Background:
The corpus callosum is a part of the brain consisting of thick nerve fibers that connect the left and right hemispheres. In MS, the corpus callosum is known to become increasingly damaged as the disease progresses, consequently leading to reduced communication between the two hemispheres. When communication is affected in the brain, cognitive impairment, a symptom seen in many people living with MS, may arise. Examples of impairment resulting from reduced communication between the left and right hemispheres include problems with memory, attention, and information processing.
Communication between the hemispheres of the brain can be measured using functional near-infrared spectroscopy (fNIRS), a noninvasive and convenient way of monitoring oxygen levels in the brain. As brain activity increases, oxyhemoglobin (protein in red blood cells that carries oxygen) levels increase and deoxyhemoglobin (hemoglobin not carrying oxgyen) concentration decreases. fNIRS can thus determine how well the brain is communicating based on measuring the concentration of hemoglobin in the brain, specifically by monitoring changes in the intensity of light that is emitted by hemoglobin.
A study published in the Journal of Biomedical Optics this month has generated new information on brain activity and offers implications for measurement of coherence in the brains of individuals with MS, which could in turn determine severity and progression of the disease.
The Study:
Researchers from Calgary, including MS Society funded researcher and neurologist Dr. Luanne Metz and MS Society Doctoral Award recipient Nabeela Nathoo, conducted a study involving 15 individuals, of which eight had MS and seven did not. The study used fNIRS in order to detect how the brain communicated while the participants performed specific tasks, as well as during rest periods. The research team hypothesized that coherence between the left and right hemispheres would be lower in the MS group compared to the non-MS participants as a result of the damage to myelin.
The study began with the participants in a resting state while fNIRS data were collected for a five minute period. The participants were then given specific instructions on tapping the fingers of their right hand, as this is where their motor function originated (all participants were right-handed). They continued to tap their fingers with alternating periods of 30 seconds of rest.
Results:
The fNIRS data revealed increased oxyhemoglobin and total hemoglobin levels in all the participants during the finger tapping action tasks, which represented increased brain activity. The MS group, however, demonstrated a lesser increase than the non-MS group. The MS group also did not demonstrate any significant changes in total hemoglobin concentration. During the rest periods, no significant differences were detected between the two groups.
Comment:
Data from this study suggest that there is reduced coherence within the brain in people with MS while performing certain tasks, as demonstrated by a lesser magnitude of changes in oxyhemoglobin levels. A reduction in communication in the brain may occur due to the physical integrity of nerves being compromised in MS.
The results from this study also support the idea of fNIRS being a useful tool for detecting or measuring functional change in people with MS, as reduced communication may indicate MS progression. Previous studies using fNIRS reported similar coherence levels as found in the current study, demonstrating the reliability of the tool. The study demonstrates the promising potential of fNIRS in brain research and in clinical practice to noninvasively measure white matter damage and provide clues about the severity of disease in people with MS.
Source:
Jimenez JJ et al. Detection of reduced interhemispheric cortical communication during task execution in multiple
sclerosis patients using functional near-infrared spectroscopy. Journal of Biomedical Optics 2014 July; 19(7):
076008-1-076008-5