Biomedical subjects

Douglas J Weber

Publications and source records attributed to Douglas J Weber.

7 recordsLinked to original sources

PubMed2006

Method for counting motor units in mice and validation using a mathematical model.

Weakness and atrophy are clinical signs that accompany muscle denervation resulting from motor neuron disease, peripheral neuropathies, and injury. Advances in our understanding of the genetics and molecular biology of these disorders have led to the development of therapeutic alternatives designed to slow denervation and promote reinnervation. Preclinical in vitro research gave rise to the need of a method for measuring the effects in animal models. Our goal was to develop an efficient method to determine the number of motor neurons making functional connections to muscle in a transgenic mouse model of amyotrophic lateral sclerosis (ALS). We developed a novel protocol for motor unit number estimation (MUNE) using incremental stimulation. The method involves analysis of twitch waveforms using a new software program, ITS-MUNE, designed for interactive calculation of motor unit number. The method was validated by testing simulated twitch data from a mathematical model of the neuromuscular system. Computer simulations followed the same stimulus-response protocol and produced waveform data that were indistinguishable from experiments. We show that our MUNE protocol is valid, with high precision and small bias across a wide range of motor unit numbers. The method is especially useful for large muscle groups where MUNE could not be done using manual methods. The results are reproducible across naïve and expert analysts, making it suitable for easy implementation. The ITS-MUNE analysis method has the potential to quantitatively measure the progression of motor neuron diseases and therefore the efficacy of treatments designed to alleviate pathologic processes of muscle denervation.

Algorithms↗

PubMed2006

Brain-controlled interfaces: movement restoration with neural prosthetics.

Brain-controlled interfaces are devices that capture brain transmissions involved in a subject's intention to act, with the potential to restore communication and movement to those who are immobilized. Current devices record electrical activity from the scalp, on the surface of the brain, and within the cerebral cortex. These signals are being translated to command signals driving prosthetic limbs and computer displays. Somatosensory feedback is being added to this control as generated behaviors become more complex. New technology to engineer the tissue-electrode interface, electrode design, and extraction algorithms to transform the recorded signal to movement will help translate exciting laboratory demonstrations to patient practice in the near future.

Algorithms↗

PubMed2006

Decoding sensory feedback from firing rates of afferent ensembles recorded in cat dorsal root ganglia in normal locomotion.

Sensory feedback is required by biological motor control systems to maintain stability, respond to perturbations, and adapt. Similarly, motor neuroprostheses require feedback to provide natural and complete restoration of motor functions. In this paper, we show that ensemble firing rates from the body's mechanoreceptors can provide a natural source of kinematic state feedback and could be useful for prosthetic control. Single unit recordings from multiple primary afferent neurons were obtained during walking using multichannel electrode arrays implanted chronically in the L7 dorsal root ganglia of three cats. We typically recorded simultaneously from over 20-30 neurons during the first 7-14 days after surgery, but recordings gradually worsened thereafter. Histology indicates that a ring of inflammatory and connective tissues (100 microm thick) develops around each microelectrode and likely contributes to the degradation in recording quality. Accurate estimates of the hindlimb trajectory were made using a linear filter with inputs from only a few neurons highly correlated with limb kinematics. The coefficients for the linear filter were identified in a least-squares fit with 5-10 s of walking data (model training stage). The estimated and actual trajectories of separate walking data generally match well for walking at a range of speeds accounting for 63 +/- 22% (mean +/- S.D. for hip, knee, and ankle) of the variance in joint angle and 72 +/- 4% of the variance in joint angular velocities. These results indicate that a neural interface with primary sensory neurons in the dorsal root ganglion can provide accurate kinematic state information that may be useful for closed loop control of a neuroprosthesis.

Action Potentials↗

PubMed2005

BIONic WalkAide for correcting foot drop.

The goal of this study was to test the feasibility and efficacy of using microstimulators (BIONs) to correct foot drop, the first human application of BIONs in functional electrical stimulation (FES). A prototype BIONic foot drop stimulator was developed by modifying a WalkAide2 stimulator to control BION stimulation of the ankle dorsiflexor muscles. BION stimulation was compared with surface stimulation of the common peroneal nerve provided by a normal WalkAide2 foot drop stimulator. Compared to surface stimulation, we found that BION stimulation of the deep peroneal nerve produces a more balanced ankle flexion movement without everting the foot. A three-dimensional motion analysis was performed to measure the ankle and foot kinematics with and without stimulation. Without stimulation, the toe on the affected leg drags across the ground. The BIONic WalkAide elevates the foot such that the toe clears the ground by 3 cm, which is equivalent to the toe clearance in the unaffected leg. The physiological cost index (PCI) was used to measure effort during walking. The PCI is high without stimulation (2.29 +/- 0.37; mean +/- S.D.) and greatly reduced with surface (1.29 +/- 0.10) and BION stimulation (1.46 +/- 0.24). Also, walking speed is increased from 9.4 +/- 0.4 m/min without stimulation to 19.6 +/- 2.0 m/min with surface and 17.8 +/- 0.7 m/min with BION stimulation. We conclude that functional electrical stimulation with BIONs is a practical alternative to surface stimulation and provides more selective control of muscle activation.

Adult↗

PubMed2004

Editing trains of action potentials from multi-electrode arrays.

When recording from multi-electrode arrays, only a short period around the time of a threshold crossing is generally saved for later analysis. Then, waveforms are often sorted automatically to identify templates of spikes from individual neurons near an electrode. As spikes sum from different neurons and noise is present, some spikes may be missed and others erroneously accepted. This paper describes methods for identifying and correcting errors in recorded spike trains to recover the pattern of spikes from each neuron as faithfully as possible. These methods are complementary to, but distinct from methods to reconstruct waveforms that arise from summation of individual templates that overlap one another. Our methods are based on the local statistics of the firing rates or inter-spike intervals and the methods work best for neurons that fire regularly (small standard deviation relative to the mean interval). First, we test whether accepting more spikes, whose waveforms are close to the templates that have been identified, will increase the regularity or smoothness of the firing rates. Then, after accepting spikes that increase regularity, we test whether individual intervals are sufficiently longer (or shorter) than their neighbors to identify spikes that have been omitted (or accepted) erroneously. The methods are tested on simulated spike trains, where spikes have been inserted or deleted at random, and on spike trains recorded from multi-electrode arrays in dorsal root ganglia of cats walking on a treadmill.

Action Potentials↗

PubMed2004

Adaptive behavior of cortical neurons during a perturbed arm-reaching movement in a nonhuman primate.

This chapter provides evidence of spatial and temporal changes in the behavior of neurons within Areas 5 and 4 of the sensorimotor cortex of a nonhuman primate while it was executing a perturbed arm-reaching task. Chronically implanted electrode arrays were used to record simultaneously from 37 to 58 neurons. Also measured were the trajectory of arm movement, EMG activity in selected arm muscles and the perturbation force applied to the arm. The adaptation in Area 4 neurons' behavior usually involved a reduction in the latency from the onset of the perturbation to the peak-firing rate of the cell. In contrast, Area 5 neurons exhibited no such adaptive change in this latency. In each cortical area, the adaptation was not uniform across all neurons, and the spatial pattern of neuronal population behavior changed over the period of behavioral adaptation. We also found that the direction of arm movement and its configuration were important in determining which control strategy (predictive trajectory compensation or stiffness control) the animal used to overcome the externally applied perturbation for an improved performance of the reaching task.

Adaptation, Physiological↗

PubMed2003

The role of vision on hand preshaping during reach to grasp.

During reaching to grasp objects with different shapes hand posture is molded gradually to the object's contours. The present study examined the extent to which the temporal evolution of hand posture depends on continuous visual feedback. We asked subjects to reach and grasp objects with different shapes under five vision conditions (VCs). Subjects wore liquid crystal spectacles that occluded vision at four different latencies from onset of the reach. As a control, full-vision trials (VC5) were interspersed among the blocked vision trials. Object shapes and all VCs were presented to the subjects in random order. Hand posture was measured by 15 sensors embedded in a glove. Linear regression analysis, discriminant analysis, and information theory were used to assess the effect of removing vision on the temporal evolution of hand shape. We found that reach duration increased when vision was occluded early in the reach. This was caused primarily by a slower approach of the hand toward the object near the end of the reach. However, vision condition did not have a significant effect on the covariation patterns of joint rotations, indicating that the gradual evolution of hand posture occurs in a similar fashion regardless of vision. Discriminant analysis further supported this interpretation, as the extent to which hand posture resembled object shape and the rate at which hand posture discrimination occurred throughout the movement were similar across vision conditions. These results extend previous observations on memory-guided reaches by showing that continuous visual feedback of the hand and/or object is not necessary to allow the hand to gradually conform to object contours.

Adult↗