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1. A blended neurostimulation protocol to delineate cortico-muscular and spino-muscular dynamics following neuroplastic adaptation

   https://doi.org/10.3389/fneur.2023.1114860  

   Stefanovic, Filip ; Martinez, Julian A. ; Saleem, Ghazala T. ; Sisto, Sue Ann ; Miller, Michael T. ; Achampong, Yaa A. ; Titus, Albert H. ( June 2023 , Frontiers in Neurology)

   In this paper we propose a novel neurostimulation protocol that provides an intervention-based assessment to distinguish the contributions of different motor control networks in the cortico-spinal system. Specifically, we use a combination of non-invasive brain stimulation and neuromuscular stimulation to probe neuromuscular system behavior with targeted impulse-response system identification. In this protocol, we use an in-house developed human-machine interface (HMI) for an isotonic wrist movement task, where the user controls a cursor on-screen. During the task, we generate unique motor evoked potentials based on triggered cortical or spinal level perturbations. Externally applied brain-level perturbations are triggered through TMS to cause wrist flexion/extension during the volitional task. The resultant contraction output and related reflex responses are measured by the HMI. These movements also include neuromodulation in the excitability of the brain-muscle pathway via transcranial direct current stimulation. Colloquially, spinal-level perturbations are triggered through skin-surface neuromuscular stimulation of the wrist muscles. The resultant brain-muscle and spinal-muscle pathways perturbed by the TMS and NMES, respectively, demonstrate temporal and spatial differences as manifested through the human-machine interface. This then provides a template to measure the specific neural outcomes of the movement tasks, and in decoding differences in the contribution of cortical- (long-latency) and spinal-level (short-latency) motor control. This protocol is part of the development of a diagnostic tool that can be used to better understand how interaction between cortical and spinal motor centers changes with learning, or injury such as that experienced following stroke.

    

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2. Effect of spinal cord injury on neural encoding of spontaneous postural perturbations in the hindlimb sensorimotor cortex

   Jaimie B Dougherty ( January 2021 , Journal of neurophysiology)

   Capers, Miriam (Ed.)

   Supraspinal signals play a significant role in compensatory responses to postural perturbations after spinal cord injury (SCI). SCI disrupts descending motor control signals as well as ascending somatosensory information to and from below the lesion. In intact animals, While cortical signals are not necessary for basic postural tasks, but neurons in the motor cortex have been shown to respond to periodic postural perturbations in intact animals. However, the role of the cortex in postural control after spinal cord injury in response to unexpected postural perturbations has not been studied. To better understand how spinal lesions impact cortical encoding of information about unexpected postural perturbations, the activity of single neurons in the rat hindlimb sensorimotor cortex (HLSMC) were recorded during unexpected tilts before and after a complete midthoracic spinal transection. In a subset of animals, limb ground reaction forces were collected as well. Results show that responses in the HLSMC were modulated with changes in tilt severity (i.e. tilt velocity). As initial velocity of the tilt increased, more information was conveyed by the HLSMC neurons about the perturbation due to increases in both the number of recruited neurons and the magnitude of their response. After SCI hindlimb ground reaction forces were both attenuated and delayed, and the neural responses were delayed and less likely to respond to slower tilts. This resulted in a moderate decrease inan attenuation of the information conveyed by cortical neurons about the tilts, requiring more cells to convey the same amount of information as before the transection. Given that reorganization of the hindlimb sensorimotor cortex in response to therapy after complete mid-thoracic SCI is necessary for behavioral recovery, this sustained encoding of information after SCI could be a substrate for the reorganization that uses sensory information from above the lesion to control trunk muscles that permit weight-supported stepping and postural control. 

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3. 66361 TL1 Team Approach to Predicting Response to Spinal Cord Stimulation for Chronic Low Back Pain

   https://doi.org/10.1017/cts.2021.685  

   See, Kyle ; Ho, Rachel ; Coombes, Stephen ; Fang, Ruogu ( March 2021 , Journal of Clinical and Translational Science)

   ABSTRACT IMPACT: Understanding how spinal cord stimulation works and who it works best for will improve clinical trial efficacy and prevent unnecessary surgeries. OBJECTIVES/GOALS: Spinal cord stimulation (SCS) is an intervention for chronic low back pain where standard interventions fail to provide relief. However, estimates suggest only 58% of patients achieve at least 50% reduction in their pain. There is no non-invasive method for predicting relief provided by SCS. We hypothesize neural activity in the brain can fill this gap. METHODS/STUDY POPULATION: We tested SCS patients at 3 times points: baseline (pre-surgery), at day 7 during the trial period (post-trial), and 6 months after a permanent system had been implanted. At each time point participants completed 10 minutes of eyes closed, resting electroencephalography (EEG) and self-reported their pain. EEG was collected with the ActiveTwo system and a 128-electrode cap. Patients were grouped based on the percentage change of their pain from baseline to the final visit using a median split (super responders > average responders). Spectral density powerbands were extracted from resting EEG to use as input features for machine learning analyses. We used support vector machines to predict response to SCS. RESULTS/ANTICIPATED RESULTS: Baseline and post-trial EEG data predicted SCS response at 6-months with 95.56% and 100% accuracy, respectively. The gamma band had the highest performance in differentiating responders. Post-trial EEG data best differentiated the groups with feature weighted dipoles being more highly localized in sensorimotor cortex. DISCUSSION/SIGNIFICANCE OF FINDINGS: Understanding how SCS works and who it works best for is the long-term objective of our collaborative research program. These data provide an important first step towards this goal. 

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4. Hybrid FES-exoskeleton control: Using MPC to distribute actuation for elbow and wrist movements

   https://doi.org/10.3389/fnbot.2023.1127783  

   Dunkelberger, Nathan ; Berning, Jeffrey ; Schearer, Eric M. ; O'Malley, Marcia K. ( April 2023 , Frontiers in Neurorobotics)

   Individuals who have suffered a cervical spinal cord injury prioritize the recovery of upper limb function for completing activities of daily living. Hybrid FES-exoskeleton systems have the potential to assist this population by providing a portable, powered, and wearable device; however, realization of this combination of technologies has been challenging. In particular, it has been difficult to show generalizability across motions, and to define optimal distribution of actuation, given the complex nature of the combined dynamic system.

   In this paper, we present a hybrid controller using a model predictive control (MPC) formulation that combines the actuation of both an exoskeleton and an FES system. The MPC cost function is designed to distribute actuation on a single degree of freedom to favor FES control effort, reducing exoskeleton power consumption, while ensuring smooth movements along different trajectories. Our controller was tested with nine able-bodied participants using FES surface stimulation paired with an upper limb powered exoskeleton. The hybrid controller was compared to an exoskeleton alone controller, and we measured trajectory error and torque while moving the participant through two elbow flexion/extension trajectories, and separately through two wrist flexion/extension trajectories.

   The MPC-based hybrid controller showed a reduction in sum of squared torques by an average of 48.7 and 57.9% on the elbow flexion/extension and wrist flexion/extension joints respectively, with only small differences in tracking accuracy compared to the exoskeleton alone.

   To realize practical implementation of hybrid FES-exoskeleton systems, the control strategy requires translation to multi-DOF movements, achieving more consistent improvement across participants, and balancing control to more fully leverage the muscles' capabilities.

    

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5. Modulation of cortical beta oscillations influences motor vigor: A rhythmic TMS‐EEG study

   https://doi.org/10.1002/hbm.26149  

   Uehara, Kazumasa ; Fine, Justin M. ; Santello, Marco ( February 2023 , Human Brain Mapping)

   Abstract Previous electro‐ or magnetoencephalography (Electro/Magneto EncephaloGraphic; E/MEG) studies using a correlative approach have shown that β (13–30 Hz) oscillations emerging in the primary motor cortex (M1) are implicated in regulating motor response vigor and associated with an anti‐kinetic role, that is, slowness of movement. However, the functional role of M1 β oscillations in regulation of motor responses remains unclear. To address this gap, we combined EEG with rhythmic TMS (rhTMS) delivered to M1 at the β (20 Hz) frequency shortly before subjects performed an isometric ramp‐and‐hold finger force production task at three force levels. rhTMS is a novel approach that can modulate rhythmic patterns of neural activity. β‐rhTMS over M1 induced a modulation of neural oscillations to β frequency in the sensorimotor area and reduced peak force rate during the ramp‐up period relative to sham and catch trials. Interestingly, this rhTMS effect occurred only in the large force production condition. To distinguish whether the effects of rhTMS on EEG and behavior stemmed from phase‐resetting by each magnetic pulse or neural entrainment by the periodicity of rhTMS, we performed a control experiment using arrhythmic TMS (arTMS). arTMS did not induce changes in EEG oscillations nor peak force rate during the rump‐up period. Our results provide novel evidence that β neural oscillations emerging the sensorimotor area influence the regulation of motor response vigor. Furthermore, our findings further demonstrate that rhTMS is a promising tool for tuning neural oscillations to the target frequency. 

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