav Brain Res 2001;120:59-66. [40]; Watanabe S. Effects of LPO lesions on repeated acquisition of spatial discrimination in pigeons. Brain Behav Evol 2002;58:333-342. [41]]. Here, a test similar to the Wisconsin Card Sorting Test was applied to pigeons. The test consisted of four discriminations, namely red-green color discrimination and its reversal, left-right spatial discrimination and its reversal. In each trial stimuli were presented until the correct choice occurred. Ten successive correct trials without wrong response were defined as the criterion of discrimination. When the subjects reached the criterion in one discrimination, they were trained on one of three other discrimination tasks in the next session. These four discriminations were trained repeatedly in random sequence. After the birds have been well learned the WCST-like task, their hippocampus or lobus parolfactorium (LPO), the avian basal ganglion, was damaged. A sham lesion group received anesthesia only. Both lesions impaired the WCST-like test. Lesions of the LPO increased the number of errors, while the hippocampal lesions increased the number of trials to reach the criterion only. The number of errors reflects difficulty in finding the correct stimulus or cognitive flexibility, while the number of trials reflects difficulty in stable responding or memory consolidation. The present results suggest that LPO has the function of cognitive flexibility.