Date of Award

5-2023

Degree Type

Report

Degree Name

Master of Science (MS)

Department

Kinesiology and Health Science

Committee Chair(s)

David A. E. Bolton

Committee

David A. E. Bolton

Committee

Christopher J. Dakin

Committee

Brennan J. Thompson

Abstract

The ability to quickly step is an important strategy to avoid a fall. However, real-world settings often constrain a stepping path. Such constraints necessitate response inhibition to prevent an inappropriate step and select a new course of action to ultimately recover balance. The present study investigated neural mechanisms that underlie this ability to stop a highly automatic balance recovery step. In the field of cognitive neuroscience, response inhibition has typically been researched using focal hand reaction tasks performed by seated participants. This approach combined with neuroimaging has revealed a neural stopping network, which includes the right Inferior Frontal Gyrus (right IFG) as a key node in this network. It is unclear if the same brain-based stopping networks suppress a prepotent balance reaction since compensatory balance reactions are subcortically triggered, multi-segmental responses that are much faster than voluntary reactions. To test this, functional near-infrared spectroscopy (fNIRS) was used to measure brain activity in 21 young adults (ages 18-30) as they performed a balance recovery task that demanded rapid step suppression following postural perturbation. The hypothesis was that the right IFG would show heightened activity when suppressing an automatic balance recovery step. A lean and-release system was used to impose temporally unpredictable forward perturbations by releasing participants from a supported forward lean. For most trials (80%), participants were told to recover balance by quickly stepping forward. However, on 20% of trials at random, a high-pitch tone was played immediately after postural perturbation signaling participants to suppress a step and fully relax into a catch harness. This allowed us to target the ability to cancel an already initiated step in a balance recovery context. Average Oxygenated hemoglobin (HbO2) changes were contrasted between step and stop trials, 1-6 seconds post perturbation. A two-way repeated measures ANOVA tested for main effects with condition 4 (Step, Stop), and hemisphere (right, left) and for the interaction. Post hoc analysis was performed using paired t-test comparisons between Step and Stop trials for each channel (Bonferroni correction applied). Two-way, repeated measures ANOVA showed no significant interaction (F1, 20 = 1.212, p = 0.284) between factors and no significant main effect for hemisphere (F1, 20 = 0.282, p = 0.601). However, there was a significant main effect for condition where Stop trials produced a greater response compared to Step trials (F1, 20 = 31.617, p < 0.001). Follow-up analysis revealed a significant increase in three of the seven channels on each hemisphere. Consistent with the hypothesis, the results showed a greater prefrontal response during stopping trials, supporting the idea that executive brain networks are active when suppressing a balance recovery step. Contrary to our hypothesis, a similar increased response for stop trials was observed in both hemispheres indicating that step suppression was not limited to right IFG control, at least not as currently measured. This study demonstrates one way in which higher brain processes may help us prevent falls in complex environments where behavioral flexibility is necessary. This study also presents a novel method for assessing response inhibition in an upright postural context where rapid stepping reactions are required.

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