Biology subjects

Dalrymple, A. N.

Publications and source records attributed to Dalrymple, A. N..

4 recordsLinked to original sources

bioRxiv2022

High-Frequency Stimulation Does Not Improve Comfort of Transcutaneous Spinal Cord Stimulation

Spinal cord neuromodulation has gained much attention for demonstrating improved motor recovery in people with spinal cord injury, motivating the development of clinically applicable technologies. Among them, transcutaneous spinal cord stimulation (tSCS) is attractive because of its non-invasive profile. Many tSCS studies employ a high-frequency (10 kHz) carrier, which has been reported to reduce stimulation discomfort. However, these claims have come under scrutiny in recent years. The purpose of this study was to determine whether high-frequency tSCS is more comfortable at therapeutic amplitudes, which evoke posterior root-muscle (PRM) reflexes. In 16 neurologically intact participants, tSCS was delivered using a 1-ms long monophasic pulse with and without a high-frequency carrier. Stimulation amplitude and pulse duration were varied and PRM reflexes were recorded from the soleus, gastrocnemius, and tibialis anterior muscles. Participants rated their discomfort during stimulation from 0-10 at PRM reflex threshold. At PRM reflex threshold, high-frequency stimulation (0.87 {+/-} 0.2) was equally comfortable as conventional stimulation (1.03 {+/-} 0.18) but required approximately double the charge to evoke the PRM reflex (conventional: 32.4 {+/-} 9.2 {micro}C; high-frequency: 62.5 {+/-} 11.1 {micro}C). Strength-duration curves for high-frequency stimulation had a rheobase that was 4.8X greater and a chronaxie that was 5.7X narrower than the conventional monophasic pulse, indicating that high-frequency stimulation was less efficient in recruiting neural activity in spinal roots. High-frequency tSCS is equally as comfortable as conventional stimulation at amplitudes required to stimulate spinal dorsal roots. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=178 SRC="FIGDIR/small/506783v1_ufig1.gif" ALT="Figure 1"> View larger version (33K): org.highwire.dtl.DTLVardef@f013f3org.highwire.dtl.DTLVardef@1aded5eorg.highwire.dtl.DTLVardef@1bad2e0org.highwire.dtl.DTLVardef@6aaf96_HPS_FORMAT_FIGEXP M_FIG C_FIG

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

Pavlovian Control of Intraspinal Microstimulation to Produce Over-Ground Walking

ObjectiveNeural interface technologies are more commonly used in people with neural injury. To achieve a symbiotic relationship between device and user, the control system of the device must augment remaining function and adapt to day-to-day changes. The goal of this study was to develop predictive control strategies to produce alternating, over-ground walking in a cat model of hemisection spinal cord injury (SCI) using intraspinal microstimulation (ISMS).\n\nApproachEight cats were anaesthetized and placed in a sling over a walkway. The residual function of a hemisection SCI was mimicked by manually moving one hind-limb through the walking cycle over the walkway. ISMS targeted motor networks in the lumbosacral enlargement to activate muscles in the other limb using low levels of current (< 130 {micro}A). Four different people took turns to move the \"intact\" limb. Two control strategies, which used ground reaction force and angular velocity information about the manually moved limb to control the timing of the transitions of the other limb, were compared. The first strategy, reaction-based control, used thresholds on the sensor values to initiate state transitions. The other strategy used a reinforcement learning strategy, Pavlovian control, to learn predictions about the sensor values. Thresholds on the predictions were used to initiate transitions.\n\nMain ResultsBoth control strategies were able to produce alternating, over-ground walking. Reaction-based control required manual tuning of the thresholds for each person to produce walking, whereas Pavlovian control did not. We demonstrate that learning occurs quickly during walking. Predictions of the sensor signals were learned quickly, initiating transitions in no more than 4 steps. Pavlovian control was resilient to transitions between people walking the limb, between cat experiments, and recovered from mistakes during walking.\n\nSignificanceThis work demonstrates that Pavlovian control can augment remaining function and allow for personalized walking with minimal tuning requirements.

bioengineering↗