Learning performance on the discrimination-shift task in patients with cortical and subcortical lesions

Patients with brain damage completed reversal and nonreversal shift-learning tasks and we compared their performance with that of normal adults. The overall group differences revealed that many patients could not reach the task criterion regardless of the location of damage and the shift condition of the task. When we compared patients with subcortical and cortical damage, we also found no group differences with regard to the total number of trials required to reach the learning criterion and in terms of their learning processes during shift learning. However, when we compared patients with subcortical and unilateral cortical damage, the results revealed that the learning processes of patients with subcortical damage were normal, whereas the patients with unilateral cortical damage showed lesion-specific effects on shift learning. These findings are discussed in light of previous developmental findings and the proposed role of subcortical structures in learning.