Abstract
The effects of lateralization and type of motor symptom at disease onset on cognitive functioning in Parkinson's disease were examined. While previous studies have studied these factors separately, no investigation has considered the effects of these variables simultaneously. The current study proposed that patients with right-sided disease onset would show fewer cognitive changes than patients with left-sided disease onset. In addition, patients with tremor only at disease onset were predicted to have less cognitive decline than patents with bradykinesia and rigidity. Further, it was hypothesized that there would be an additive effect of lateralization and type of motor symptom at disease onset, where patients with right-sided tremor would be free from cognitive decline and patients with left-sided bradykinesia/rigidity would demonstrate the greatest cognitive impairments. Eight cognitive tasks assessing language, visuospatial, memory and executive functioning were administered to 67 patients with idiopathic PD. Patients were categorized by side of disease onset (Right-sided and Left-sided) and symptom type at disease onset (Tremor-only and Bradykinesia/Rigidity). Results indicated that patients with right-sided tremor at disease onset (RSO-T-only) performed significantly better than the other PD subgroups across the entire neuropsychological battery. Further, this PD subgroup demonstrated preservation of cognition as compared to a group of healthy control participants, while patients with right-sided bradykinesia/rigidity, left-sided-tremor, and left-sided-bradykinesia/rigidity at disease onset showed widespread deficits in cognitive functioning. No additive risk of cognitive decline was observed for patients with left-sided bradykinesia/rigidity. In sum, the present study indicates that a preservation of cognition in PD requires both a relative sparing of the tight hemisphere and the frontal subcortical circuitry underlying bradykinesia and rigidity. If either system is disrupted, neuropsychological deficits will be observed.