Spatial behaviour is driven by proximal cues even in mildly impaired Parkinson’s disease

This investigation addresses the question whether patients with mild to moderate Parkinson's disease (PD) show spatial deficits in real-life settings. Therefore, a "search through"-locomotor task incorporating basic features of both the radial arm maze and the Morris water maze paradigms was used. The participants had to find and remember five out of twenty hidden locations within a completely controlled environment. Different spatial memory errors and inter-response intervals were recorded automatically. Fourteen patients with idiopathic PD and fourteen healthy controls matched for age, sex, handedness, and education were investigated. Patients and controls were widely comparable with respect to intelligence, verbal memory, and executive functions. Results show that performance deteriorated in about half of the patients if the starting position was moved by 90 degrees and the proximal cues were deleted simultaneously. This deficit was systematically related to specific measures of attention. Moreover, patients were less able to update their locomotor strategies towards a more effective strategy. Results are discussed with respect to the patient's inability to generate rules which can be flexibly used in changing environments, especially if proximal cues are removed. It is concluded that deficits in spatial behaviour can be elicited even in near-to-real-life situations if appropriate testing procedures are used.