Mechanism of Spinal Cord and Peripheral Nerve Stimulation: More than the Gate Control Theory

Abstract

The use of electricity for the treatment of pain has been around since ancient times. It was not until the second half of the 20th century with the advent of the gate control theory that an explanation for its effects was put forward [1]. In the time since the postulation of this theory, there have been several advances using animal models of pain and neuromodulation that are shedding more light into the neurobiology of electrical stimulation for pain. The work has revealed that there are more mechanisms and areas of the nervous system involved in the effects of electrical stimulation than what would be predicted by the gate control theory. Higher brain centers are activated when stimulation is applied to the dorsal columns as in spinal cord stimulation [2]. Likewise, SCS influences peripheral targets by antidromic pulses traveling in the dorsal columns and into peripheral afferents [3]. These same pulses can influence intrinsic pain process in the dorsal horn by modulating the release of different neurotransmitters [4] (Figure 1). The mechanisms behind the effects of subcutaneous electrical stimulation are much less understood than the mechanisms for SCS. The lack of animal models necessary to study mechanisms has hindered this understanding until recently. A novel model of SQS has been developed in rodents and this model has proven to mimic some of the aspects of clinical practice. When compared with a rodent model of transcutaneous electrical nerve stimulation (TENS), the SQS model presented with differential effects than the TENS model, suggesting the involvement of different mechanism of action between these two neuromodulation therapies [5]. Future studies will concentrate in investigating optimal parameters of stimulation with the SQS model.