Abstract
The efficacy of spinal cord stimulators is dependent on the ability of the device to functionally activate targeted structures within the spinal cord, while avoiding activation of near-by non-targeted structures. In theory, these objectives can best be achieved by delivering electrical stimuli directly to the surface of the spinal cord. The current experiments were performed to study the influence of different stimulating electrode positions on patterns of spinal cord electrophysiological activation. A custom-designed spinal cord neurostimulator was used to investigate the effects of lead position and stimulus amplitude on cortical electrophysiological responses to spinal cord stimulation. Brain recordings were obtained from subdural grids placed in four adult sheep. We systematically varied the position of the stimulating lead relative to the spinal cord and the voltage delivered by the device at each position, and then examined how these variables influenced cortical responses. A clear relationship was observed between voltage and electrode position, and the magnitude of high gamma-band oscillations. Direct stimulation of the dorsal column contralateral to the grid required the lowest voltage to evoke brain responses to spinal cord stimulation. Given the lower voltage thresholds associated with direct stimulation of the dorsal column, and its possible impact on the therapeutic window, this intradural modality may have particular clinical advantages over standard epidural techniques now in routine use.
Highlights
Two years after Melzak and Wall introduced the gate theory of pain [1] the first use of spinal cord (SC) stimulation (SCS) in a patient with intractable pain was reported by Dr C
Direct SC stimulation evoke brain responses that are qualitatively similar to those observed when stimuli are delivered epidurally? What are the voltage thresholds for electrophysiological activation of spinal cord pathways when the neurostimulator is placed in different positions relative to the spinal cord? How do local brain responses change across the recording grid as we change these parameters? These questions address fundamental issues that are critically important to the design of spinal cord stimulation systems
The current study, did not measure pain scales following spinal cord stimulation in sheep and further studies will be needed to determine if this novel device is capable of overcoming the fundamental limitation of existing spinal cord stimulators for treating chronic refractory pain
Summary
Two years after Melzak and Wall introduced the gate theory of pain [1] the first use of spinal cord (SC) stimulation (SCS) in a patient with intractable pain was reported by Dr C. There is evidence that cerebral activity is altered when the spinal cord is electrically stimulated [5], in such a way as to cause decreased sensory perception and a diminished emotional response to pain [6,7]. Certain of those studies [5,7] employed PET and other functional imaging methods to investigate alterations in BOLD response in the thalamus, posterior parietal, anterior cingulate, as well as prefrontal cortex during spinal cord stimulation. 1–2 year sustained symptom relief has been reported to occur in 25–50% of implanted patients [9,10], and the potential causes for this marked variability in outcomes have been examined extensively
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