Assessment of cognitive reserve using near infrared spectroscopy

Abstract

Cognitive reserve (CR) is the ability to preserve cognitive functions in the presence of brain pathology. One commonly used proxy measure of CR is IQ. In the context of Alzheimer's disease (AD), patients with higher CR show better cognitive performance relative to brain damage therefore higher CR reduces the risk of dementia. There is a strong need to develop a reliable biomarker of CR given the growing interest in understanding protective brain mechanisms in AD. Recent fMRI studies indicate that frontoparietal network may play an important role in the maintenance of cognitive reserve. The goal of this study was to measure functional connectivity (FC) of the prefrontal cortex using near infrared spectroscopy (NIRS) and to study the relationship of prefrontal FC with cognitive abilities and motoric skills.We analyzed resting state optical data recorded from prefrontal cortex in 13 healthy individuals who were also assessed by Wechsler Abbreviated Scale of Intelligence (WASI) test and the Purdue Pegboard test (PPT). For each participant, activity of each prefrontal channel was correlated with all other channels and positive correlation coefficients were Fisher-transformed and averaged over all PFC channels giving the Global Functional Connectivity (GFC) of PFC. The resulting GFC number for each individual was then correlated with the corresponding IQ (WASI full score) and the PPT scores.Prefrontal connectivity was found to positively correlate with IQ while showing the lack of or negative correlation with the Purdue Pegboard subtests. These results demonstrate that the costeffective and noninvasive NIRS technology can be used to evaluate prefrontal functional connectivity thus providing a neurophysiological measure of cognitive reserve.