General Design and Methods The overall goal of this proposal is to validate ANAM-PD as an assessment tool for cognitive status in PD. We propose a comprehensive strategy to evaluate the sensitivity and specificity of ANAM-PD in detecting cognitive changes in patients with a diagnosis of PD (n=50) and healthy controls (n=25). The specific testing domains of the ANAM-PD battery will be validated against standardized neuropsychological testing, described in detail below. The reliability of the ANAM-PD battery will be evaluated through a test-retest procedure in a subset of 50 subjects (25 PD and 25 HC). This strategy will enable us to evaluate the individual domains of the ANAM-PD computerized cognitive test and establish a battery as a standard test to efficiently measure cognitive changes in PD. We also propose to explore functional neuroimaging of the cholinergic system using [123I] IBVM and SPECT, a marker of vesicular acetylcholine transporter and a measure of the integrity of the cholinergic neuronal system. Identifying and validating ANAM-PD as an efficient tool for assessing cognitive changes in PD and exploring the cholinergic transporter system in PD through functional neuroimaging could predict sub-sets of PD patients 'at risk' for developing dementia and help elucidate the neurochemistry related to cognitive decline in PD