Somatosensory impairment of the feet is associated with higher activation of prefrontal cortex during walking in older adults

Abstract

Background: Over-activation of prefrontal cortex during walking has been reported in older adults versus young adults. Heighted activity in prefrontal cortex suggests a shift toward an executive control strategy to control walking. A potential contributing factor is degraded functioning of pattern-generating locomotor circuits in the central nervous system that are important to walking coordination. Somatosensory information is a crucial input to these circuits, so age-related impairment of somatosensation would be expected to compromise the neural control of walking. The present study tested the hypothesis that poorer somatosensation in the feet of older adults will be associated with greater recruitment of the prefrontal cortex during walking. This study also examines the extent to which somatosensory function and prefrontal activity are associated with performance on walking and balance assessments.

Methods: Forty seven older adults (age 74.6 ± 6.8 years; 32 female) participated in walking assessments (typical walking and obstacle negotiation) and Berg Balance Test. During walking, prefrontal activity was measured with functional near infrared spectroscopy (fNIRS). Participants also underwent somatosensory testing with Semmes-Weinstein monofilaments.

Results: The primary findings is that worse somatosensory monofilament level was associated with greater prefrontal cortical activity during typical walking (r = 0.38, p = 0.008) and obstacle negotiation (r = 0.40, p = 0.006). For the obstacle negotiation task, greater prefrontal activity was associated with faster walking speed (p = 0.004). Poorer somatosensation was associated with slower typical walking speed (p = 0.07) and obstacles walking speed (p < 0.001), as well as poorer balance scores (p = 0.03).

Conclusions: The study findings are consistent with a compensation strategy of recruiting prefrontal/executive control resources to overcome loss of somatosensory input to the central nervous system. Future research should further establish the mechanisms by which somatosensory impairments are linked to the neural control and performance of walking tasks, as well as develop intervention approaches.

Keywords: Aging; Balance; Brain; Gait; Sensory.

Figure 1.. Walking course and fNIRS setup.

A) The course is shown set up with foam obstacles for the Obstacles walking task. The orange cones marked the corners of the rectangular walking course, and participants were instructed to walk just outside the cones.Walking speed was determined with a stopwatch over a 4 meter distance within the straight portion of each lap. B) fNIRS was recorded

Figure 2.. Somatosensory monofilament level versus prefrontal oxygenated hemoglobin concentration (ΔO2Hb).

A significant associated was observed between worse somatosensation (higher level) and greater prefrontal cortical activity during the Typical walking task (panel A, r=0.38, p=0.008) and Obstacles walking task (panel B, r=0.40, p=0.006). Triangles indicate participants who report being under the care of a physician for diabetes.