Lateralized cognitive functions in Parkinson's patients: A behavioral approach for the early detection of sustained attention deficits

Parkinson's disease (PD) has been described as a disconnection syndrome. The lateralized motor onset of symptoms indicates asymmetrical dysregulation of the dopamine production in the substantia nigra, in the striatum and, in turns, a dysfunction of the basal ganglia and of the connected cortical areas. However, lateralization of cognitive symptoms is less clear, and it would be important to determine whether lateralized motor deficits are associated with cognitive impairments typically documented following damage to one specific hemisphere. We tested twenty-two PD patients at various stages of the disease on a sustained attention task, namely a multiple object tracking (MOT). This task is particularly sensitive at revealing lateralized deficits, and is often used to diagnose visual field attentional deficits in stroke patients with unilateral parietal lesions. In the present study, PD patients were asked to track four moving discs (two in the left and two in the right hemifield) amidst moving distracters. Left and right visual field tracking accuracy was psychophysically measured and compared to that of age-matched controls. Results revealed distinct behaviors: left (motor deficit) PD patients showed impaired performance in the left, while right (motor deficit) PD patients were impaired in the right hemifield. Data indicate that PD affects motor as well as attentional functions. Interestingly, performance correlated with scores on the Montreal Cognitive Assessment (MoCA) a measure of cognitive functioning. Crucially, results suggest that cognitive skills might be affected as early as motor functions, and that early evaluation might be key to predicting disease progression and planning interventions.