EEG evidence of posterior cortical disconnection in PD and related dementias.

Electroencephalogram (EEG) reactivity to eyes opening and 12-Hz photic stimulation was investigated in 14 healthy elderly subjects, 21 parkinsonian patients (PD), 7 demented parkinsonian patients (PDD), and 10 patients with Lewy body dementia (LBD) using global field synchronization (GFS). During eyes closed Theta GFS was increased in Parkinson's disease and patients and alpha1 GFS was decreased in LBD subjects. During 12-Hz intermittent photic stimulation (IPS), reactivity of posterior electrodes was decreased in PD and LBD patients. No reactivity was observed in PDD. Results are consistent with a graded posterior cortical disconnection in parkinsonian syndromes and with a model of dopamine-modulated thalamocortical interplay in visual processing.