The aim of this work is: 1-To explore the cognitive profile of patients with Parkinson's disease; 2-To study the role of the genetic factor in the development of cognitive impairment in Parkinson's disease; 3- To correlate cognitive impairment in Parkinson's disease with the micro-structural changes in the brain; 4-To evaluate the role of the event related potential P300 in assessment of cognitive function in Parkinson's disease.