Slowing of EEG correlates with CSF biomarkers and reduced cognitive speed in elderly with normal cognition over 4 years.

BACKGROUND: Cerebrospinal fluid (CSF) biomarkers and quantitative EEG show particular patterns of change in Alzheimer's disease (AD) and reflect neuropathologic processes and cerebral function, respectively. The changes precede cognitive decline and should be visible already in preclinical stages. We therefore aimed to investigate their relationship in cognitively healthy individuals.
METHOD: Thirty-three (33) elderly individuals with repeated normal scores on cognitive tests over 4.5 years underwent EEG recording with quantitative frequency analysis and analysis of CSF total tau (T-tau), phosphorylated tau (P-tau) and beta-amyloid(1-42) (Abeta42).
RESULTS: CSF T-tau and P-tau correlated with relative EEG theta power (r(s)>0.545; p<0.01), but not with relative alpha, beta or delta power. The combined P-tau/Abeta42 ratio exhibited an even stronger correlation with relative theta power (r(s)=0.622; p<0.001), especially in the right posterior quadrant of the head (r(s)=0.643; p<10(-4)). Slowing of cognitive speed correlated with increased relative theta power, foremost in the posterior quadrants (r(s)>0.503; p<0.01), and high P-tau/Abeta42 ratio (r(s)>0.462; p<0.01).
CONCLUSIONS: Our results suggest that already in cognitively healthy elderly subjects, biochemical changes in CSF, and the possible underlying neuropathologic processes it reflects, have an effect on cerebral function as visualized by the EEG rhythm and cognitive speed. It hereby suggests that CSF biomarkers and EEG theta activity might indicate early abnormal degenerative changes in the brain.