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Neural stimulation therapies continue to evolve as new technologies are introduced into clinical practice. It has been over a decade since the initial descriptions of fully implantable, bidirectional neural systems, which allowed for concurrent sensing and stimulation, have been published. A major confounding issue in these types of neural recordings is the contamination of the signal of interest with electrical stimulus artifact, which can obscure short latency evoked activity and corrupt spectral analysis of longer duration signals. Approach. Here we describe the design and early preclinical evaluation of a neurostimulator with improved capabilities for sensing, with particular emphasis on managing stimulus artifact. The system was tested in three ovine deep brain stimulation (DBS) subjects, one with a DBS lead targeting the hippocampus, and two with DBS leads targeting the subthalamic nucleus (STN). All leads were externalized with percutaneous lead extensions. Main results. Results demonstrate that it was possible to record evoked potentials with a latency of 1–2 ms following stimulation in all subjects with the new system. Recordings from the hippocampal target showed clear short-latency responses exhibiting behavior consistent with evoked compound action potentials (ECAPs). In contrast, recordings from the STN target demonstrated highly resonant activity, dependent upon stimulus frequency, which could persist for 20–30 ms following individual stimuli. Both directional stimulation and directional recordings were evaluated to determine their influence on this evoked resonant neural activity (ERNA). The system was also characterized for sensing in one spinal cord stimulation (SCS) ovine subject and one sacral nerve modulation ovine subject. Significance. The bidirectional stimulation and evoked-response sensing system presented here enables sensing evoked responses elicited from stimulation, empowering continued research to expand the understanding and optimization of DBS therapy. Additionally, the example recordings from other therapy spaces demonstrate the capability of the system across neural stimulation therapies.

IntroductionSpinal cord injury (SCI) leads to significant changes in morbidity, mortality and quality of life (QOL). Currently, there are no effective therapies to restore function after chronic SCI. Preliminary studies have indicated that epidural spinal cord stimulation (eSCS) is a promising therapy to improve motor control and autonomic function for patients with chronic SCI. The aim of this study is to assess the effects of tonic eSCS after chronic SCI on quantitative outcomes of volitional movement and cardiovascular function. Our secondary objective is to optimise spinal cord stimulation parameters for volitional movement.Methods and analysisThe Epidural Stimulation After Neurologic Damage (ESTAND) trial is a phase II single-site self-controlled trial of epidural stimulation with the goal of restoring volitional movement and autonomic function after motor complete SCI. Participants undergo epidural stimulator implantation and are followed up over 15 months while completing at-home, mobile application-based movement testing. The primary outcome measure integrates quantity of volitional movement and similarity to normal controls using the volitional response index (VRI) and the modified Brain Motor Control Assessment. The mobile application is a custom-designed platform to support participant response and a kinematic task to optimise the settings for each participant. The application optimises stimulation settings by evaluating the parameter space using movement data collected from the tablet application and accelerometers. A subgroup of participants with cardiovascular dysautonomia are included for optimisation of blood pressure stabilisation. Indirect effects of stimulation on cardiovascular function, pain, sexual function, bowel/bladder, QOL and psychiatric measures are analysed to assess generalisability of this targeted intervention.Ethics and disseminationThis study has been approved after full review by the Minneapolis Medical Research Foundation Institutional Review Board and by the Minneapolis VA Health Care System. This project has received Food and Drug Administration investigational device exemption approval. Trial results will be disseminated through peer-reviewed publications, conference presentations and seminars.Trial registration numberNCT03026816.