Biology subjects

Gassass, S.

Publications and source records attributed to Gassass, S..

3 recordsLinked to original sources

bioRxiv2026

Functional connectivity during drawing after upper extremity peripheral nerve surgery: enhanced connectivity between motor and visuomotor-parietal regions

ImportanceRecovery after upper extremity peripheral nerve injury (PNI) surgery depends on changes in cortical neural patterns that support sensorimotor control. Task-based functional connectivity (FC) can characterize these changes, yet few studies have explored FC during ecologically fine motor valid tasks after PNI. ObjectiveTo investigate task-based FC with the left primary motor cortex (M1) during right hand drawing in individuals following right hand PNI surgery. ParticipantsForty-four right-handed adults, including 12 patients post PNI surgery (n = 8 with nerve repair, n = 4 with nerve transfer) and 32 healthy controls. MethodsAll participants underwent fMRI while performing a RH visuomotor precision drawing task. Seed-based connectivity analysis was performed to characterize the pattern of FC between left M1 and all voxels in the brain. We hypothesized that left M1 FC would differ between patients and controls, between Repair and Transfer groups, and covary with time since surgery. ResultsPatients (vs. controls) showed greater FC between left M1 and right visual and premotor cortices. Nerve transfer (vs. repair) showed greater FC between left M1 and right inferior parietal areas. Time since surgery was not linearly related to FC, though exploratory analyses suggested a negative association between log-time and FC between left M1 and right inferior parietal lobule. ConclusionAfter PNI surgery, visuomotor precision drawing involved distinct and behaviorally relevant neural patterns, which varied by task demand and potentially by surgical group despite clinical heterogeneity. Inferior parietal cortex may be especially engaged in early months after surgery (i.e. log-time). To improve recovery of upper limb function after PNI, clinical recommendations include incorporating early function-specific dexterous training, tailoring rehabilitation across surgical and recovery stages, and using multidimensional assessments of hand function.

neuroscience↗

bioRxiv2025

Neural mechanisms of handedness for precision drawing: hand-dependent engagement of cortical networks for bimanual control and tool use

Neural mechanisms underlying handedness remain poorly understood. We used functional magnetic resonance imaging (fMRI) to study performance of a visually guided drawing task with each hand. We hypothesized that the left superior parietal lobule supports drawing with either hand, and individuals with chronic peripheral nerve injury (PNI) to the dominant hand use the same mechanism as healthy adults. Thirty-three right-handed adults (23 healthy, 10 patients) underwent fMRI while performing a precision drawing task, alternating between the right hand (RH) and left hand (LH). BOLD magnitude and functional connectivity (FC) modulation via generalized psychophysiological interaction were analyzed in 12 a priori regions of interest, followed by additional exploratory areas identified via whole brain magnitude analysis. During LH drawing (compared to RH drawing), contralateral primary motor cortex showed lower BOLD magnitude but greater FC with two networks: First, a left motor-premotor network with increased FC and equal-or-greater magnitude during LH drawing. Second, a right parietal network characterized by increased FC during LH drawing but increased magnitude during RH drawing. Exploratory whole-brain analyses supported and extended these motor and parietal networks, and additionally suggested that RH drawing may involve greater magnitude and FC within a bilateral parieto-premotor network centered on right paracingulate cortex. Patient group (PNI vs. control) did not interact with these effects. These results describe the first proposed mechanisms for LH precision drawing, both of which depend on differential engagement of bimanual control networks: a left hemisphere motor-premotor network for precision motor control, which engages intrahemispherically (directly) during RH drawing and interhemispherically (indirectly) during LH drawing; and a right hemisphere parietal network with greater distributed coordination during LH drawing. These mechanisms did not differ between PNI patients and healthy adults, highlighting these mechanisms potential as neuromodulatory targets to enhance LH performance after RH impairment.

neuroscience↗

bioRxiv2023

Healthy adults favor stable left/right hand choices over performance at an unconstrained reach-to-grasp task

Reach-to-grasp actions are fundamental to the daily activities of human life, but few methods exist to assess individuals reaching and grasping actions in unconstrained environments. The Block Building Task (BBT) provides an opportunity to directly observe and quantify these actions, including left/right hand choices. Here we sought to investigate the motor and non-motor causes of left/right hand choices, and optimize the design of the BBT, by manipulating motor and non-motor difficulty in the BBTs unconstrained reach-to-grasp task We hypothesized that greater motor and non-motor (e.g. cognitive/perceptual) difficulty would drive increased usage of the dominant hand. To test this hypothesis, we modulated block size (large vs. small) to influence motor difficulty, and model complexity (10 vs. 5 blocks per model) to influence non-motor difficulty, in healthy adults (n=57). We hypothesized that healthy adults with high non-dominant hand performance in a precision drawing task should be more likely to use their non-dominant hand in the BBT. Our data revealed that increased motor and non-motor difficulty led to lower task performance (slower speed), but participants only increased use of their dominant hand only under the most difficult combination of conditions: in other words, participants allowed their performance to degrade before changing hand choices, even though participants were instructed only to optimize performance. These results demonstrate that hand choices during reach-to grasp actions are more stable than motor performance in healthy right-handed adults, but tasks with multifaceted difficulties can drive individuals to rely more on their dominant hand. Statements and DeclarationsDr. Philip and Washington University in St. Louis have a licensing agreement with PlatformSTL to commercialize the iPad app used in this study.

neuroscience↗