Investigation of functional near-infrared spectroscopy as a monitoring tool for measuring the effect of transcranial alternating current stimulation on dementia patients’ cognitive function
Loading...
Date
2024-07-17
Authors
Azarbarzin, Samaneh
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Functional near-infrared spectroscopy (fNIRS) is used as a non-invasive neuroimaging
technique for studying the neural dynamics within the human brain. This study uses fNIRS to
explore how transcranial alternating current stimulation (tACS) affects cognitive function in
people with dementia including Alzheimer’s disease (AD). By measuring changes in blood
oxygenation levels, fNIRS provides a valuable means to capture plausible post-treatment
alterations in cerebral hemodynamics. Previous studies have shown individuals with dementia
exhibit increased oxygen consumption during verbal fluency tasks. This suggested that they might
require greater effort to compensate for cognitive deficits. Therefore, it is hypothesized that tACS
intervention will potentially alleviate this increased oxygen consumption by enhancing cognitive
function, resulting in reduced oxyhemoglobin level post-treatment amongst those who respond
positively to tACS treatment. To investigate this hypothesis, this research involved a
comprehensive examination of 29 individuals with dementia, who received both real (40 Hz) and
sham tACS treatment in a double-blind cross-over randomized trial. Each tACS intervention was
paired with cognitive exercises (CE) on a daily basis in two 30-minute sessions for four
consecutive weeks (excluding weekends) (tACS+CE). To reduce treatment effects between
intervention, each participant had a 2-5 month wash-out period between treatments. Study
participants were assigned into two groups using their age and cognitive level as the stratification
parameters. One group received real tACS first and sham second (R1S2), and the other group’s
real/sham assignment was the opposite (S1R2). An eight-channel fNIRS device was utilized to
measure blood oxygenation levels in the prefrontal cortex (PFC) before and after each treatment
block, during a mental task (word production and subtraction tasks). The results of this work are
in support of our hypothesis that patients with dementia showed a decrease in oxyhemoglobin level
after real tACS+CE by a mean difference of 0.06µM for word production task, and a significant
decrease of 0.10µM for subtraction task (p=0.04). Notably, real tACS treatment showed a higher
decrease in oxyhemoglobin levels compared to the sham treatment, suggesting that real stimulation
has a more significant impact on hemodynamic responses than only cognitive exercises. Analyzing
changes in blood oxygenation separately for group R1S2 and group S1R2 showed a significant
decrease in oxyhemoglobin levels in group R1S2 during real tACS intervention in the subtraction
task (p=0.03) but not significant for the word production task. This may be attributed to the fact
that dementia participants usually have a ceiling effect in word production task.
Description
Keywords
Functional Near-Infrared Spectroscopy(fNIRS), Transcranial Alternating Current Stimulation(tACS), Cognitive Exercise, Alzheimer' Disease, Blood Oxygenation