Biomechanics | NINE Lab

Age-related Reorganization of Corticomuscular Connectivity During Locomotor Perturbations

Sun, 28 Sep 2025 00:00:00 +0000

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Abstract

Locomotor perturbations elicit cortical and muscular responses that help minimize motor errors through neural processes involving multiple brain regions. The anterior cingulate cortex monitors motor errors, the supplementary motor areas integrate sensory and executive control, and the posterior parietal cortices process sensorimotor predictions, while muscles show increased activation and co-contraction patterns. With aging, these neural control strategies shift; older adults demonstrate less flexible cortical and muscular responses, using compensatory overactivation and simpler muscle synergies to maintain performance comparable to young adults. We investigated corticomuscular connectivity patterns during perturbed recumbent stepping in seventeen young adults (age 25±4.9 years) and eleven older adults (age 68±3.6 years) using high-density EEG (128 electrodes) and EMG from six bilateral muscles. Brief mechanical perturbations (200ms of increased resistance) were applied at left or right leg extension-onset or mid-extension during continuous stepping at 60 steps per minute. We applied independent component analysis, source localization, and direct directed transfer function to quantify bidirectional information flow between cortical clusters and muscles in theta (3-8 Hz), alpha (8-13 Hz), and beta (13-35 Hz) bands. Young adults demonstrated concentrated electrocortical sources in anterior cingulate cortex, bilateral supplementary motor areas, and bilateral posterior parietal cortices, with strong theta-band synchronization following perturbations. In contrast, older adults showed fewer differentiated cortical sources, particularly lacking distinct anterior cingulate activity, and exhibited only minimal synchronization changes. Baseline corticomuscular connectivity was significantly stronger in older adults compared to young adults (p=0.012), suggesting fundamental differences in resting motor control states. During perturbations, young adults employed flexible, task-specific connectivity modulation involving error-processing networks, with the anterior cingulate showing selective bidirectional connectivity changes with specific muscles. Older adults relied on more diffuse (i.e., not focused to specific brain area) connectivity patterns dominated by motor and posterior parietal cortices, with strong connections to multiple upper and lower limb muscles simultaneously. These findings reveal an age-related strategic reorganization from dynamic, error-driven neural control to a more constrained, stability-focused approach that may reflect compensation for sensorimotor changes. The distinct connectivity signatures establish perturbed recumbent stepping as a valuable tool for assessing corticomuscular communication and provide normative benchmarks for developing targeted rehabilitation interventions to restore efficient motor control in aging and neurological populations.

Key findings: Young vs. older adult corticomuscular connectivity

Citation

@ARTICLE{Shirazi2025-cmc,
  title    = "Age-related Reorganization of Corticomuscular Connectivity During
              Locomotor Perturbations",
  author   = "Shirazi, Seyed Yahya and Tasin, Shahamat Mustavi and Huang,
              Helen J",
  journal  = "bioRxiv",
  pages    = "2025.09.28.679054",
  month    =  "28~" # sep,
  year     =  2025,
  doi      = "10.1101/2025.09.28.679054",
  language = "en"
}

Age-related Reorganization of Corticomuscular Connectivity During Locomotor Perturbations

Sat, 28 Sep 2024 00:00:00 +0000

Download

Paper
Code and data available upon request

Abstract

Key findings: Young vs. older adult corticomuscular connectivity

Citation

@ARTICLE{Shirazi2025-cmc,
  title    = "Age-related Reorganization of Corticomuscular Connectivity During
              Locomotor Perturbations",
  author   = "Shirazi, Seyed Yahya and Tasin, Shahamat Mustavi and Huang,
              Helen J",
  journal  = "bioRxiv",
  pages    = "2025.09.28.679054",
  month    =  "28~" # sep,
  year     =  2025,
  doi      = "10.1101/2025.09.28.679054",
  language = "en"
}

Older adults use fewer muscles to overcome perturbations during a seated locomotor task

Wed, 08 May 2024 00:00:00 +0000

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Abstract

Locomotor perturbations provide insights into humans response to motor errors. We investigated the differences in motor adaptation and muscle co-contraction between young and older adults during perturbed arms and legs recumbent stepping. We hypothesized that besides prolonged adaptation due to use-dependent learning, older adults would exhibit greater muscle co-contraction than young adults in response to the perturbations. Perturbations were brief increases in resistance applied during each stride at the extension-onset or mid-extension of the left or right leg. Seventeen young adults and eleven older adults completed four 10-minute perturbed stepping tasks. Subjects were instructed to follow a visual pacing cue, step smoothly, and use all their limbs to drive the stepper. Results showed that young and older adults did not decrease their errors with more perturbation experience, and errors did not wash out after perturbations were removed. Interestingly, older adults consistently had smaller motor errors than young adults in response to the perturbations. Older adults used fewer muscles to drive the stepper and had greater co-contraction than young adults. The results suggest that despite similar motor error responses, young and older adults use distinctive muscle recruitment patterns to perform the motor task. Age-related motor strategies help track motor changes across the human lifespan and are a baseline for rehabilitation and performance assessment.

Older adults use fewer muscles to overcome perturbations

Differential Theta-Band Signatures of the Anterior Cingulate and Motor Cortices During Seated Locomotor Perturbations

Thu, 04 Feb 2021 00:00:00 +0000

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Abstract

Quantifying motor and cortical responses to perturbations during seated locomotor tasks such as recumbent stepping and cycling will expand and improve the understanding of locomotor adaptation processes beyond just perturbed gait. Using a perturbed recumbent stepping protocol, we hypothesized motor errors and anterior cingulate activity would decrease with time, and perturbation timing would influence electrocortical elicitation. Young adults (n = 17) completed four 10-minute arms and legs stepping tasks, with perturbations applied at every left or right leg extension-onset or mid-extension. A random no-perturbation ``catch" stride occurred in every five perturbed strides. We instructed subjects to follow a pacing cue and to step smoothly, and we quantified temporal and spatial motor errors. We used high-density electroencephalography to estimate sources of electrocortical fluctuations shared among >70% of subjects. Temporal and spatial errors did not decrease from early to late for either perturbed or catch strides. Interestingly, spatial errors post-perturbation did not return to pre-perturbation levels, suggesting use-dependent learning occurred. Theta (3-8 Hz) synchronization in the anterior cingulate cortex and left and right supplementary motor areas (SMA) emerged near the perturbation event, and extension-onset perturbations elicited greater theta-band power than mid-extension perturbations. Even though motor errors did not adapt, anterior cingulate theta synchronization decreased from early to late perturbed strides, but only during the right-side tasks. Additionally, SMA mainly demonstrated specialized, not contralateral, lateralization. Overall, seated locomotor perturbations produced differential theta-band responses in the anterior cingulate and SMAs, suggesting that tuning perturbation parameters, e.g., timing, can potentially modify electrocortical responses.

The cortical areas active in response to mechanical perturbations during seated locomotor tasks

Citation

@INPROCEEDINGS{Shirazi2019-ke,
  title     = "Influence of Mismarking Fiducial Locations on {EEG} Source
               Estimation*",
  author    = "Shirazi, S Y and Huang, H J",
  booktitle = "2019 9th International IEEE/EMBS Conference on Neural Engineering
               (NER)",
  pages     = "377--380",
  month     =  Mar,
  year      =  2019
}