Unilateral pallidotomy in PD: a controlled study of cognitive and behavioral effects. The Netherlands Pallidotomy Study (NEPAS) group.

OBJECTIVE: To investigate whether unilateral pallidotomy affects cognitive and behavioral functioning. METHODS: At baseline and after 6 months we assessed neuropsychological functioning in 35 patients with advanced PD. After baseline examination, patients were randomized to pallidotomy within 1 month (6 left-sided, 13 right-sided) or to pallidotomy after follow-up assessment 6 months later (n = 16; control group). We performed neuropsychological tests of language, visuospatial function, memory, attention, and executive functions. Self ratings and proxy ratings of memory problems and dysexecutive symptoms were also collected. RESULTS: No significant differences over time were found between pallidotomy and control groups, with the exception of a decrease of verbal fluency in the left-sided pallidotomy group. CONCLUSIONS: Unilateral pallidotomy is relatively safe with respect to cognition and behavior. Left-sided pallidotomy may lead to minor deterioration in verbal fluency. The sample size of this study is too small, however, to rule out the possibility of infrequent but clinically important side effects.

Disturbed frontal regulation of attention in Parkinson's disease.

Parkinson's disease is characterized not only by tremor, akinesia and rigidity, but also by frontal cognitive dysfunction, that can be understood as a disturbance in the 'Supervisory Attentional System' (SAS). This concept refers to a system, located in the frontal cortex, that regulates attentional processes under novel, non-routine conditions. The hypothesis that cognitive dysfunction in Parkinson's disease results from a disturbance in the SAS was investigated by recording 'processing negativity' in 33 parkinsonian patients and 17 controls. Processing negativity is an event-related potential that reflects neuronal activity during selective attention. The contribution of the frontal cortex to selective attention can be studied directly using processing negativity. Parkinsonian patients were also scored for clinical symptoms and subjected to a neuropsychological test battery. Processing negativity was clearly disturbed in the parkinsonian patients. Moreover, parkinsonian patients with the lowest scores on 'frontal' neuropsychological tests such as Stroop, Trail Making and Word Fluency, also had the lowest processing negativity. Our results support the hypothesis that cognitive dysfunction in Parkinson's disease might be understood as a disturbance in the frontal regulation of attentional processes. Degeneration of the dopaminergic mesocortical innervation of the frontal cortex in Parkinson's disease is a possible neurochemical substrate of these frontal attentional disturbances.