Investigations into widespread brain activity in older adults: A fNIRS study

Researchers have observed that older adults show widespread activity in the brain (in both hemispheres) when completing a working memory task, while younger adults show lateralized brain activity (to one hemisphere) for the same task. They suggest that this widespread activity may be compensatory and is used to counteract age-related cognitive decline; however, others have not found this widespread activity to be compensatory and instead suggest that it reflects neural inefficiency. The aim of this study is to examine age-related changes in brain function and its links with cognitive performance to provide further insight into whether widespread brain activity is compensatory. Bilateral frontal lobe brain activity was measured using functional near infrared spectroscopy (fNIRS, 24 channels) while 29 young (18-25 yrs), 14 middle-aged (30-55 yrs), and 30 older adult (> 65 yrs) participants performed a N-back task with increasing working memory loads. Accuracy and reaction times (RT) were compared between age-groups and between task complexity conditions. Significantly active channels reflecting more brain activity in both hemispheres were obtained using a general linear model (GLM) and contrasts between groups and across task complexity were performed. We found that as cognitive load increases, accuracy decreases, and longer RT are observed. Older adults in particular show longer RTs compared with younger adults; however, we did not observe any significant differences in overall accuracy between these two age groups. Furthermore, we confirm that older adults show more bilateral brain activity and recruit more neural resources compared with younger adults, and this can be seen across task loads. We, therefore, showed age-related differences in brain activity that were linked with cognitive performance, and thus provide support for the compensation view. In the end, this study provides valuable insight into the changes that occur in brain activity and in our cognition as we age.