Ryan Jollie, Christopher I. Higginson, Ph.D., Karen A. Sigvardt, Ph.D.

The Relation Between Premorbid Occupation Level and Overall Cognitive Function in Parkinson’s Disease

Parkinson’s disease (PD) is a progressive neurodegenerative disorder characterized by both motor and cognitive symptoms. As PD has been viewed as a disease of primarily motor symptoms however, the cognitive symptoms associated with the disease have received less attention in the literature. Furthermore, few studies have addressed protective factors associated with cognitive decline in PD. Cognitive reserve (CR) is a construct in the literature which suggests that individuals acquire protective benefits which may buffer them against brain pathology and cognitive decline. Various life experiences, such as years of education or occupational attainment frequently serve as proxy measures of CR. While much research has been conducted addressing CR as it relates to cognitive decline and dementia in Alzheimer’s disease, few studies have examined its role in PD. The purpose of the current study was to examine the role that CR, as measured by occupational attainment, may play in protecting against dementia and cognitive decline in PD. It was hypothesized that those participants achieving a higher level of occupational attainment would be less likely to be diagnosed with dementia and would exhibit a higher overall level of cognitive function. Participants for the study consisted of 140 individuals with PD undergoing baseline evaluation for functional neurosurgery. As part of their evaluation, participants completed the Wechsler Adult Intelligence Scale (Third Edition). This measure was used to operationally define overall level of cognitive function. The Hollingshead index, a four-factor index of socioeconomic factors designed to measure and individual’s social status, was used to establish participants’ level of occupational attainment. Following a thorough neuropsychological evaluation, 20 participants met DSM-IV criteria for dementia. As hypothesized, individuals with higher Hollingshead scores were less likely to be diagnosed with dementia, χ²(4)=17.02, p=.002, and had higher current Full Scale IQ scores, F(4, 124)=5.93, p<.001. These results support the CR hypothesis, suggesting that CR may protect individuals from cognitive decline and dementia in PD.