Efficient Decoding With Steady-State Kalman Filter in Neural Interface Systems

The Kalman filter is commonly used in neural interface systems to decode neural activity and estimate the desired movement kinematics.We analyze a low-complexity Kalman filter implementation in which the filter gain is approximated by its steady-state form, computed offline before real-time decoding commences. We evaluate its performance using human motor cortical spike train data obtained from an intracortical recording array as part of an ongoing pilot clinical trial. We demonstrate that the standard Kalman filter gain converges to within 95% of the steady-state filter gain in 1.5[plus-over-minus sign]0.5 s (mean[plus-over-minus sign]s.d.) . The difference in the intended movement velocity decoded by the two filters vanishes within 5 s, with a correlation coefficient of 0.99 between the two decoded velocities over the session length. We also find that the steady-state Kalman filter reduces the computational load (algorithm execution time) for decoding the firing rates of 25[plus-over-minus sign]3 single units by a factor of 7.0[plus-over-minus sign]0.9. We expect that the gain in computational efficiency will be much higher in systems with larger neural ensembles. The steady-state filter can thus provide substantial runtime efficiency at little cost in terms of estimation accuracy. This far more efficient neural decoding approach will facilitate the practical implementation of future large-dimensional, multisignal neural interface systems.National Institutes of Health (U.S.) (Grant R01 DC009899)National Institutes of Health (U.S.) (Grant RC1 HD063931)National Institutes of Health (U.S.) (Grant N01 HD053403)National Institutes of Health (U.S.) (Grant 5K01 NS057389)National Institutes of Health (U.S.) (Grant DP1-OD003646)National Institutes of Health (U.S.) (Grant R01-EB006385)United States. Dept. of Veterans Affairs (Office of Research and Development, Rehabilitation R&D Service)Massachusetts General Hospital (Deane Institute for Integrated Research on Atrial Fibrillation and Stroke)Doris Duke Charitable FoundationSpaulding Rehabilitation Hospita

Watch, Imagine, Attempt: Motor Cortex Single-Unit Activity Reveals Context-Dependent Movement Encoding in Humans With Tetraplegia

Planning and performing volitional movement engages widespread networks in the human brain, with motor cortex considered critical to the performance of skilled limb actions. Motor cortex is also engaged when actions are observed or imagined, but the manner in which ensembles of neurons represent these volitional states (VoSs) is unknown. Here we provide direct demonstration that observing, imagining or attempting action activates shared neural ensembles in human motor cortex. Two individuals with tetraplegia (due to brainstem stroke or amyotrophic lateral sclerosis, ALS) were verbally instructed to watch, imagine, or attempt reaching actions displayed on a computer screen. Neural activity in the precentral gyrus incorporated information about both cognitive state and movement kinematics; the three conditions presented overlapping but unique, statistically distinct activity patterns. These findings demonstrate that individual neurons in human motor cortex reflect information related to sensory inputs and VoS in addition to movement features, and are a key part of a broader network linking perception and cognition to action

Principles of Augmentative and Alternative Communication System Design in the ICU Setting

Introduction: The ICU as a technology design setting requires specific and thoughtful awareness of patient-, caregiver-, and environment-related constraints. Designing an ICU-specific communication system involves an even deeper understanding of patient needs and desires, building on existing work exploring available technologies for use in this setting1,2. We report our initial experience from a pilot study with a novel communication device engineered specifically to allow mechanically ventilated ICU patients to communicate with caregivers3. Methods: We used a validated survey for nurses about communication purposes to explore relevant beliefs, attitudes, and desires of nurses4. Existing technologies available for communication assistance in the ICU – e.g., letter boards, writing on paper, and mouthing words – were analyzed. Suggestions about the content for an eventual communication system were collected. ICU-specific design requirements were noted, including adherence to infection control standards, accessibility to restrained patients, and availability to patients with motor weakness, contractures, edema, tremor, and/or neuropathy. In addition, the system must include a minimal learning curve, Results: Initial testing in the ICU has revealed additional considerations for technology design. For instance, many patients have visual impairments, so displays should be large and high-contrast. Furthermore, patients benefit from a very short teaching/demo process due to their short attention span. Additionally, leveraging interfaces with significant similarities to everyday systems appears to reduce confusion. Nurses also mentioned that the system should be accessible to at least some non-English-speaking patients. Finally, physical deficits that ICU patients experience require that manually operated devices be as flexible as possible in terms of type of manipulation required. Conclusions: ICU patients are in significant need of communication systems that meet their unique needs. Building such a system requires awareness of many different constraints, including both general heterogeneity of patient needs and capabilities and the constraints of the ICU setting itself

Testing a Novel Manual Communication System for Mechanically Ventilated ICU Patients

Introduction: Available communication methods for intubated patients in the ICU are insufficient to meet patient needs. Both ICU patients and their care providers report broadly unsuccessful communication attempts, resulting in less effective medical care and undue stress1,2. Use of existing methods - including letter boards, writing, and mouthing words - for mechanically ventilated (MV) patients has led to a consensus that new methods are required3. We report on the testing of a new system designed to address the communication needs of MV patients that is currently being tested in a low- to medium- acuity surgical ICU4. Methods: We have developed several generations of prototypes designed to address patient communication needs. Design of this device has focused on ICU-specific communication needs, including ICU-specific content, infection control, simple design, and capitalizing on motor movements that can be easily performed by most ICU patients. Initial testing, starting with non-MV patients able to give more detailed feedback, has begun in a low- to medium- acuity surgical ICU. Recently developed prototypes combine custom-built tablet software, focusing on the needs that nurses believe patients wish to express in the ICU setting, with a newly designed manually operated access device. The system produces visual and auditory output to allow patients to answer basic questions and effectively convey information. Results: Initial patient impressions are encouraging, particularly among patients who have recently experienced mechanical ventilation. Many patients are unfamiliar with tablet software or struggle with manual dexterity required to access the tablet screen directly, further indicating the need for an external access method as part of the system. The content suggested by nurses via a previously conducted survey has been confirmed by patients as relevant to their experience. Conclusions: A novel manually operated communication system has elicited both positive reviews and helpful feedback from patients

A high-performance speech neuroprosthesis

Speech brain-computer interfaces (BCIs) have the potential to restore rapid communication to people with paralysis by decoding neural activity evoked by attempted speech into tex

Neural population dynamics in human motor cortex during movements in people with ALS

The prevailing view of motor cortex holds that motor cortical neural activity represents muscle or movement parameters. However, recent studies in non-human primates have shown that neural activity does not simply represent muscle or movement parameters; instead, its temporal structure is well-described by a dynamical system where activity during movement evolves lawfully from an initial pre-movement state. In this study, we analyze neuronal ensemble activity in motor cortex in two clinical trial participants diagnosed with Amyotrophic Lateral Sclerosis (ALS). We find that activity in human motor cortex has similar dynamical structure to that of non-human primates, indicating that human motor cortex contains a similar underlying dynamical system for movement generation. DOI: http://dx.doi.org/10.7554/eLife.07436.00

Reach and grasp by people with tetraplegia using a neurally controlled robotic arm

Paralysis following spinal cord injury (SCI), brainstem stroke, amyotrophic lateral sclerosis (ALS) and other disorders can disconnect the brain from the body, eliminating the ability to carry out volitional movements. A neural interface system (NIS)1–5 could restore mobility and independence for people with paralysis by translating neuronal activity directly into control signals for assistive devices. We have previously shown that people with longstanding tetraplegia can use an NIS to move and click a computer cursor and to control physical devices6–8. Able-bodied monkeys have used an NIS to control a robotic arm9, but it is unknown whether people with profound upper extremity paralysis or limb loss could use cortical neuronal ensemble signals to direct useful arm actions. Here, we demonstrate the ability of two people with long-standing tetraplegia to use NIS-based control of a robotic arm to perform three-dimensional reach and grasp movements. Participants controlled the arm over a broad space without explicit training, using signals decoded from a small, local population of motor cortex (MI) neurons recorded from a 96-channel microelectrode array. One of the study participants, implanted with the sensor five years earlier, also used a robotic arm to drink coffee from a bottle. While robotic reach and grasp actions were not as fast or accurate as those of an able-bodied person, our results demonstrate the feasibility for people with tetraplegia, years after CNS injury, to recreate useful multidimensional control of complex devices directly from a small sample of neural signals