Biology subjects

Yen, S.-C.

Publications and source records attributed to Yen, S.-C..

4 recordsLinked to original sources

bioRxiv2019

Neuromodulation of pelvic nerve during early phase of spinal cord injury in rats using implantable prototype devices - a preliminary study.

ObjectivesThe bladder becomes retentive during the early phase of spinal cord injury, and requires proper bladder management to prevent damage to the lower urinary tract and kidney. We investigated the effects of on-demand pelvic nerve stimulation on the areflexive bladder during the earliest phase of complete spinal cord injury in rats and the use of pelvic nerve signals as a proxy to estimate intravesical pressure for closed-loop applications.\n\nMaterials and MethodsIn order to stimulate the pelvic nerves in female Sprague-Dawley rats with complete spinal cord transection (T7 level), a flexible electrode was implanted unilaterally on pelvic nerve, and electrical stimulation was provided by a custom-built nerve stimulator. Stimulation-evoked voiding was monitored in the awake state while size, capacity and spontaneous contractions of the bladder were analysed under anaesthesia. Separately, recordings of the pelvic nerve signals, external urethral sphincter activity and intravesical pressure were performed in animals with intact and transected spinal cord under anaesthesia.\n\nResultsSuccessful pelvic nerve stimulation enabled more frequent voiding, reduced overdistension of bladder, and preserved non-voiding spontaneous bladder contractions. Typical bladder management protocol for SCI rats (manual expression every 8 - 12 hours) resulted in more severe bladder overdistention. Signal processing of the recorded extraneural pelvic nerve signals successfully reconstructed changes in intravesical pressure, demonstrating their use in estimating the fullness and contractions of the bladder.\n\nConclusionsThe preliminary results suggest that pelvic nerve stimulators can serve as an alternative method for frequent emptying of the areflexive bladder. Simultaneous recording of the same pelvic nerve will be useful for development of a closed-loop neuroprosthesis.

neuroscience↗

bioRxiv2019

Independent Activity Subspaces for Working Memory and Motor Preparation in the Lateral Prefrontal Cortex

The lateral prefrontal cortex is involved in the integration of multiple types of information, including working memory and motor preparation. However, it is not known how downstream regions can extract one type of information without interference from the others present in the network. Here we show that the lateral prefrontal cortex contains two independent low-dimensional subspaces: one that encodes working memory information, and another that encodes motor preparation information. These subspaces capture all the information about the target in the delay periods, and the information in both subspaces is reduced in error trials. A single population of neurons with mixed selectivity forms both subspaces, but the information is kept largely independent from each other. A bump attractor model with divisive normalization replicates the properties of the neural data. These results have implications for the neural mechanisms of cognitive flexibility and capacity limitations.

neuroscience↗

bioRxiv2019

Time-Invariant Working Memory Representations in the Presence of Code-Morphing in the Lateral Prefrontal Cortex

Endogenous processes allow the maintenance of working memories. These processes presumably involve prefrontal networks with strong recurrent connections. Distractors evoke a morphing of the population code, even when memories are stable. But it is unclear whether these dynamic population responses contain stable memory information. Here we show that dynamic prefrontal activity contains stable memory information, and the stability depends on parallel movement of trajectories associated with different memories in state space. We used an optimization algorithm to find a subspace with stable memory information. In correct trials the stability extended to periods that were not used to find the subspace, but in error trials the information and the stability were reduced. A bump attractor model was able to replicate these behaviors. The model provided predictions that could be confirmed with the neural data. We conclude that downstream regions could read memory information from a stable subspace.

neuroscience↗

bioRxiv2018

Visuomotor Control of Ankle Joint using Position vs. Force

Ankle joint plays a critical role in daily activities involving interactions with environment using force and position control. Neuromechanical dysfunctions (e.g. due to stroke or brain injury), therefore, have a major impact on individuals quality of life. The effective design of neurorehabilitation protocols for robotic rehabilitation platforms, relies on understanding the control characteristics of the ankle joint in interaction with external environment using force and position. This is particularly of interest since the findings in upper-limb may not be generalizable to the lower-limb. This study aimed to characterize the skilled performance of ankle joint in visuomotor position and force control. A 2-degree of freedom (DOF) robotic footplate was used to measure individuals force and position. Healthy individuals (n = 27) used ankle force or position for point-to-point and tracking control tasks in 1-DOF and 2-DOF virtual game environments. Subjects performance was quantified as a function of accuracy and completion time. While the performance measures in 1-DOF control tasks were comparable, the subjects performance in 2-DOF tasks was significantly better with position control. Subjective questionnaires on the perceived difficulty matched the objective experimental results; suggesting that the poor performance in force control was not due to experimental setup or fatigue but can be attributed to the different levels of challenge needed in neural control. It is inferred that in visuomotor coordination, the neuromuscular specialization of ankle provides better control over position rather than force. These findings can inform the design of neuro-rehabilitation platforms, selection of effective tasks, and therapeutic protocols.

neuroscience↗