Dementia in Parkinson disease (PD) is associated with abnormal accumulation of proteins, including β-amyloid, in cortical regions. High cognitive reserve capacity may protect cognition from β-amyloid and delay the onset of dementia. We tested the cognitive reserve theory in PD by determining whether educational attainment, a proxy for cognitive reserve, modifies the correlation between cortical β-amyloid accumulation and cognitive impairment.
PD participants (N = 155) underwent MRI to quantify brain volume and [(11)C] PiB PET imaging to quantify fibrillar β-amyloid deposition. Mean cortical binding potentials (MCBP) were calculated for each participant, with higher scores indicating more fibrillar β-amyloid. Global cognitive function was assessed using the Clinical Dementia Rating (CDR) and Mini-Mental State Examination (MMSE). Multiple linear regression analysis was used to determine whether education modified the relationship between MCBP and cognitive function after controlling for brain volume.
MCBP interacted with educational attainment to predict scores on each of the cognitive outcome measures (ps ≤ 0.02). Post-hoc analysis revealed that the effect of MCBP on cognitive function changed once the level of education reached 16 years. For participants with less than 16 years of education (n = 68), higher MCBP correlated with worse cognitive function, with MCBP accounting for 8-30% of the variance in MMSE and CDR scores (ps ≤ 0.02). For participants with at least 16 years of education (n = 87), MCBP did not correlate with MMSE or CDR scores (R(2)s < 0.02, ps ≥ 0.17).
These findings provide support for the cognitive reserve theory in PD and suggest that education may protect PD patients' cognition against cortical β-amyloid pathology.