Intended Movement Direction Research Articles

514 A Functional Ultrasound Brain-Machine Interface: Real-Time Decoding of Eight Movement Directions

INTRODUCTION: Brain-machine interfaces (BMIs) can be transformative for people living with chronic paralysis. By translating brain signals into computer commands, BMIs can bypass neurological impairments, enabling users to control computers, robots, and more. State-of-the-art BMIs have already made this future a reality in limited clinical trials. However, these BMIs requires inserting highly invasive electrodes into the brain. Device degradation limits longevity to 3-5 years and the field of view of brain activity is small. These factors limit BMI’s widespread adoption. The next generation of BMIs must be longer lasting, less invasive, and scalable. Functional ultrasound neuroimaging (fUSI) is a recently developed technique that meets these criteria. METHODS: We collected data from two nonhuman primates (NHPs). We used real-time fUSI to measure activity in the posterior parietal cortex, an important area for motor planning. We fed this fUSI data into real-time machine learning classifiers to predict the monkey’s intended movement direction and control a behavioral task in real-time. RESULTS: We could predict the monkey’s intended movement direction significantly above chance level (binomial test, p<0.001 for 2- and 8-directions) using the real-time fUSI-BMI. Most direction misclassifications were for neighboring directions (permutation test, p<0.001). The most important voxels for decoding eye movements were within small subpopulations of the lateral intraparietal area (LIP). We found that these LIP subpopulations had a stable encoding of movement direction and the NHPs could accurately control the task more than 40 days after training the decoder model. CONCLUSIONS: This work establishes, for the first time, the feasibility of a real-time ultrasound-based BMI and we have begun translating this work into human applications. This work contributes to the next generation of high-performing, yet minimally-invasive, BMIs that can restore function to patients with neurological impairments.

Implicit Visuomotor Adaptation Remains Limited after Several Days of Training.

Learning in sensorimotor adaptation tasks has been viewed as an implicit learning phenomenon. The implicit process affords recalibration of existing motor skills so that the system can adjust to changes in the body or environment without relearning from scratch. However, recent findings suggest that the implicit process is heavily constrained, calling into question its utility in motor learning and the theoretical framework of sensorimotor adaptation paradigms. These inferences have been based mainly on results from single bouts of training, where explicit compensation strategies, such as explicitly re-aiming the intended movement direction, contribute a significant proportion of adaptive learning. It is possible, however, that the implicit process supersedes explicit compensation strategies over repeated practice sessions. We tested this by dissociating the contributions of explicit re-aiming strategies and the implicit process in human participants over five consecutive days of training. Despite a substantially longer duration of training, the implicit process still plateaued at a value far short of complete learning and, as has been observed in previous studies, was inappropriate for a mirror-reversal task. Notably, we find significant between subject differences that call into question traditional interpretation of these group-level results.

Rehabilitative training system based on a ceiling rail for detecting the intended movement direction of a user.

BACKGROUND:Accurate detection of the intended movement direction of a patient plays an important role in the development of a training system for gait rehabilitation and enables to increase the effect of gait rehabilitation training.OBJECTIVE: This study investigated the detection of the intended movement of a user to operate a ceiling rail-based rehabilitative training system with accurate timing.METHODS: To detect the movement direction intention of a user, two potentiometers were used to measure the movement direction in the anterior, posterior, and left and right directions of the user when operating the driving motor of the rehabilitative training system. A simple test mock-up with two potentiometers was fabricated, and the experiments were conducted to determine the effect of the direction of movement on the measured values of potentiometers. A direction measurement algorithm was developed to control the driving motor of the rail-based gait rehabilitative training system.RESULTS: The intended movement direction of the user could be predicted for eight directions by combining the “positive value, 0, negative value” of each measured value of the two potentiometers. Further, the developed algorithm was effectively used to control the driving function to assist the walking, sitting–standing, and climbing up–down the step activities in daily life.CONCLUSIONS: The movement intention detection function for users developed in this paper can be used to effectively control a rehabilitative training system for patients with hemiplegia to improve gait movement and posture balance, thereby improving their function of activities of daily living.

Pushing attention to one side: Force field adaptation alters neural correlates of orienting and disengagement of spatial attention.

Sensorimotor adaptation to wedge prisms can alter the balance of attention between left and right space in healthy adults, and improve symptoms of spatial neglect after stroke. Here we asked whether the orienting of spatial attention to visual stimuli is affected by a different form of sensorimotor adaptation that involves physical perturbations of arm movement, rather than distortion of visual feedback. Healthy participants performed a cued discrimination task before and after they made reaching movements to a central target. A velocity-dependent force field pushed the hand aside during each reach, and required participants to apply compensatory forces toward the opposite side. We used event-related potentials (ERPs) to determine whether electroencephalography (EEG) responses reflecting orienting (cue-locked N1) and disengagement (target-locked P1) of spatial attention are affected by adaptation to force fields. After adaptation, the cue-locked N1 was relatively larger for stimuli presented in the hemispace corresponding to the direction of compensatory hand force. P1 amplitudes evoked by invalidly cued targets presented on the opposite side were reduced. This suggests that force field adaptation boosted attentional orienting responses toward the side of hand forces, and impeded attentional disengagement from that side, mimicking previously reported effects of prism adaptation. Thus, remapping between motor commands and intended movement direction is sufficient to bias ERPs, reflecting changes in the orienting of spatial attention in the absence of visuo-spatial distortion or visuo-proprioceptive mismatch. Findings are relevant to theories of how sensorimotor adaptation can modulate attention, and may open new avenues for treatment of spatial neglect.

Application mapping to mesh NoCs using a Tabu-search based swarm optimization

A hybrid optimization scheme is presented that combines Tabu-search, communication volume based core swapping and Discrete Particle Swarm Optimization (DPSO) for NoC (Network-on-Chip) mapping. The main goal of the optimization is to map an application core-graph such that the overall communication latency of the NoC is minimal. It is assumed that the target NoC has a 2D-mesh topology. DPSO is used as the main optimization technique where each swarm particle move is influenced by the global and local best, previous visited search space locations, and a deterministic method to reduce communication volume of existing mapping. We employ a Tabu-list to discourage swarm particles to re-visit the explored search space and propose an alternative direction towards the intended movement direction. The methodology is tested for some multimedia applications as well as randomly generated large network of synthetic cores-graphs. For larger applications, our hybrid scheme generates high quality NoC mapping solutions as compared to DPSO based existing techniques.

Communication and Inference of Intended Movement Direction during Human-Human Physical Interaction.

Of particular interest to the neuroscience and robotics communities is the understanding of how two humans could physically collaborate to perform motor tasks such as holding a tool or moving it across locations. When two humans physically interact with each other, sensory consequences and motor outcomes are not entirely predictable as they also depend on the other agent’s actions. The sensory mechanisms involved in physical interactions are not well understood. The present study was designed (1) to quantify human–human physical interactions where one agent (“follower”) has to infer the intended or imagined—but not executed—direction of motion of another agent (“leader”) and (2) to reveal the underlying strategies used by the dyad. This study also aimed at verifying the extent to which visual feedback (VF) is necessary for communicating intended movement direction. We found that the control of leader on the relationship between force and motion was a critical factor in conveying his/her intended movement direction to the follower regardless of VF of the grasped handle or the arms. Interestingly, the dyad’s ability to communicate and infer movement direction with significant accuracy improved (>83%) after a relatively short amount of practice. These results indicate that the relationship between force and motion (interpreting as arm impedance modulation) may represent an important means for communicating intended movement direction between biological agents, as indicated by the modulation of this relationship to intended direction. Ongoing work is investigating the application of the present findings to optimize communication of high-level movement goals during physical interactions between biological and non-biological agents.

Responses in posterior parietal cortex to movement intention task with visual and tactile cues.

Posterior parietal cortex (PPC) is considered to be related to forming of motor intention. The detection of the direction intended movements and the type of intended movement is a challenging goal in neuroscience and engineering applications such as brain-computer interfacing (BCI). In previous studies, it has been reported that EEG signals extracted from PPC can be used to decode intended movement direction. However, it is not clear whether extracted EEG signals are related to motor intention, because visually evoked potential (VEP) which evoked by visual cue in their experiment may be included in their extracted EEG signals. The purpose of this study is to investigate the possibility of VEP mixed into extracted EEG signals. Therefore experiments with not only visual but also tactile cues were conducted. EEG components that could be related to PPC were extracted by using independent component analysis (ICA). We compared event related potential (ERP) waveforms between two experiments. In the result, ERP waveforms of the experiment with tactile cue were significantly different from that of the experiment with visual cue. This result suggests that VEP was included in the EEG signals extracted from PPC in the experiment with visual cue.

Reprint of “Non-causal spike filtering improves decoding of movement intention for intracortical BCIs”

BackgroundMultiple types of neural signals are available for controlling assistive devices through brain–computer interfaces (BCIs). Intracortically recorded spiking neural signals are attractive for BCIs because they can in principle provide greater fidelity of encoded information compared to electrocorticographic (ECoG) signals and electroencephalograms (EEGs). Recent reports show that the information content of these spiking neural signals can be reliably extracted simply by causally band-pass filtering the recorded extracellular voltage signals and then applying a spike detection threshold, without relying on “sorting” action potentials. New methodWe show that replacing the causal filter with an equivalent non-causal filter increases the information content extracted from the extracellular spiking signal and improves decoding of intended movement direction. This method can be used for real-time BCI applications by using a 4ms lag between recording and filtering neural signals. ResultsAcross 18 sessions from two people with tetraplegia enrolled in the BrainGate2 pilot clinical trial, we found that threshold crossing events extracted using this non-causal filtering method were significantly more informative of each participant's intended cursor kinematics compared to threshold crossing events derived from causally filtered signals. This new method decreased the mean angular error between the intended and decoded cursor direction by 9.7° for participant S3, who was implanted 5.4 years prior to this study, and by 3.5° for participant T2, who was implanted 3 months prior to this study. ConclusionsNon-causally filtering neural signals prior to extracting threshold crossing events may be a simple yet effective way to condition intracortically recorded neural activity for direct control of external devices through BCIs.

Human place and response learning: navigation strategy selection, pupil size and gaze behavior

In this study, we examined the cognitive processes and ocular behavior associated with on-going navigation strategy choice using a route learning paradigm that distinguishes between three different wayfinding strategies: an allocentric place strategy, and the egocentric associative cue and beacon response strategies. Participants approached intersections of a known route from a variety of directions, and were asked to indicate the direction in which the original route continued. Their responses in a subset of these test trials allowed the assessment of strategy choice over the course of six experimental blocks. The behavioral data revealed an initial maladaptive bias for a beacon response strategy, with shifts in favor of the optimal configuration place strategy occurring over the course of the experiment. Response time analysis suggests that the configuration strategy relied on spatial transformations applied to a viewpoint-dependent spatial representation, rather than direct access to an allocentric representation. Furthermore, pupillary measures reflected the employment of place and response strategies throughout the experiment, with increasing use of the more cognitively demanding configuration strategy associated with increases in pupil dilation. During test trials in which known intersections were approached from different directions, visual attention was directed to the landmark encoded during learning as well as the intended movement direction. Interestingly, the encoded landmark did not differ between the three navigation strategies, which is discussed in the context of initial strategy choice and the parallel acquisition of place and response knowledge.

Volitional control of single cortical neurons in a brain–machine interface

Volitional control of cortical activity is relevant for optimizing control signals for neuroprosthetic devices. We explored the control of firing rates of single cortical cells in two Macaca nemestrina monkeys by providing visual feedback of neural activity and rewarding changes in cell rates. During ‘brain-control’ sessions, the monkeys modulated the activity of each of 246 cells to acquire targets requiring high or low discharge rates. Cell control improved more than two-fold from the beginning of practice to peak performance. Cell activity was modulated substantially more during brain control than during wrist movements. When recording stability permitted, the monkeys practiced controlling activity of the same cells across multiple days. The performance improved substantially for 27 of 36 cells when practicing brain control across days. The monkeys maintained discharge rates within each target for 1 s, but could maintain rates for up to 3 s for some cells, and performed the brain-control task equally well using cells recorded from the pre-central cortex compared to cells in the post-central cortex, and independently of any directional tuning. These findings demonstrate that arbitrary single cortical neurons, regardless of the strength of directional tuning, are capable of controlling cursor movements in a one-dimensional brain–machine interface. It is possible that direct conversion of activity from single cortical cells to control signals for neuroprosthetic devices may be a useful complementary strategy to population decoding of the intended movement direction.

Decoding and Cortical Source Localization for Intended Movement Direction With MEG

Magnetoencephalography (MEG) enables a noninvasive interface with the brain that is potentially capable of providing movement-related information similar to that obtained using more invasive neural recording techniques. Previous studies have shown that movement direction can be decoded from multichannel MEG signals recorded in humans performing wrist movements. We studied whether this information can be extracted without overt movement of the subject, because the targeted users of brain-controlled interface (BCI) technology are those with severe motor disabilities. The objectives of this study were twofold: 1) to decode intended movement direction from MEG signals recorded during the planning period before movement onset and during imagined movement and 2) to localize cortical sources modulated by intended movement direction. Ten able-bodied subjects performed both overt and imagined wrist movement while their cortical activities were recorded using a whole head MEG system. The intended movement direction was decoded using linear discriminant analysis and a Bayesian classifier. Minimum current estimation (MCE) in combination with a bootstrapping procedure enabled source-space statistical analysis, which showed that the contralateral motor cortical area was significantly modulated by intended movement direction, and this modulation was the strongest ∼100 ms before the onset of overt movement. These results suggest that it is possible to study cortical representation of specific movement information using MEG, and such studies may aid in presurgical localization of optimal sites for implanting electrodes for BCI systems.

Transformation of the intended direction of movement during continuous motor trajectories.

Chronometric and neurophysiological studies have demonstrated that mentally transforming the intended direction of a pointing movement is a time-consuming process, the duration of which increases with the angle of rotation. If the same time-consuming process occurred while tracing a curved trajectory, it would affect the time course of the movement. The data from subjects drawing simple figures match well the predictions made, and support the hypothesis that a time-consuming process of transformation of the intended movement direction operates during the production of continuous trajectories. This biologically inspired hypothesis provides a functional explanation for the relation between speed of the movement and curvature of the path. In addition, it contrasts with the view of continuous movements as essentially oscillatory motions.

Neuronal activity in primate parietal cortex area 5 varies with intended movement direction during an instructed-delay period.

A monkey was trained to make arm movements to visual targets immediately after presentation of a GO signal, either in a visual reaction-time paradigm (CONTROL task), or after an instructed-delay period of variable duration, during which a CUE stimulus signalled the direction of the impending movement (DELAY task). The activity of 98 area 5 cells recorded in 2 hemispheres varied with movement direction in the CONTROL task. This included 60 "early" cells which showed directional activity changes prior to movement onset. In the DELAY task, 54/98 cells (55%) showed activity changes during the instructed-delay period which varied with the direction of the impending movement. Most of these (45/54, 83%) were "early" cells. Forty proximal arm-related cells were recorded in adjacent area 2. In contrast to area 5, only 2/40 area 2 cells showed any evidence of changes in activity varying with intended movement direction during the instructed-delay period. The origin of area 5 activity changes during an instructed-delay period which are related to intended direction of a delayed movement is uncertain, but its presence is consistent with a number of proposed roles for area 5.