Impaired somatosensory discrimination of shape in Parkinson's disease: association with caudate nucleus dopaminergic function.

Tactile discrimination of macrogeometric objects in a two-alternative forced-choice procedure represents a demanding task involving somatosensory pathways and higher cognitive processing. The objects for somatosensory discrimination, i.e., rectangular parallelepipeds differing only in oblongness, were presented in sequential pairs to normal volunteers and 12 parkinsonian patients. The performance of patients was significantly impaired compared to normal volunteers. From a biochemical point of view, the patients were characterized by a severely reduced 6-[18F]-fluoro-L-dopa (FDOPA) tracer metabolism in the basal ganglia, as measured using positron emission tomography (PET). Furthermore, reduced specific FDOPA metabolism in the putamen was consistent with the impaired motor capacities of the patients. The reduced specific FDOPA-uptake within the caudate nucleus was associated with additionally diminished somatosensory discrimination. This association, of low perception during task performance and decreased FDOPA-uptake, provides direct evidence for the role of the caudate nucleus in the cognitive part of the task. We suggest that directed attention and working memory were critically involved as a result of disturbed interactions between the head of the caudate nucleus and the dorsolateral prefrontal cortex. Furthermore, there were indications of an additional involvement of the mesolimbic system, which might be of importance during challenging situations such as forced choice. We conclude that differential effects on parts of the basal ganglia, during evolution of the degenerative process characteristic of Parkinson's disease, have profound consequences on the performance of skills, as shown here for a somatosensory discrimination task.

Partial epileptic seizure with versive movements examined by [99m Tc] HM-PAO brain single photon emission computed tomography: an early post study analyzed by computerized brain atlas methods.

The consecutive steps of a seizure with leftward versive movements of the head and eyes were analyzed after video monitoring and correlated with findings on single photon emission computed tomography (SPECT) using [99m Tc] hexamethyl propylene amine oxime (HM-PAO). Evaluation included reconstruction of subtraction images from the early postictal state, obtained immediately after the video-monitored seizure, and the interictal baseline. Based on normalized perfusion indexes within voxels of Talairach space, we concluded that the primary epileptogenic focus was in the premotor cortex of the contralateral hemisphere. We then placed the functional data in an anatomic context by adapting a dedicated computerized brain atlas (CBA) to the patient's brain with the aid of magnetic resonance imaging (MRI) slices. By inverse transformation, the patient's data were aligned with the standard geometry of the brain atlas for comparison purposes with data from the literature. The validated activation field projected exactly onto the right precentral sulcus with the anterior border zone including the right frontal eye field.