Abstract
Previous studies on the role of prefronto-striatal loop systems for cognitive procedural learning (PL) brought inconsistent results. To examine whether the integrity of the dorsolateral prefrontal loop is indispensable for normal cognitive PL, we examined the acquisition of cognitive skills in 35 patients with focal prefrontal lesions, focal caudate lesions, and Huntington's Disease (HD), and compared it with a control group. To examine the potential role of the processing demands made by the cognitive tasks, a set of tasks was applied whose acquisition places demand either on reasoning and problem solving, or on the establishment of fast and repetitive processing routines. The Pursuit Rotor task was also studied with the aim to re-examine earlier findings of a functional segregation of motor and complex prefronto-striatal loops. Deficits of cognitive and motor PL were found to be limited to certain tasks and groups. PL of one task, which demanded rapid, repetitive processing of visuo-spatial stimuli, was impaired in all patient groups. PL of two problem-solving tasks was impaired in patients with focal and degenerative caudate lesions only. None of the groups was impaired at PL of Mirror Reading, another task demanding rapid and repetitive visuo-spatial processing, and none was impaired in a fifth task of language skill. Deficits of motor learning were only observed in patients in whom the motor loop was affected. These results suggest that the dorsolateral prefronto-striatal loop is involved in the establishment of cognitive processing routines. The comparison of patients with and without caudate lesions suggests that disconnection of this circuit is critical. However, the normal acquisition of two cognitive tasks even in this group indicates that the integrity of the dorsolateral prefrontal loop is not mandatory for normal cognitive PL. We discuss these dissociations with regard to the demand profiles of the applied tasks and the locations of the lesions.