The pattern of attentional deficits in Huntington's disease.

Different aspects of attention, e.g. phasic alertness, vigilance, divided attention, response flexibility response inhibition and intermodal integration, were investigated with a computerized test-battery in a group of 20 patients with Huntington's disease and 27 healthy controls. Huntington's disease patients are not impaired in reacting to task-contingent external stimulation in the phasic alertness task but the self-generated maintenance of attention as measured by the vigilance task, is disturbed. The simultaneous monitoring of different input-channels in the divided attention task and the ability to operate with information given to different modalities in the intermodal integration task are severely affected. The performance of Huntington's disease patients in the response flexibility task in which internal cued shifts are required, is impaired Huntington's disease patients are also impaired in reacting selectively to go/no-go stimuli in the response inhibition task. It is suggested that a number of 'higher' cognitive deficits described in Huntington's disease might, at least partly, be due to basic attentional disturbances.</p

Conditional learning is impaired in patients with cerebellar disease.

Eight patients with lesions restricted to the cerebellum were compared with a total of 25 age-matched controls on a reaction time (RT) task allowing the recording of simple and choice RTs as well as RTs to abstract visual patterns signifying the particular movement to be performed. In all conditions the actual movements required (either a left or a right button press) remained the same, but the cognitive requirements of the task varied. In the abstract patterns condition, the significance of the various patterns with regard to the required movement had to be learned by the subjects. The patients with cerebellar lesions were particularly impaired in this condition. It is concluded that the cerebellum is involved not just in the timing of movements but also in the decision process as to which movement should be performed under particular circumstances.</p

Conscious and subconscious sensorimotor synchronization : prefrontal cortex and the influence of awareness

One of the most compelling challenges for modern neuroscience is the influence of awareness on behavior. We studied prefrontal correlates of conscious and subconscious motor adjustments to changing auditory rhythms using regional cerebral blood flow measurements. At a subconscious level, movement adjustments were performed employing bilateral ventral mediofrontal cortex. Awareness of change without explicit knowledge of the nature of change led to additional ventral prefrontal and premotor but not dorsolateral prefrontal activations. Only fully conscious motor adaptations to a changing rhythmic pattern showed prominent involvement of anterior cingulate and dorsolateral prefrontal cortex. These results demonstrate that while ventral prefrontal areas may be engaged in motor adaptations performed subconsciously, only fully conscious motor control which includes motor planning will involve dorsolateral prefrontal cortex