Brain volumetric correlates of memory in early Parkinson's disease

Background: Free recall memory deficits are common in Parkinson’s disease (PD), even at early stages before mild cognitive impairment or dementia. Their association with brain structural changes has not been established. Objective: We studied local gray matter volumes in relation to different memory tasks in early stage PD. Methods: Magnetic resonance images (MRI) and neuropsychological data were obtained from 28 non-demented, medicated PD patients, and 28 healthy controls. The gray matter segments of T1-weighted MRI images were analyzed using voxel-based morphometry in relation to visual and verbal memory tasks. Measures of immediate free recall, verbal learning, delayed recall and memory consolidation were obtained. A novel measure of incidental memory was included. Results: Patients and controls showed no significant group differences in local gray matter volumes. Voxel-based morphometry analyses revealed that worse performance on an incidental visual memory task was associated with smaller right parietal gray matter volume (Family-wise error corrected P = 0.002). This association was present in the PD group (corrected P = 0.005), but not in controls (corrected P > 0.99). No associations between gray matter volumes and the other memory tasks were found in either group. Conclusions: The results suggest that right parietal cortical gray matter volume is related to free recall memory deficits in early stage PD in conditions not involving an intention to memorize visual items. This preliminary finding needs to be established in further studies utilizing incidental memory tasks in PD.