Spatial learning deficits in Parkinson's disease with and without mild cognitive impairment

Several MRI studies have demonstrated hippocampal atrophy in Parkinson's disease (PD), a structure considered a key element in spatial learning. Despite this, no study has been undertaken to investigate spatial navigation in PD using a virtual version of the Morris water maze, which is the gold standard for testing hippocampal function in rodents.

We studied 17 cognitively unimpaired PD patients, 12 PD patients with mild cognitive impairment (MCI) and 15 controls in a virtual water maze procedure.

Measured by the main outcome parameters latency to locate the target and heading error (average difference between direction of movement toward anticipated target and real direction toward the target), controls performed significantly better on the virtual water maze task than cognitively unimpaired PD patients or PD patients with MCI, while there was no significant difference between latter two groups.

The virtual water maze test differentiates PD patients from controls, but does not distinguish between cognitively normal and cognitively impaired PD patients, indicating a possible dopamine dependent component in spatial learning. Spatial performance deficits might thus constitute very early signs of dopamine depletion independent of the presence of MCI in Parkinson's disease.