Blood Oxygenation Level-Dependent Response to Multiple Grip Forces in Multiple Sclerosis: Going Beyond the Main...

Area of Science:

• Neuroscience
• Neuroimaging
• Neurology

Background:

• Central nervous system pathologies like multiple sclerosis (MS) necessitate studying functional responses beyond simple movement effects.
• The brain's primary motor cortex, specifically anterior (BA 4a) and posterior (BA 4p) areas, exhibit distinct anatomical and functional characteristics.
• Healthy volunteers show linear BOLD responses in BA 4a and nonlinear responses in BA 4p to varying grip forces (GF).

Purpose of the Study:

• To investigate alterations in blood oxygenation level dependent (BOLD) responses to grip forces (GF) in the BA 4a and BA 4p subregions of the motor cortex in individuals with MS.
• To compare functional BOLD-GF responses between healthy volunteers (HV) and MS subjects using polynomial modeling.
• To determine if higher-order BOLD-GF response analysis can uncover pathology-specific changes not evident from the main effect of movement.

Main Methods:

• Functional magnetic resonance imaging (fMRI) was used to measure BOLD responses during a dynamic motor task involving variable grip forces (GF).
• BOLD responses in BA 4a and BA 4p were modeled using polynomial expansion of applied GFs.
• Analysis included the main effect of movement (zeroth order) and higher-order polynomial terms (first to fourth order).

Main Results:

• The main effect of movement (zeroth order) showed significantly greater BOLD signal in both BA 4a and BA 4p in MS subjects compared to HV.
• Higher-order BOLD-GF responses were similar between MS subjects and HV in BA 4a.
• A marked alteration in higher-order BOLD-GF responses was observed in the BA 4p of MS subjects, correlating with disease severity.

Conclusions:

• Multiple sclerosis selectively affects regional BOLD responses to grip forces, particularly in the posterior BA 4 area (BA 4p), revealing nonlinear alterations.
• Polynomial analysis, extending beyond the main effect of movement, is crucial for uncovering these subtle, pathology-specific functional changes in MS.
• Future research should integrate fMRI with blood perfusion and nonlinear neuronal response analysis to elucidate the underlying pathophysiology.