Evaluating the Neural Underpinnings of Motivation for Walking Exercise

Abstract

Objective: Motivation is critically important for rehabilitation, exercise, and motor performance, but its neural basis is poorly understood. Recent correlational research suggests that the dorsomedial prefrontal cortex (dmPFC) may be involved in motivation for walking activity and/or descending motor output. This study experimentally evaluated brain activity changes in periods of additional motivation during walking exercise and tested how these brain activity changes relate to self-reported exercise motivation and walking speed.

Methods: Adults without disability (N = 26; 65% women; 25 [standard deviation = 5] years old) performed a vigorous exercise experiment involving 20 trials of maximal speed overground walking. Half of the trials were randomized to include "extra-motivation" stimuli (lap timer, tracked best lap time, and verbal encouragement). Wearable near-infrared spectroscopy measured oxygenated hemoglobin responses from frontal lobe regions, including the dmPFC, primary sensorimotor, dorsolateral prefrontal, anterior prefrontal, supplementary motor, and dorsal premotor cortices.

Results: Compared with standard trials, participants walked faster during extra-motivation trials (2.43 vs 2.67 m/s; P < .0001) and had higher oxygenated hemoglobin responses in all tested brain regions, including dmPFC (+842 vs +1694 μM; P < .0001). Greater dmPFC activity was correlated with more self-determined motivation for exercise between individuals (r = 0.55; P = .004) and faster walking speed between trials (r = 0.18; P = .0002). dmPFC was the only tested brain region that showed both of these associations.

Conclusion: Simple motivational stimuli during walking exercise seem to upregulate widespread brain regions. Results suggest that dmPFC may be a key brain region linking affective signaling to motor output.

Impact: These findings provide a potential biologic basis for the benefits of motivational stimuli, elicited with clinically feasible methods during walking exercise. Future clinical studies could build on this information to develop prognostic biomarkers and test novel brain stimulation targets for enhancing exercise motivation (eg, dmPFC).

Keywords: Aerobic Exercise; Behavior Regulation; Brain; Gait; Locomotion; fNIRS.

Figure 1

Experimental setup. (A) Walking course schematic. (B) Functional near-infrared spectroscopy (fNIRS) cap setup and wire management (left) for trial performance (right). (C) Locations of fNIRS sources (red spheres) and detectors (blue spheres) are visualized on the cortical surface of the MNI152 standard brain model. Each optode is shown with its standard 10%–5% location label and source or detector number. Black squares around source numbers 3, 5, 6, 7, 10, 11, 13, and 15 show the locations of the 8 short-channel detectors. (D) Lines between specific sources and detectors represent channels that were averaged to represent each cortical region of interest. (E) Between-participant variability in the brain regions underlying the optodes was estimated by coregistering 20 individual brain magnetic resonance images from the Human Connectome Project with the 10%–5% optode locations in standard brain space, using registration constraints to mimic cap-based optode placement at 10%–5% scalp locations. Estimated brain region boundaries from all 20 individuals are shown relative to the optode locations. aPFC = anterior prefrontal cortex; DLPFC = dorsolateral prefrontal cortex; dmPFC = dorsomedial prefrontal cortex; M1S1-LL = primary sensorimotor cortex for the lower limb; PMd = dorsal premotor cortex; SMA = supplementary motor area.

Figure 2

Oxygenated hemoglobin responses (ΔHbO₂) by task condition and brain region. Bars show mean estimates, and error bars show 95% CIs for ΔHbO₂ from baseline, controlled for trial heart rate. Bottom panels show the ΔHbO₂ time series averaged across trials and participants for each task condition, with a shaded region to depict the SE across participants. aPFC = anterior prefrontal cortex; DLPFC = dorsolateral prefrontal cortex; dmPFC = dorsomedial prefrontal cortex; M1S1-LL = primary sensorimotor cortex for the lower limb; PMd = dorsal premotor cortex; SMA = supplementary motor area.