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Rob MacLennan1, Jesus Hernandez-Sarabia2, Shawn Reese1, Jocarol Shields1, Claire Smith1, Katharina Stute3, Jordyn Collyar1, Alex Olmos1, Tyler Danielson1, Demi MacLennan4, Jason Pagan5, Ryan Girts6, Kylie Harmon7, Nicholas Coker8, Joshua Carr9, Xin Ye10, Jonathan Perry11, Matt Stock5 and Jason DeFreitas1

1Oklahoma State University, Stillwater, OK

2California State University – Bakersfield, Bakersfield, CA

3Chemnitz University of Technology, Chemnitz, Germany

4The Ohio State University, Columbus, OH

5University of Central Florida, Orlando, FL

6Pfeiffer University, Misenheimer, NC

7Syracuse University, Syracuse NJ

8Springfield College, Springfield, MA

9Texas Christian University, Fort Worth, TX

10University of Hartford, West Hartford, CT

11Houston, TX

BACKGROUND: Use of functional near-infrared spectroscopy (fNIRS) to measure and image brain activity during movement is increasing. This technique uses near-infrared light to detect changes in oxygenation in the cortex which are associated with increased cortical activity. However, fNIRS is known to have lower spatial resolution than other brain imaging techniques. Due to its relatively low spatial resolution, it is unclear if fNIRS can discriminate between nearby areas of the motor cortex (M1). This capability is particularly important in studies requiring lower extremity contractions for 2 reasons: 1.) the left and right leg areas of the motor cortex are in close proximity, with only the longitudinal fissure separating them, and 2.) the cortical areas responsible for the most distal musculature descend inferiorly into the fissure, and are therefore deeper than most motor areas.

PURPOSE: To determine fNIRS’ ability to discern laterality of isolated unilateral lower body contractions.

METHODS: Thirty-five young volunteers visited the lab one time. Subjects wore a cap with an optical source over the intersection of the central sulcus and the longitudinal fissure and 2 optical detectors positioned 3 cm laterally in both directions over the left and right motor cortices. Brain activity was recorded while subjects performed sustained 15-second contractions with their right and left legs against an isometric dynamometer at 30% of their maximal force. The mean hemodynamic responses were analyzed with a 2-way (contraction type [left & right legs] × hemisphere [left & right detectors]) repeated measures ANOVA.

RESULTS: There was a significant contraction type × hemisphere interaction (p = 0.002). During right leg contractions, activity in the left hemisphere was 77% higher than activity in the right hemisphere. During left leg contractions, activity in the right hemisphere was 43% higher than activity in the left hemisphere.

CONCLUSION: The significant interaction found in this study suggests that fNIRS is capable of discerning nearby areas of the motor cortex. Further, this technology has sufficient depth of penetration and spatial resolution to identify which cortical hemisphere is active during a unilateral lower body contraction.

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