Biology subjects

Arac, A.

Publications and source records attributed to Arac, A..

4 recordsLinked to original sources

bioRxiv2025

Arm dominance emerges through asymmetric practice of complex trajectory shapes inherent to tool-use

Limb dominance is a human behavioral characteristic with many cultural, practical, scientific and clinical implications. Yet why the dominant limb performs better across a range of motor skill-requiring tasks remains unanswered. Is it because of an intrinsic hemispheric advantage or instead is it the result of life-long practice with the dominant side? We tested these alternatives using two tasks. The first was 3D reaching with either an inertial challenge or the need to use a stick-like tool. The second required participants to write with their dominant and non-dominant elbows. We applied a novel geometric analysis to quantify movement-trajectory shape. We show that (1) tool-use unmasks markedly inferior control in the non-dominant arm, and this is because tools impose the need to generate unfamiliarly shaped movement trajectories; and (2) there is no general dominant limb motor control advantage, only task-specific experience or practice. These results reframe dominance as predominantly about learned control of tool kinematics rather than baseline asymmetry in control of limb dynamics.

neuroscience↗

bioRxiv2023

Rab7a activation promotes degradation of select tight junction proteins at the blood-brain barrier after ischemic stroke

Adherens (AJ) and tight junction (TJ) integrity is critical for blood-brain barrier (BBB) function in the healthy brain. Junction disassembly due to degradation of AJ and TJ proteins leads to acute BBB dysfunction after ischemic stroke, but the mechanisms are not fully understood. Here, we show that endothelial cell deletion of Rab7a, a small GTPase crucial for protein degradation through the endolysosomal system, reduces acute BBB dysfunction and improves neuronal health in mice after ischemic stroke by preventing degradation of select junctional proteins and preserving TJ structural morphology. Two pro-inflammatory cytokines, TNF and IL1{beta}, that trigger barrier disruption in brain endothelial cells (BECs) in vitro and are upregulated in stroke, contribute to Rab7a activation. Silencing Rab7a in vitro partially rescues cytokine-driven barrier disruption in BECs by reducing internalization of some junctional proteins and the formation of F-actin bundles at cell junctions. Rab7a is, therefore, critical for degradation of select junctional proteins during the acute BBB damage after ischemic stroke.

cell biology↗

bioRxiv2023

Validation of marker-less pose estimation for 3D kinematics during upper limb reaching

Kinematic analysis of movement following brain damage is key for diagnosing motor impairments and for recovery assessment. Advances in computer vision offer novel marker-less tracking tools that could be implemented in the clinic due to their simple operation and affordability. An important question that arises is whether marker-less technologies are sufficiently accurate compared to well established marker-based technologies. This study aims to perform validation of kinematic assessment using two high-speed cameras and a 3D pose estimation model. Four participants performed reaching movements with the upper limb between fixed targets, in different velocities. Movement kinematics were simultaneously measured using the DeepBehavior model and marker-based optical motion capture (QTM), as a gold standard. The differences in corresponding joint angles, estimated from the two different methods throughout the analysis, are presented as a mean absolute error (MAE) of the elbow angle. Quantitatively, the MAE of all movements was relatively small across velocity and joints (~2{degrees}). In a condition where the movements were made towards the DeepBehavior cameras, and the view of the elbow was occluded in one of the cameras, the errors were higher. In conclusion, the results demonstrated that marker-less motion capture is a valid alternative to marker-based motion capture. Inaccuracies of the DeepBehavior system could be explained by occlusions of key-points and are not associated with failure of the pose estimation algorithm.

bioengineering↗

bioRxiv2022

Intrusion of pathological synergies does not explain impaired 3D arm movements in subacute stroke

It has long been of interest to characterize the components that generate the motor control abnormalities in the arm after stroke. One approach has been to decompose the hemiparesis phenotype into negative signs, such as weakness, and positive signs, such as intrusion of synergies. Here, we sought to identify the contributions of weakness and the flexor synergy to motor function and impairment, as defined by kinematic and clinical scales, respectively, in sub-acute stroke using two 3D arm tasks that differed in their requirement for elbow extension. Thirty-three sub-acute post-stroke participants and sixteen healthy controls performed a cup-to-mouth task, requiring shoulder and elbow flexion (within flexor synergy), and a reaching task, requiring shoulder flexion and elbow extension (out of flexor synergy). Using markerless 3D pose-estimation, we analyzed upper limb kinematics to assess overall task performance and intrusion of pathological synergies. Weakness was measured using a grip dynamometer. Performance in both tasks was impaired to a similar degree in the stroke participants compared to controls. Subsequent analysis of coordination patterns between the elbow and the shoulder joints revealed intrusion of synergies in the reaching task based on the time spent within a flexion-flexion pattern (flexor synergy proportion) and the correlation between shoulder and elbow angles when the shoulder was flexing (flexion synergy strength). Regression analysis indicated that the significant predictors of poor task performance were weakness and flexor synergy intrusion. Notably, the Fugl-Meyer Assessment was abnormal even when just weakness caused the impairment, which means that caution is required when using this scale to quantify synergies. We conclude that both weakness and synergy intrusion contribute to impaired coordination of the elbow and shoulder joints in the sub-acute post-stroke period. This study shows that careful kinematic analysis of naturalistic movements is required to better characterize the components of upper limb impairment after stroke.

neuroscience↗