Biology subjects

Lempka, S. F.

Publications and source records attributed to Lempka, S. F..

5 recordsLinked to original sources

bioRxiv2024

High-frequency amplitude-modulated sinusoidal stimulation induces desynchronized yet controllable neural firing

Regaining sensory feedback is critical for people living with limb amputation. Electrical stimulation of sensory fibers in peripheral nerves has been shown to restore focal percepts in the missing limb. However, conventional rectangular current pulses induce sensations often described as unnatural, likely due to the synchronous and periodic nature of activity they evoke. Here we introduce a fast-oscillating amplitude-modulated sinusoidal (FAMS) stimulation waveform that desynchronizes neural activity. Using computational modeling, we show that sinusoidal waveforms evoke asynchronous and irregular firing patterns, with frequency-dependent effects. Leveraging both low- and high-frequency mechanisms, FAMS exploits membrane nonlinearities to enhance neuron-specific differences. In a feline model of peripheral nerve stimulation, FAMS evoked activity that was more asynchronous than conventional rectangular pulses, while remaining easily controllable with simple stimulation parameters. Importantly, in human experiments using noninvasive stimulation of the median nerve, participants reported that FAMS evoked more natural sensations compared to rectangular biphasic pulses in a two-alternative forced-choice task. The preference for FAMS increased at higher intensities above sensory threshold, despite intensity-matched stimulation across waveform types. These findings provide evidence that reduced synchrony in afferent recruitment translates into more naturalistic and comfortable sensory percepts. Together, our results establish FAMS as a promising biomimetic stimulation strategy with potential for clinical applications in sensory feedback restoration. One Sentence SummaryA new electrical stimulation waveform allows for evoking and controlling more naturalistic neural activity than can be achieved with traditional stimulation waveforms.

bioengineering↗

bioRxiv2023

Multiformity of extracellular microelectrode recordings from Aδ neurons in the dorsal root ganglia: A computational modeling study

Microelectrodes serve as a fundamental tool in electrophysiology research throughout the nervous system, providing a means of exploring neural function with a high resolution of neural firing information. We constructed a hybrid computational model using the finite element method and multi-compartment cable models to explore factors that contribute to extracellular voltage waveforms that are produced by sensory pseudounipolar neurons -- specifically, smaller A-type neurons -- and that are recorded by microelectrodes in dorsal root ganglia. The finite element method model included a dorsal root ganglion, surrounding tissues, and a planar microelectrode array. We built a multi-compartment neuron model with multiple trajectories of the glomerular initial segment found in many A-type sensory neurons. Our model replicated both the somatic intracellular voltage profile of A{delta} low-threshold mechanoreceptor neurons and the unique extracellular voltage waveform shapes that are observed in experimental settings. Results from this model indicated that tortuous glomerular initial segment geometries can introduce distinct multiphasic properties into a neurons recorded waveform. Our model also demonstrated how recording location relative to specific microanatomical components of these neurons, and recording distance from these components, can contribute to additional changes in the multiphasic characteristics and peak-to-peak voltage amplitude of the waveform. This knowledge may provide context for research employing microelectrode recordings of pseudounipolar neurons in sensory ganglia, including functional mapping and closed-loop neuromodulation. Further, our simulations gave insight into the neurophysiology of pseudounipolar neurons by demonstrating how the glomerular initial segment aids in increasing the resistance of the stem axon and mitigating rebounding somatic action potentials.

neuroscience↗

bioRxiv2021

Augmented Transcutaneous Stimulation Using an Injectable Electrode

Minimally invasive neuromodulation technologies seek to marry the neural selectivity of implantable devices with the low-cost and non-invasive nature of transcutaneous electrical stimulation (TES). The Injectrode(R) is a needle-delivered electrode that is injected onto neural structures under image guidance. Power is then transcutaneously delivered to the Injectrode using surface electrodes. The Injectrode serves as a low-impedance conduit to guide current to the deep on-target nerve, reducing activation thresholds by an order of magnitude compared to using only surface stimulation electrodes. To minimize off-target recruitment of cutaneous fibers, the energy transfer efficiency from the surface electrodes to the Injectrode must be optimized. TES energy is transferred to the Injectrode through both capacitive and resistive mechanisms. Electrostatic finite element models generally used in TES research consider only the resistive means of energy transfer by defining tissue conductivities. Here, we present an electroquasistatic model, taking into consideration both the conductivity and permittivity of tissue, to understand transcutaneous power delivery to the Injectrode. The model was validated with measurements taken from (n=4) swine cadavers. We used the validated model to investigate system and anatomic parameters that influence the coupling efficiency of the Injectrode energy delivery system. Our work suggests the relevance of electroquasistatic models to account for capacitive charge transfer mechanisms when studying TES, particularly when high-frequency voltage components are present, such as those used for voltage-controlled pulses and sinusoidal nerve blocks.

bioengineering↗

bioRxiv2021

Stimulation of the Dorsal Root Ganglion using an Injectrode

ObjectiveThe goal of this work was to compare afferent fiber recruitment by dorsal root ganglion (DRG) stimulation using an injectable polymer electrode (Injectrode(R)) and a more traditional cylindrical metal electrode. ApproachWe exposed the L6 and L7 DRG in four cats via a partial laminectomy or burr hole. We stimulated the DRG using an Injectrode or a stainless steel electrode using biphasic pulses at three different pulse widths (80, 150, 300 s) and pulse amplitudes spanning the range used for clinical DRG stimulation. We recorded antidromic evoked compound action potentials (ECAPs) in the sciatic, tibial, and common peroneal nerves using nerve cuffs. We calculated the conduction velocity of the ECAPs and determined the charge-thresholds and recruitment rates for ECAPs from A, A{beta}, and A{delta} fibers. We also performed electrochemical impedance spectroscopy measurements for both electrode types. Main ResultsThe ECAP thresholds for the Injectrode did not differ from the stainless steel electrode across all primary afferents (A, A{beta}, A{delta}) and pulse widths; charge-thresholds increased with wider pulse widths. Thresholds for generating ECAPs from A{beta} fibers were 100.0 {+/-} 32.3 nC using the stainless steel electrode, and 90.9 {+/-} 42.9 nC using the Injectrode. The ECAP thresholds from the Injectrode were consistent over several hours of stimulation. The rate of recruitment was similar between the Injectrodes and stainless steel electrode and decreased with wider pulse widths. SignificanceThe Injectrode can effectively excite primary afferents when used for DRG stimulation within the range of parameters used for clinical DRG stimulation. The Injectrode can be implanted through minimally invasive techniques while achieving similar neural activation to conventional electrodes, making it an excellent candidate for future DRG stimulation and neuroprosthetic applications.

bioengineering↗

bioRxiv2019

Realistic Anatomically Detailed Open-Source Spinal Cord Stimulation (RADO-SCS) Model

ObjectiveComputational current flow models of spinal cord stimulation (SCS) are widely used in device development, clinical trial design, and patient programming. Proprietary models of varied sophistication have been developed. An open-source model with state-of-the-art precision would serve as a standard for SCS simulation. ApproachWe developed a sophisticated SCS modeling platform, named Realistic Anatomically Detailed Open-Source Spinal Cord Stimulation (RADO-SCS) model. This platform consists of realistic and detailed spinal cord and ancillary tissues anatomy derived based on prior imaging and cadaveric studies. Represented tissues within the T9-T11 spine levels include vertebrae, intravertebral discs, epidural space, dura, CSF, white-matter, gray-matter, dorsal and ventral roots and rootlets, dorsal root ganglion, sympathetic chain, thoracic aorta, epidural space vasculature, white-matter vasculature, and thorax. As an exemplary, a bipolar SCS montage was simulated to illustrate the model workflow from the electric field calculated from a finite element model (FEM) to activation thresholds predicted for individual axons populating the spinal cord. Main ResultsCompared to prior models, RADO-SCS meets or exceeds detail for every tissue compartment. The resulting electric fields in white and gray-matter, and axon model activation thresholds are broadly consistent with prior stimulations. SignificanceThe RADO-SCS can be used to simulate any SCS approach with both unprecedented resolution (precision) and transparency (reproducibility). Freely available online, the RADO-SCS will be updated continuously with version control.

neuroscience↗