Patients with focal lesions in the left (n = 7) and right (n = 4) prefrontal cortex were compared with controls (n = 16) in a task-switching experiment using four different, simple spatial tasks. Each of these tasks involved a left-right decision, either regarding an arrow, the word “left” or “right”, a circle position, or the direction of a moving line. We compared performance on trials that required rule switches versus rule repetitions (local switch costs) and we compared performance between blocks with bivalent stimuli (two dimensions present) and blocks with univalent stimuli (only one dimension present) to assess global switch costs. Patients with left prefrontal lesions, but not patients with right prefrontal lesions, exhibited increased costs on trials in which the relevant dimension switched (local switch costs), but also on no-switch trials with bivalent stimuli (global costs). We also assessed task-set inhibition in the form of the backward-inhibition effect [increased response times to recently abandoned tasks; Mayr, U., & Keele, S. Changing internal constraints on action: The role of backward inhibition. Journal of Experimental Psychology: General, 129, 4-26, 2000]. Although left frontal patients showed normal inhibition, right frontal patients showed no evidence for inhibition. These results suggest a neurocognitive dissociation between task-set selection and inhibition.

The brain localization of motor sequence learning was studied in normal subjects with positron emission tomography. Subjects performed a serial reaction time (SRT) task by responding to a series of stimuli that occurred at four different spatial positions. The stimulus locations were either determined randomly or according to a 6-element sequence that cycled continuously. The SRT task was performed under two conditions. With attentional interference from a secondary counting task there was no development of awareness of the sequence. Learning-related increases of cerebral blood flow were located in contralateral motor effector areas including motor cortex, supplementary motor area, and putamen, consistent with the hypothesis that nondeclarative motor learning occurs in cerebral areas that control limb movements. Additional cortical sites included the rostral prefrontal cortex and parietal cortex. The SRT learning task was then repeated with a new sequence and no attentional interference. In this condition, 7 of 12 subjects developed awareness of the sequence. Learning-related blood flow increases were present in right dorsolateral prefrontal cortex, right premotor cortex, right ventral putamen, and biparieto-occipital cortex. The right dorsolateral prefrontal and parietal areas have been previously implicated in spatial working memory and right prefrontal cortex is also implicated in retrieval tasks of verbal episodic memory. Awareness of the sequence at the end of learning was associated with greater activity in bilateral parietal, superior temporal, and right premotor cortex. Motor learning can take place in different cerebral areas, contingent on the attentional demands of the task.

This study investigated the link between cognitive processes and neural structures involved in motor control. Children identified as clumsy through clinical assessment procedures were tested on tasks involving movement timing, perceptual timing, and force control. The clumsy children were divided into two groups: those with soft neurological signs associated with cerebellar dysfunction and those with soft neurological signs associated with dysfunction of the basal ganglia. A control group of age-matched children who did not exhibit evidence of clumsiness or soft neurological signs was also tested. The results showed a double dissociation between the two groups of clumsy children and the tests of timing and force. Clumsy children with cerebellar signs were more variable when attempting to tap a series of equal intervals. They were also more variable on the time perception task, indicating a deficit in motor and perceptual timing. The clumsy children with basal ganglia signs were unimpaired on the timing tasks. However, they were more variable in controlling the amplitude of isometric force pulses. These results support the hypothesis that the control of time and force are separate components of coordination and that these computations are dependent on different neural systems.