Patients, doctors and researchers look with great expectations to epidural electrostimulation, a medical technique that could alleviate the condition of subjects affected by paralysis due to spinal cord injury. Although still relatively rudimentary, the technique is constantly being improved thanks to research. A group of scientists, have published a paper in the journal Spinal Cord, proposing a new methodological approach based on distributing the stimulation and modulating the frequency of electrical impulses, which has provided good results in vitro.
Epidural electrostimulation is a medical technique that has been used for several years now to help patients affected by paralysis due to a spinal cord injury. It involves implanting electrodes over the dorsal nerve roots (which convey incoming “sensory” inputs) of the spinal cord below the level of the trauma and applying electrical stimuli of varying intensity and frequency. This technique, which produces or helps produce activation patterns of the motor nerves (ventral, outgoing) has shown promising results, and the scientists hope that one day it will be able to help paralysed people, for example, to stand and take a few steps, as well as restoring sphincter control and sexual function.
There is still a long way to go before reaching that goal, and for this reason the scientific community is redoubling efforts to refine the method. “Most research to date has focused on the materials and technology of the devices. Our study, by contrast, looked at the nature and quality of the electrical signal delivered by the electrodes”, explains Giuliano Taccola, researcher at the International School for Advanced Studies (SISSA) of Trieste and coordinator of the study. “The question everyone is asking is always the same: how do we get effective motor responses? In this sense, we believe it’s important to better modulate the electrical signal and precisely identify the points where it should be applied”.
“Current techniques consist of applying a high-frequency signal in a generalized fashion. That way, we get a ‘cumulative’ and somewhat undifferentiated stimulation of a group of nerve fibres. What we did instead was to adopt a ‘multi-site’ approach: the electrical stimulation is applied at different points of the circuit”, he explains. In the study, Taccola and colleagues worked with spinal neural circuits prepared in vitro. This allowed them to control the simulation sites very carefully, and to record the network responses with great precision.
“The other novelty we introduced was to use a low-frequency stimulation”. The combination of these two factors (signal frequency and multiple sites) produced very efficient motor patterns. “With our work we have defined a new spinal cord stimulation strategy for the activation of motor neurons, which may also be imported in many of the stimulators being used in clinical settings”.
The first author of the study, carried out in collaboration with the SPINAL laboratory at the Institute of Physical Medicine and Rehabilitation (IMFR) of the Gervasutta Hospital in Udine (where the experimental data were collected) and the Catholic University of Leuven in Belgium, is Francesco Dose, a young PhD student at SISSA.
NeuroscienceNews.com would like to thank SISSA for submitting this news article.
Source: SISSA
Image Credit: The image is credited to SISSA and is licensed CC BY-NC-SA 2.0
Original Research: Abstract for “Staggered multi-site low-frequency electrostimulation effectively induces locomotor patterns in the isolated rat spinal cord” by F Dose, R Deumens, P Forget and G Taccola in Spinal Cord. Published online June 23 2015 doi:10.1038/sc.2015.106
Abstract
Staggered multi-site low-frequency electrostimulation effectively induces locomotor patterns in the isolated rat spinal cord
Study design: Experimental animal study.
Objectives: Epidural stimulation has been used to activate locomotor patterns after spinal injury and typically employs synchronous trains of high-frequency stimuli delivered directly to the dorsal cord, thereby recruiting multiple afferent nerve roots. Here we investigate how spinal locomotor networks integrate multi-site afferent input and address whether frequency coding is more important than amplitude to activate locomotor patterns.
Setting: Italy and Belgium.
Methods: To investigate the importance of input intensity and frequency in eliciting locomotor activity, we used isolated neonatal rat spinal cords to record episodes of fictive locomotion (FL) induced by electrical stimulation of single and multiple dorsal roots (DRs), employing different stimulating protocols.
Results: FL was efficiently induced through staggered delivery (delays 0.5 to 2 s) of low-frequency pulse trains (0.33 and 0.67 Hz) to three DRs at intensities sufficient to activate ventral root reflexes. Delivery of the same trains to a single DR or synchronously to multiple DRs remained ineffective. Multi-site staggered trains were more efficient than randomized pulse delivery. Weak trains simultaneously delivered to DRs failed to elicit FL. Locomotor rhythm resetting occurred with single pulses applied to various distant DRs.
Conclusion: Electrical stimulation recruited spinal networks that generate locomotor programs when pulses were delivered to multiple sites at low frequency. This finding might help devising new protocols to optimize the increasingly more common use of epidural implantable arrays to treat spinal dysfunctions.
“Staggered multi-site low-frequency electrostimulation effectively induces locomotor patterns in the isolated rat spinal cord” by F Dose, R Deumens, P Forget and G Taccola in Spinal Cord. Published online June 23 2015 doi:10.1038/sc.2015.106
