Biology subjects

Acosta, A. M.

Publications and source records attributed to Acosta, A. M..

4 recordsLinked to original sources

bioRxiv2026

Whole-brain precision functional mapping of a proximal upper-extremity motor task

Upper-extremity motor control has been widely studied with hand-task functional magnetic resonance imaging (fMRI) in healthy and disease states. However, proximal-arm motor tasks, such as at the shoulder, are uncommon during fMRI due to practical limitations, though they are critical to a complete understanding of upper-extremity motor control. Previous fMRI studies of proximal upper-extremity control have generally used unconstrained movements or a single low force or torque condition, leaving unknown how distributed supraspinal brain activity scales with increasing proximal motor output. Here, we implemented a custom, MR-safe device to test supraspinal brain activity during three levels of isometric shoulder abduction in healthy individuals using a whole-brain fMRI acquisition. We conducted subject-specific analysis with repeated sampling of the controlled shoulder abduction task within each individual (i.e., "precision mapping"), as the exact localization of shoulder motor activity is relatively understudied. Our analysis showed spatial variability in subject-specific motor activation compared to group-level localization. We found that shoulder abduction had a significant effect on motor activity in the primary motor cortex, supplementary motor area, dorsal premotor area, thalamus, putamen, and cerebellum. Across repeated fMRI runs, amplitude of motor activity was consistent across all tested regions. Overall, these findings provide an individualized, whole-brain torque-response characterization of the proximal upper-extremity motor system and establish an approach for examining how distributed supraspinal motor networks are recruited as mechanical demand increases. These whole-brain, subject-specific methods can be a critical tool for probing motor dysfunction in clinical populations.

neuroscience↗

bioRxiv2026

Quantifying the Effect of Trunk Postural Control on Reaching with Progressive Shoulder Abduction Loading in Hemiparetic Stroke

Background: Adults post hemiparetic stroke exhibit motor deficits in both the trunk and arm that impact function. In the paretic arm, involuntary coupling of torques in the fingers, wrist, and elbow during shoulder abduction, known as the flexion synergy, reduces reaching function. While there have been deficits shown to exist at the trunk such as weakness and altered coordination, it remains unclear if active trunk control compounds reaching deficits. This study examined if active trunk control with progressive shoulder abduction loading impacts reaching function in stroke and control participants. Methods: Thirteen adults, 9 post hemiparetic stroke (64.11 {+/-} 6.57 years) and 4 age matched controls (66.25 {+/-} 0.96 years), completed seated reaching tasks with the trunk restrained and unrestrained while reaching with their arm coupled to the ACT-3D robotic device on a frictionless table, lifting against 25% MVT, and 50% MVT. A linear mixed effects model was used with limb as a random factor, and group, trunk restraint, and shoulder abduction load as fixed factors for quantifying changes in reaching distance expressed percent limb length (% LL). Findings: Across limbs (paretic, non-paretic, control), when the trunk was un-restrained, reaching distance was reduced (p<.05). Further reduction in reaching distance was observed in the paretic compared to the non-paretic and control (p< .05) limbs. Reaching velocity was fastest for controls (3.26 {+/-} 1.52 m/s) compared to non-paretic (3.24 {+/-} 1.19 m/s) and paretic (1.59 {+/-} 1.32 m/s) limbs in stroke. Shoulder abduction loading had an effect on reaching distance in the paretic limb (p<.05) Table: .83 {+/-} .13 % LL, 25% MVT: .77 {+/-} .14 % LL, 50% MVT: .76 {+/-} .15 %LL). Greater shoulder excursion occurred during non-paretic limb reaching compared to the paretic limb with an increase of 14.80 mm (p<.05). Conclusion: Active trunk control impacted reaching function and further reduced reaching distance in chronic hemiparetic stroke participants. However, the primary driver of reduced reaching distance was the flexion synergy. While reaching speed increased the demand at the trunk, excursions were comparable during paretic and non-paretic limb reaching, suggesting that overall trunk function was intact during this paradigm.

bioengineering↗

bioRxiv2019

Volume and intramuscular fat content of upper extremity muscles in individuals with chronic hemiparetic stroke

Stroke survivors often experience upper extremity deficits that make activities of daily living (ADLs) like dressing, cooking and bathing difficult or impossible. Survivors experience paresis, the inability to efficiently and fully activate muscles, which combined with decreased use of the upper extremity, will lead to muscle atrophy and potentially an increase in intramuscular fat. Muscle atrophy has been linked to weakness post stroke and is an important contributor to upper extremity deficits. However, the extent of upper extremity atrophy post hemiparetic stroke is unknown and a better understanding of these changes is needed to inform the direction of intervention-based research. In this study, the volume of contractile tissue and intramuscular fat in the elbow and wrist flexors and extensors were quantified in the paretic and non-paretic upper limb using MRI and the Dixon technique for the first time. Total muscle volume (p[≤]0.0005) and contractile element volume (p[≤]0.0005) were significantly smaller in the paretic upper extremity, for all muscle groups studied. The average percent difference between limbs and across participants was 21.3% for muscle volume and 22.9% for contractile element volume. We also found that while the percent intramuscular fat was greater in the paretic limb compared to the non-paretic (p[≤]0.0005), however, the volume of intramuscular fat was not significantly different between upper limbs (p=0.231). The average volumes of intramuscular fat for the elbow flexors/extensors and wrist flexors/extensors were 28.1, 28.8 and 19.9, 8.8 cm3 in the paretic limb and 29.6, 27.7 and 19.7, 8.8 cm3 in the non-paretic limb. In short, these findings indicate a decrease in muscle volume and not an increase in intramuscular fat, which will contribute to the reduction in strength in the paretic upper limb.

bioengineering↗

bioRxiv2019

Reduction in voluntary activation of elbow and wrist muscles in individuals with chronic hemiparetic stroke

After a stroke, descending drive is impaired due to the loss of corticospinal and corticobulbar projections which causes a reduction in voluntary activation or an inability of the nervous system to activate muscles to their full capacity, which in turn contributes to weakness of the upper extremity. Voluntary activation has not been quantified at specific joints in the upper extremity, in part because directly assessing changes descending drive is difficult. In this study, voluntary activation of elbow and wrist flexors and extensors was assessed in participants with chronic hemiparetic stroke using twitch interpolation. Twitch interpolation uses electrical stimulation to estimate voluntary activation and relies on the principle that there is an inverse relationship between the amplitude of a twitch evoked by a stimulus and the voluntary force output during stimulation (Taylor, 2009). We measured voluntary activation using twitch interpolation as well as maximum voluntary torque (MVT) of the elbow and wrist flexors and extensors in the paretic and non-paretic limb of ten participants post stroke and the dominant and non-dominant limb of 2 control participants. Results show, MVT interlimb differences were significantly greater for stroke participants compared to control, across muscle groups (p[≤]0.005). For stroke participants, MVT interlimb differences were significantly greater at the wrist compared to the elbow (P=0.003). Voluntary activation was significantly less in the paretic limb compared to the non-paretic, dominant and non-dominant limbs, across participants and muscle groups (p<0.005 for all four muscle groups). For the stroke participants, the voluntary activation interlimb difference was significantly greater for the wrist muscles compared to the elbow muscles (p<0.005). There was a significant positive correlation (r = 0.39, P = .022) between each participants impairment level, as measured by a hand specific subscore of the Fugl-Meyer Assessment, and the wrist extensor voluntary activation in the paretic limb but the relationship was not significant for the other muscle groups.

bioengineering↗