@article {4569, title = {Bidirectional locomotion induces unilateral limb adaptations.}, journal = {bioRxiv}, year = {2024}, month = {2024 Aug 23}, abstract = {

Humans can acquire and maintain motor skills throughout their lives through motor learning. Motor learning and skill acquisition are essential for rehabilitation following neurological disease or injury. Adaptation, the initial stage of motor learning, involves short-term changes in motor performance in response to a new demand in the person{\textquoteright}s environment. Repeated adaptation can improve skill performance and result in long-term skill retention. Locomotor adaptation is extensively studied using split-belt treadmill paradigms. In this study we explored whether bidirectional walking (BDW) on a split-belt treadmill can induce short-term gait adaptations. Twelve healthy volunteers participated in our single session, starting with 2 minutes of normal walking (NW), followed by four 5-minute blocks of BDW with a 1-minute passive rest in between blocks, and ending with another 2-minute of NW. We recorded body kinematics and ground reaction forces throughout the experiment. Participants quickly adapted to BDW with both legs showing decreased step lengths. However, only the backward-walking leg exhibited aftereffects upon returning to NW, indicating short-term adaptation. Notable kinematic changes were observed, particularly in hip extension and pelvis tilt, though these varied among participants. Our findings suggest that BDW induces unilateral adaptations despite bilateral changes in gait, offering new insights into locomotor control and spinal CPG organization.

}, issn = {2692-8205}, doi = {10.1101/2024.08.22.609228}, author = {Hardesty, Russell L and Motjabavi, Helia and Gemoets, Darren E and Wolpaw, Jonathan R} } @article {4579, title = {Motor learning changes the axon initial segment of the spinal motoneuron.}, journal = {J Physiol}, volume = {602}, year = {2024}, month = {2024 May}, pages = {2107-2126}, abstract = {

We are studying the mechanisms of H-reflex operant conditioning, a simple form of learning. Modelling studies in the literature and our previous data suggested that changes in the axon initial segment (AIS) might contribute. To explore this, we used blinded quantitative histological and immunohistochemical methods to study in adult rats the impact of H-reflex conditioning on the AIS of the spinal motoneuron that produces the reflex. Successful, but not unsuccessful, H-reflex up-conditioning was associated with greater AIS length and distance from soma; greater length correlated with greater H-reflex increase. Modelling studies in the literature suggest that these increases may increase motoneuron excitability, supporting the hypothesis that they may contribute to H-reflex increase. Up-conditioning did not affect AIS ankyrin G (AnkG) immunoreactivity (IR), p-p38 protein kinase IR, or GABAergic terminals. Successful, but not unsuccessful, H-reflex down-conditioning was associated with more GABAergic terminals on the AIS, weaker AnkG-IR, and stronger p-p38-IR. More GABAergic terminals and weaker AnkG-IR correlated with greater H-reflex decrease. These changes might potentially contribute to the positive shift in motoneuron firing threshold underlying H-reflex decrease; they are consistent with modelling suggesting that sodium channel change may be responsible. H-reflex down-conditioning did not affect AIS dimensions. This evidence that AIS plasticity is associated with and might contribute to H-reflex conditioning adds to evidence that motor learning involves both spinal and brain plasticity, and both neuronal and synaptic plasticity. AIS properties of spinal motoneurons are likely to reflect the combined influence of all the motor skills that share these motoneurons. KEY POINTS: Neuronal action potentials normally begin in the axon initial segment (AIS). AIS plasticity affects neuronal excitability in development and disease. Whether it does so in learning is unknown. Operant conditioning of a spinal reflex, a simple learning model, changes the rat spinal motoneuron AIS. Successful, but not unsuccessful, H-reflex up-conditioning is associated with greater AIS length and distance from soma. Successful, but not unsuccessful, down-conditioning is associated with more AIS GABAergic terminals, less ankyrin G, and more p-p38 protein kinase. The associations between AIS plasticity and successful H-reflex conditioning are consistent with those between AIS plasticity and functional changes in development and disease, and with those predicted by modelling studies in the literature. Motor learning changes neurons and synapses in spinal cord and brain. Because spinal motoneurons are the final common pathway for behaviour, their AIS properties probably reflect the combined impact of all the behaviours that use these motoneurons.

}, keywords = {Animals, Ankyrins, Axon Initial Segment, Axons, Conditioning, Operant, H-Reflex, Learning, Male, Motor Neurons, Neuronal Plasticity, Rats, Rats, Sprague-Dawley, Spinal Cord}, issn = {1469-7793}, doi = {10.1113/JP283875}, author = {Wang, Yu and Chen, Yi and Chen, Lu and Herron, Bruce J and Chen, Xiang Yang and Wolpaw, Jonathan R} } @article {4460, title = {Effects of active and sham tDCS on the soleus H-reflex during standing.}, journal = {Exp Brain Res}, volume = {241}, year = {2023}, month = {06/2023}, pages = {1611-1622}, abstract = {

Weak transcranial direct current stimulation (tDCS) is known to affect corticospinal excitability and enhance motor skill acquisition, whereas its effects on spinal reflexes in actively contracting muscles are yet to be established. Thus, in this study, we examined the acute effects of Active and Sham tDCS on the soleus H-reflex during standing. In fourteen adults without known neurological conditions, the soleus H-reflex was repeatedly elicited at just above M-wave threshold throughout 30~min of Active (N = 7) or Sham (N = 7) 2-mA tDCS over the primary motor cortex in standing. The maximum H-reflex (H) and M-wave (M) were also measured before and immediately after 30~min of tDCS. The soleus H-reflex amplitudes became significantly larger (by 6\%) ≈1~min into Active or Sham tDCS and gradually returned toward the pre-tDCS values, on average, within 15~min. With Active tDCS, the amplitude reduction from the initial increase appeared to occur more swiftly than with Sham tDCS. An acute temporary increase in the soleus H-reflex amplitude within the first minute of Active and Sham tDCS found in this study indicates a previously unreported effect of tDCS on the H-reflex excitability. The present study suggests that neurophysiological characterization of Sham tDCS effects is just as important as investigating Active tDCS effects in understanding and defining acute effects of tDCS on the excitability of spinal reflex pathways.

}, keywords = {Adult, Evoked Potentials, Motor, H-Reflex, Humans, Muscle, Skeletal, Standing Position, Transcranial Direct Current Stimulation}, issn = {1432-1106}, doi = {10.1007/s00221-023-06624-7}, author = {McCane, Lynn M and Wolpaw, Jonathan R and Thompson, Aiko K} } @article {4450, title = {Towards clinical application of implantable brain-computer interfaces for people with late-stage ALS: medical and ethical considerations.}, journal = {J Neurol}, volume = {270}, year = {2023}, month = {03/2023}, pages = {1323-1336}, abstract = {

Individuals with amyotrophic lateral sclerosis (ALS) frequently develop speech and communication problems in the course of their disease. Currently available augmentative and alternative communication technologies do not present a solution for many people with advanced ALS, because these devices depend on residual and reliable motor activity. Brain-computer interfaces (BCIs) use neural signals for computer control and may allow people with late-stage ALS to communicate even when conventional technology falls short. Recent years have witnessed fast progression in the development and validation of implanted BCIs, which place neural signal recording electrodes in or on the cortex. Eventual widespread clinical application of implanted BCIs as an assistive communication technology for people with ALS will have significant consequences for their daily life, as well as for the clinical management of the disease,~among others because of the potential interaction between the BCI and other procedures people with ALS undergo, such as tracheostomy. This article aims to facilitate responsible real-world implementation of implanted BCIs. We review the state of the art of research on implanted BCIs for communication, as well as the medical and ethical implications of the clinical application of this technology. We conclude that the contribution of all BCI stakeholders, including clinicians of the various ALS-related disciplines, will be needed to develop procedures for, and shape the process of, the responsible clinical application of implanted BCIs.

}, keywords = {Amyotrophic Lateral Sclerosis, brain-computer interfaces, Electroencephalography, Humans, Self-Help Devices, Speech}, issn = {1432-1459}, doi = {10.1007/s00415-022-11464-6}, author = {Vansteensel, Mariska J and Klein, Eran and van Thiel, Ghislaine and Gaytant, Michael and Simmons, Zachary and Wolpaw, Jonathan R and Vaughan, Theresa M} } @article {4436, title = {The Evoked Potential Operant Conditioning System (EPOCS): A Research Tool and an Emerging Therapy for Chronic Neuromuscular Disorders.}, journal = {J Vis Exp}, year = {2022}, month = {2022 08 25}, abstract = {

The Evoked Potential Operant Conditioning System (EPOCS) is a software tool that implements protocols for operantly conditioning stimulus-triggered muscle responses in people with neuromuscular disorders, which in turn can improve sensorimotor function when applied appropriately. EPOCS monitors the state of specific target muscles-e.g., from surface electromyography (EMG) while standing, or from gait cycle measurements while walking on a treadmill-and automatically triggers calibrated stimulation when pre-defined conditions are met. It provides two forms of feedback that enable a person to learn to modulate the targeted pathway{\textquoteright}s excitability. First, it continuously monitors ongoing EMG activity in the target muscle, guiding the person to produce a consistent level of activity suitable for conditioning. Second, it provides immediate feedback of the response size following each stimulation and indicates whether it has reached the target value. To illustrate its use, this article describes a protocol through which a person can learn to decrease the size of the Hoffmann reflex-the electrically-elicited analog of the spinal stretch reflex-in the soleus muscle. Down-conditioning this pathway{\textquoteright}s excitability can improve walking in people with spastic gait due to incomplete spinal cord injury. The article demonstrates how to set up the equipment; how to place stimulating and recording electrodes; and how to use the free software to optimize electrode placement, measure the recruitment curve of direct motor and reflex responses, measure the response without operant conditioning, condition the reflex, and analyze the resulting data. It illustrates how the reflex changes over multiple sessions and how walking improves. It also discusses how the system can be applied to other kinds of evoked responses and to other kinds of stimulation, e.g., motor evoked potentials to transcranial magnetic stimulation; how it can address various clinical problems; and how it can support research studies of sensorimotor function in health and disease.

}, keywords = {Chronic Disease, Conditioning, Operant, Electromyography, Evoked Potentials, H-Reflex, Humans, Neuromuscular Diseases, Spinal Cord Injuries}, issn = {1940-087X}, doi = {10.3791/63736}, author = {Hill, N Jeremy and Gupta, Disha and Eftekhar, Amir and Brangaccio, Jodi A and Norton, James J S and McLeod, Michelle and Fake, Tim and Wolpaw, Jonathan R and Thompson, Aiko K} } @article {4453, title = {Heksor: the central nervous system substrate of an adaptive behaviour.}, journal = {J Physiol}, volume = {600}, year = {2022}, month = {08/2022}, pages = {3423-3452}, abstract = {

Over the past half-century, the largely hardwired central nervous system (CNS) of 1970~has become the ubiquitously plastic CNS of today, in which change is the rule not the exception. This transformation complicates a central question in neuroscience: how are adaptive behaviours - behaviours that serve the needs of the individual - acquired and maintained through life? It poses a more basic question: how do many adaptive behaviours share the ubiquitously plastic CNS? This question compels neuroscience to adopt a new paradigm. The core of this paradigm is a CNS entity with unique properties, here given the name heksor from the Greek hexis. A heksor is a distributed network of neurons and synapses that changes itself as needed to maintain the key features of an adaptive behaviour, the features that make the behaviour satisfactory. Through their concurrent changes, the numerous heksors that share the CNS negotiate the properties of the neurons and synapses that they all use. Heksors keep the CNS in a state of negotiated equilibrium that enables each heksor to maintain the key features of its behaviour. The new paradigm based on heksors and the negotiated equilibrium they create is supported by animal and human studies of interactions among new and old adaptive behaviours, explains otherwise inexplicable results, and underlies promising new approaches to restoring behaviours impaired by injury or disease. Furthermore, the paradigm offers new and potentially important answers to extant questions, such as the generation and function of spontaneous neuronal activity, the aetiology of muscle synergies, and the control of homeostatic plasticity.

}, keywords = {Adaptation, Psychological, Animals, central nervous system, Humans, Neuronal Plasticity, Plastics, Synapses}, issn = {1469-7793}, doi = {10.1113/JP283291}, author = {Wolpaw, Jonathan R and Kamesar, Adam} } @article {4495, title = {Brain-computer interface-based assessment of color vision.}, journal = {J Neural Eng}, volume = {18}, year = {2021}, month = {2021 Nov 26}, abstract = {

Present methods for assessing color vision require the person{\textquoteright}s active participation. Here we describe a brain-computer interface-based method for assessing color vision that does not require the person{\textquoteright}s participation.This method uses steady-state visual evoked potentials to identify metamers-two light sources that have different spectral distributions but appear to the person to be the same color.We demonstrate that: minimization of the visual evoked potential elicited by two flickering light sources identifies the metamer; this approach can distinguish people with color-vision deficits from those with normal color vision; and this metamer-identification process can be automated.This new method has numerous potential clinical, scientific, and industrial applications.

}, keywords = {brain-computer interfaces, Color Vision, Electroencephalography, Evoked Potentials, Visual, Humans, Light, Photic Stimulation, Research Design}, issn = {1741-2552}, doi = {10.1088/1741-2552/ac3264}, author = {Norton, James J S and DiRisio, Grace F and Carp, Jonathan S and Norton, Amanda E and Kochan, Nicholas S and Wolpaw, Jonathan R} } @article {4366, title = {Breathable, large-area epidermal electronic systems for recording electromyographic activity during operant conditioning of H-reflex.}, journal = {Biosens Bioelectron}, volume = {165}, year = {2020}, month = {10/2020}, pages = {112404}, abstract = {

Operant conditioning of Hoffmann{\textquoteright}s reflex (H-reflex) is a non-invasive and targeted therapeutic intervention for patients with movement disorders following spinal cord injury. The reflex-conditioning protocol uses electromyography (EMG) to measure reflexes from specific muscles elicited using transcutaneous electrical stimulation. Despite recent advances in wearable electronics, existing EMG systems that measure muscle activity for operant conditioning of spinal reflexes still use rigid metal electrodes with conductive gels and aggressive adhesives, while requiring precise positioning to ensure reliability of data across experimental sessions. Here, we present the first large-area epidermal electronic system (L-EES) and demonstrate its use in every step of the reflex-conditioning protocol. The L-EES is a stretchable and breathable composite of nanomembrane electrodes (16 electrodes in a four by four array), elastomer, and fabric. The nanomembrane electrode array enables EMG recording from a large surface area on the skin and the breathable elastomer with fabric is biocompatible and comfortable for patients. We show that L-EES can record direct muscle responses (M-waves) and H-reflexes, both of which are comparable to those recorded using conventional EMG recording systems. In addition, L-EES may improve the reflex-conditioning protocol; it has potential to automatically optimize EMG electrode positioning, which may reduce setup time and error across experimental sessions.

}, keywords = {Biosensing Techniques, Conditioning, Operant, Electronics, H-Reflex, Humans, Reproducibility of Results}, issn = {1873-4235}, doi = {10.1016/j.bios.2020.112404}, author = {Kwon, Young-Tae and Norton, James J S and Cutrone, Andrew and Lim, Hyo-Ryoung and Kwon, Shinjae and Choi, Jeongmoon J and Kim, Hee Seok and Jang, Young C and Wolpaw, Jonathan R and Yeo, Woon-Hong} }