Gang Seo

All Publications

• Electro-tactile modulation of muscle activation and intermuscular coordination in the human upper extremity. Scientific reports Doan, H., Tavasoli, S., Seo, G., Park, H. S., Park, H., Roh, J. 2025; 15 (1): 2559

  Abstract

  Electro-tactile stimulation (ETS) can be a promising aid in augmenting sensation for those with sensory deficits. Although applications of ETS have been explored, the impact of ETS on the underlying strategies of neuromuscular coordination remains largely unexplored. We investigated how ETS, alone or in the presence of mechano-tactile environment change, modulated the electromyogram (EMG) of individual muscles during force control and how the stimulation modulated the attributes of intermuscular coordination, assessed by muscle synergy analysis, in human upper extremities. ETS was applied to either the thumb or middle fingertip which had greater contact with the handle, grasped by the participant, and supported a target force match. EMGs were recorded from 11 arm muscles of 15 healthy participants during three-dimensional exploratory force control. EMGs were modeled as the linear combination of muscle co-activation patterns (the composition of muscle synergies) and their activation profiles. Individual arm muscle activation changed depending on the ETS location on the finger. The composition of muscle synergies was conserved, but synergy activation coefficients altered reflecting the effects of electro-tactile modulation. The mechano-tactile modulation tended to decrease the effects of ETS on the individual muscle activation and synergy activation magnitude. This study provides insights into sensory augmentation and its impact on intermuscular coordination in the human upper extremity.

  View details for DOI 10.1038/s41598-025-86342-y

  View details for PubMedID 39833302

  View details for PubMedCentralID 164312

• Modulating Inter-Muscular Coordination Patterns in the Upper Extremity Induces Changes to Inter-Muscular, Cortico-Muscular, and Cortico-Cortical Connectivity IEEE JOURNAL OF BIOMEDICAL AND HEALTH INFORMATICS Houston, M., Seo, G., Fang, F., Park, J., Park, H., Roh, J., Zhang, Y. 2024; 28 (12): 7164-7174

  Abstract

  The changes in neural drive to muscles associated with modulation of inter-muscular coordination in the upper extremity have not yet been investigated. Such information could help elucidate the neural mechanisms behind motor skill learning.Six young, neurologically healthy participants underwent a six-week training protocol to decouple two synergist elbow flexor muscles as a newly learned motor skill in the isometric force generation in upward and medial directions. Concurrent electroencephalography and surface electromyography from twelve upper extremity muscles were recorded in two conditions (As-Trained & Habitual) across two assessments (Week 0 vs. Week 6). Changes to inter-muscular connectivity (IMC), functional muscle networks, cortico-muscular connectivity (CMC), cortico-cortical connectivity (CCC) as well as functional brain network controllability (FBNC) associated with the modulation of inter-muscular coordination patterns were assessed to provide a perspective on the neural mechanisms for the newly learned motor skills.Significant decreases in elbow flexor IMC, CMC, and increases in CCC were observed. No significant changes were observed for FBNC.The results of this study suggest that modulating the inter-muscular coordination of the elbow flexor muscle synergy during isometric force generation is associated with multiple yet distinct changes in functional connectivity across the central and peripheral perspectives.Understanding the neural mechanisms of modulating inter-muscular coordination patterns can help inform motor rehabilitation regimens.

  View details for DOI 10.1109/JBHI.2024.3413080

  View details for Web of Science ID 001373825400048

  View details for PubMedID 38913515

• Lateral thinking: Neurodegeneration of the cortical cholinergic system in Alzheimer's disease. Neurobiology of disease Crockett, R. A., Casselton, C., Howard, T. M., Wilkins, K. B., Seo, G., Brontë-Stewart, H. M. 2024: 106677

  Abstract

  Atrophy of the nucleus basalis of Meynert (NBM) is an early indicator of Alzheimer's disease (AD). However, reduced integrity of the NBM white matter tracts may be more relevant for cognitive impairment and progression to dementia than NBM volume. Research is needed to compare differences in NBM volume and integrity of the lateral and medial NBM tracts across early and later stages of AD progression.187 participants were included in this study who were either healthy controls (HC; n = 50) or had early mild cognitive impairment (EMCI; n = 50), late MCI (LMCI; n = 37), or AD (n = 50). NBM volume was calculated using voxel-based morphometry and mean diffusivity (MD) of the lateral and medial NBM tracts were extracted using probabilistic tractography. Between group differences in NBM volume and tract MD were compared using linear mixed models controlling for age, sex, and either total intracranial volume or MD of a control mask, respectively. Associations between NBM volume and tract MD with executive function, memory, language, and visuospatial function were also analysed.NBM volume was smallest in AD followed by LMCI (p < 0.0001), with no difference between EMCI and HC. AD had highest MD for both tracts compared to all other groups (p < 0.001). Both MCI groups had higher lateral tract MD compared to HC (p < 0.05). Medial tract MD was higher in LMCI (p = 0.008), but not EMCI (p = 0.09) compared to HC. Higher lateral tract MD was associated with executive function (p = 0.001) and language (p = 0.02).Integrity of the lateral NBM tract is most sensitive to the earliest stages of AD and should be considered an important therapeutic target for early detection and intervention.

  View details for DOI 10.1016/j.nbd.2024.106677

  View details for PubMedID 39307400

• Lateral Thinking: Pathway Specific Neurodegeneration of the Cortical Cholinergic System in Alzheimer's Disease. medRxiv : the preprint server for health sciences Crockett, R. A., Casselton, C., Howard, T. M., Wilkins, K. B., Seo, G., Brontë-Stewart, H. M. 2024

  Abstract

  Atrophy of the nucleus basalis of Meynert (NBM) is an early indicator of Alzheimer's disease (AD). However, reduced integrity of the NBM white matter tracts may be more relevant for cognitive impairment and progression to dementia than NBM volume. Research is needed to compare differences in NBM volume and integrity of the lateral and medial NBM tracts across early and later stages of AD progression.187 participants were included in this study who were either healthy controls (HC; n=50) or had early mild cognitive impairment (EMCI; n=50), late MCI (LMCI; n=37), or AD (n=50). NBM volume was calculated using voxel-based morphometry and mean diffusivity (MD) of the lateral and medial NBM tracts were extracted using probabilistic tractography. Between group differences in NBM volume and tract MD were compared using linear mixed models controlling for age, sex, and either total intracranial volume or MD of a control mask, respectively. Associations between NBM volume and tract MD with executive function, memory, language, and visuospatial function were also analysed.NBM volume was smallest in AD followed by LMCI (p<0.0001), with no difference between EMCI and HC. AD had highest MD for both tracts compared to all other groups (p<0.001). Both MCI groups had higher lateral tract MD compared to HC (p<0.05). Medial tract MD was higher in LMCI (p=0.008), but not EMCI (p=0.09) compared to HC. Higher lateral tract MD was associated with executive function (p=0.001) and language (p=0.02).Integrity of the lateral NBM tract is most sensitive to the earliest stages of AD and should be considered an important therapeutic target for early detection and intervention.

  View details for DOI 10.1101/2024.07.16.24310492

  View details for PubMedID 39072037

  View details for PubMedCentralID PMC11275702

• Developing new intermuscular coordination patterns through an electromyographic signal-guided training in the upper extremity JOURNAL OF NEUROENGINEERING AND REHABILITATION Seo, G., Park, J., Park, H., Roh, J. 2023; 20 (1): 112

  Abstract

  Muscle synergies, computationally identified intermuscular coordination patterns, have been utilized to characterize neuromuscular control and learning in humans. However, it is unclear whether it is possible to alter the existing muscle synergies or develop new ones in an intended way through a relatively short-term motor exercise in adulthood. This study aimed to test the feasibility of expanding the repertoire of intermuscular coordination patterns through an isometric, electromyographic (EMG) signal-guided exercise in the upper extremity (UE) of neurologically intact individuals.10 participants were trained for six weeks to induce independent control of activating a pair of elbow flexor muscles that tended to be naturally co-activated in force generation. An untrained isometric force generation task was performed to assess the effect of the training on the intermuscular coordination of the trained UE. We applied a non-negative matrix factorization on the EMG signals recorded from 12 major UE muscles during the assessment to identify the muscle synergies. In addition, the performance of training tasks and the characteristics of individual muscles' activity in both time and frequency domains were quantified as the training outcomes.Typically, in two weeks of the training, participants could use newly developed muscle synergies when requested to perform new, untrained motor tasks by activating their UE muscles in the trained way. Meanwhile, their habitually expressed muscle synergies, the synergistic muscle activation groups that were used before the training, were conserved throughout the entire training period. The number of muscle synergies activated for the task performance remained the same. As the new muscle synergies were developed, the neuromotor control of the trained muscles reflected in the metrics, such as the ratio between the targeted muscles, number of matched targets, and task completion time, was improved.These findings suggest that our protocol can increase the repertoire of readily available muscle synergies and improve motor control by developing the activation of new muscle coordination patterns in healthy adults within a relatively short period. Furthermore, the study shows the potential of the isometric EMG-guided protocol as a neurorehabilitation tool for aiming motor deficits induced by abnormal intermuscular coordination after neurological disorders.This study was registered at the Clinical Research Information Service (CRiS) of the Korea National Institute of Health (KCT0005803) on 1/22/2021.

  View details for DOI 10.1186/s12984-023-01236-2

  View details for Web of Science ID 001058829200002

  View details for PubMedID 37658406

  View details for PubMedCentralID PMC10474681

• Expanding the repertoire of intermuscular coordination patterns and modulating intermuscular connectivity in stroke-affected upper extremity through electromyogram-guided training: a pilot study Seo, G., Houston, M., Portilla, M., Fang, F., Park, J., Lee, H., Li, S., Park, H., Zhang, Y., Roh, J., IEEE IEEE. 2023: 1-4

  Abstract

  Abnormal intermuscular coordination is a major stroke-induced functional motor impairment in the upper extremity (UE). Previous studies have computationally identified the abnormalities in the intermuscular coordination in the stroke-affected UE and their negative impacts on motor outputs. Therefore, targeting the aberrant muscle synergies has the potential as an effective approach for stroke rehabilitation. Recently, we verified the modifiability of the naturally expressed muscle synergies of young able-bodied adults in UE through an electromyographic (EMG) signal-guided exercise protocol. This study tested if an EMG-guided exercise will induce new muscle synergies, alter the associated intermuscular connectivity, and improve UE motor outcome in stroke-affected UE with moderate-to-severe motor impairment. The study used the six-week isometric EMG signal-guided exercise protocol that focused on independently activating two specific muscles, the biceps and brachioradialis, to develop new muscle activation groups. The study found that both the stroke and age-matched, able-bodied groups were able to develop new muscle coordination patterns through the exercise while habitual muscle activation was still available, which led to improvements in the motor control of the trained arm. In addition, the results provided preliminary evidence of increased intermuscular connectivity between targeted muscles in the beta-band frequencies for stroke patients after training, suggesting a modulation of the common neural drive. These findings suggest that our isometric exercise protocol has the potential to improve stroke survivors' performance of UE in their activities in daily lives (ADLs) and, ultimately, their quality of life through expanding their repertoire of intermuscular coordination.Clinical Relevance- This study shows the feasibility of expanding the intermuscular coordination pattern in stroke-affected UE through an isometric EMG-guided exercise which positively affects task performance and intermuscular connectivity.

  View details for DOI 10.1109/EMBC40787.2023.10341085

  View details for Web of Science ID 001133788304199

  View details for PubMedID 38083684

• Alterations in motor modules and their contribution to limitations in force control in the upper extremity after stroke FRONTIERS IN HUMAN NEUROSCIENCE Seo, G., Lee, S., Beer, R. F., Alamri, A., Wu, Y., Raghavan, P., Rymer, W. Z., Roh, J. 2022; 16: 937391

  Abstract

  The generation of isometric force at the hand can be mediated by activating a few motor modules. Stroke induces alterations in motor modules underlying steady-state isometric force generation in the human upper extremity (UE). However, how the altered motor modules impact task performance (force production) remains unclear as stroke survivors develop and converge to the three-dimensional (3D) target force. Thus, we tested whether stroke-specific motor modules would be activated from the onset of force generation and also examined how alterations in motor modules would induce changes in force representation. During 3D isometric force development, electromyographic (EMG) signals were recorded from eight major elbow and shoulder muscles in the paretic arm of 10 chronic hemispheric stroke survivors and both arms of six age-matched control participants. A non-negative matrix factorization algorithm identified motor modules in four different time windows: three "exploratory" force ramping phases (Ramps 1-3; 0-33%, 33-67%, and 67-100% of target force magnitude, respectively) and the stable force match phase (Hold). Motor module similarity and between-force coupling were examined by calculating the scalar product and Pearson correlation across the phases. To investigate the association between the end-point force representation and the activation of the motor modules, principal component analysis (PCA) and multivariate multiple linear regression analyses were applied. In addition, the force components regressed on the activation profiles of motor modules were utilized to model the feasible force direction. Both stroke and control groups developed exploratory isometric forces with a non-linear relationship between EMG and force. During the force matching, only the stroke group showed abnormal between-force coupling in medial-lateral and backward-forward and medial-lateral and downward-upward directions. In each group, the same motor modules, including the abnormal deltoid module in stroke survivors, were expressed from the beginning of force development instead of emerging during the force exploration. The PCA and the multivariate multiple linear regression analyses showed that alterations in motor modules were associated with abnormal between-force coupling and limited feasible force direction after stroke. Overall, these results suggest that alterations in intermuscular coordination contribute to the abnormal end-point force control under isometric conditions in the UE after stroke.

  View details for DOI 10.3389/fnhum.2022.937391

  View details for Web of Science ID 000838730100001

  View details for PubMedID 35967001

  View details for PubMedCentralID PMC9365968

• Myoelectric interface training enables targeted reduction in abnormal muscle co-activation JOURNAL OF NEUROENGINEERING AND REHABILITATION Seo, G., Kishta, A., Mugler, E., Slutzky, M. W., Roh, J. 2022; 19 (1): 67

  Abstract

  Abnormal patterns of muscle co-activation contribute to impaired movement after stroke. Previously, we developed a myoelectric computer interface (MyoCI) training paradigm to improve stroke-induced arm motor impairment by reducing the abnormal co-activation of arm muscle pairs. However, it is unclear to what extent the paradigm induced changes in the overall intermuscular coordination in the arm, as opposed to changing just the muscles trained with the MyoCI. This study examined the intermuscular coordination patterns of thirty-two stroke survivors who participated in 6 weeks of MyoCI training.We used non-negative matrix factorization to identify the arm muscle synergies (coordinated patterns of muscle activity) during a reaching task before and after the training. We examined the extent to which synergies changed as the training reduced motor impairment. In addition, we introduced a new synergy analysis metric, disparity index (DI), to capture the changes in the individual muscle weights within a synergy.There was no consistent pattern of change in the number of synergies across the subjects after the training. The composition of muscle synergies, calculated using a traditional synergy similarity metric, also did not change after the training. However, the disparity of muscle weights within synergies increased after the training in the participants who responded to MyoCI training-that is, the specific muscles that the MyoCI was targeting became less correlated within a synergy. This trend was not observed in participants who did not respond to the training.These findings suggest that MyoCI training reduced arm impairment by decoupling only the muscles trained while leaving other muscles relatively unaffected. This suggests that, even after injury, the nervous system is capable of motor learning on a highly fractionated level. It also suggests that MyoCI training can do what it was designed to do-enable stroke survivors to reduce abnormal co-activation in targeted muscles. Trial registration This study was registered at ClinicalTrials.gov (NCT03579992, Registered 09 July 2018-Retrospectively registered, https://clinicaltrials.gov/ct2/show/NCT03579992?term=NCT03579992&draw=2&rank=1 ).

  View details for DOI 10.1186/s12984-022-01045-z

  View details for Web of Science ID 000819792000001

  View details for PubMedID 35778757

  View details for PubMedCentralID PMC9250207

• Feasibility of inducing new intermuscular coordination patterns through an electromyographic signal-guided training in the upper extremity: a pilot study Seo, G., Park, J., Park, H., Roh, J., IEEE IEEE. 2021: 6479-6482

  Abstract

  Abnormal intermuscular coordination has been highlighted in the field of post-stroke upper extremity (UE) rehabilitation. Relatively recent studies have quantified the altered "muscle synergies", distinctive co-activation patterns of a group of muscles, which characterize the stroke-induced abnormal intermuscular coordination. Nonetheless, whether targeting the altered muscle synergy(ies) would ameliorate the stroke-induced motor impairment and improve motor function remains unknown. Our ultimate aim is to design an exercise protocol that modifies abnormal muscle synergies and improves motor function in UE after stroke. In this study, the feasibility of an electromyographic (EMG) signal-guided exercise protocol, which targeted the alteration of an elbow flexor synergy, was tested in healthy subjects. Four neurologically intact adults participated in a six-week isometric exercise to activate two major elbow flexor muscles, biceps and brachioradialis, in isolation. Participants performed an isometric reaching in a virtual three-dimensional (3D) force space to assess any potential changes in muscle synergies during the assessment at week zero, two, four, and six of the training. EMGs of 12 UE muscles and 3D forces were collected simultaneously. A non-negative matrix factorization (NMF) was applied to the EMGs to identify synergies. From the third-to-fourth week of the training, when the participants intended to use the newly learned motor skill, they were able to activate the targeted muscle pair in isolation and induce the formation of newly emerging synergistic muscle groups. As the participants practiced to expand their repertoire of intermuscular coordination patterns, their motor control of the trained UE was improved. These findings suggest that our isometric exercise protocol can potentially modulate impaired muscle coordination in a way that benefits stroke survivor's performance in activities of daily living (ADLs) and, eventually, their quality of life.

  View details for DOI 10.1109/EMBC46164.2021.9630089

  View details for Web of Science ID 000760910506022

  View details for PubMedID 34892594