Effective control of chronic pain is a top priority in the United States, as approximately 10% of adults have severe chronic pain - most of which is chronic lower back pain (CLBP). However, despite the advances in neuroscience over the past 20 years, chronic pain is largely treated with opiate narcotics, much as was done in the Civil War. In addition to their high abuse liability and dependence potential, only 30-40% of chronic pain patients declare they receive satisfactory (\>50%) relief from their pain through pharmacological treatment. In these patients a common clinical practice is to escalate the dose of opiates as tolerance develops - which unfortunately has contributed to escalation in opiate overdose deaths, a resurgence of intravenous heroin use, and $55 billion in societal costs. Consequently there is a critical need for new, treatments that can treat pain and reduce reliance on opiates in individuals with chronic pain.
The goal of this proposal is to evaluate 2 novel non-invasive brain stimulation strategies to mitigate pain and the brain's response to pain in CLBP patients that are currently taking chronic opiates, or that are seeking an alternative treatment for pain. Transcranial Magnetic Stimulation (TMS), can induce long term potentiation (LTP-like) and long term depression (LTD-like) effects on brain activity in a frequency dependent manner. Our group has previously demonstrated that LTP-like TMS to the dorsolateral prefrontal cortex (DLPFC, a node in the Executive Control Network (ECN)) can decrease perceived pain and corresponding blood oxygen level dependent (BOLD) signal in the "Pain Network'. The Pain Network is an expansion of the Salience Network (SN; insula, dorsal anterior cingulate) which includes the thalamus and somatosensory cortex. The analgesic effects of DLPFC TMS can be blocked by naloxone - suggesting that the analgesic effects of LTP-like DLPFC TMS are opiate mediated. Additionally, DLPFC TMS delivered postoperatively leads to less patient administered morphine use (PCA-pump) in the hospital and less opiate use in the outpatient setting. These data all suggest that LTP-like DLPFC TMS is a promising candidate for treating pain.
An alternative strategy is to apply LTD-like stimulation to the medial prefrontal cortex (LTD-like mPFC rTMS. This strategy is based on our understanding of functional neural architecture, wherein the SN is modulated by 2 other core networks: the executive control network (ECN) and the default mode network (DMN). As stated above, it is possible to attenuate activity in the SN through LTP-like TMS to the DLPFC, a node in the ECN. It is also possible to attenuate the SN through LTD-like TMS to the ventral medial prefrontal cortex (a node in the DMN). The proposed study will be the first to employ a randomized, double-blind, sham-controlled design to parametrically evaluate the longitudinal effects of 16 days of rTMS to the MC or the MPFC on self-reported pain and the brain's response to pain. This will be done in a cohort of patients recruited from the community as well as WFBH clinics with chronic lower back pain that have not been able to find adequate pain relief, whether or not they are using prescription opiates for 3 or more months. Participants will be randomized to receive rTMS to the MC, MPFC, or sham (50% at each site), using a Latin square randomization. Resting state connectivity will be collected 3 times: before the 1st day of TMS, after the 12th day of TMS, and before the 16th day of TMS (the last day administered).
Aim 1. Evaluate MC rTMS as a tool to dampen pain and the engagement of the Pain Network. Hypothesis 1: MC TMS will attenuate the baseline brain response to pain (Pain Network activity) and increase activity in the ECN when the patient is given instructions to 'control' the pain.
Aim 2. Evaluate MPFC rTMS as a tool to dampen pain and the engagement of the Pain Network. Hypothesis 1: MPFC TMS will also attenuate the baseline brain response to pain (Pain Network activity) but will not effect the ECN or SN when the patient is given instructions to 'control' the pain.
(Exploratory Aim): The investigator will evaluate if there are rate-dependent effects between baseline SN connectivity with the ECN and DMN and the efficacy of each TMS strategy on subjective pain. Data will be analyzed by using multivariate pattern analysis (MVPA). While the primary outcomes will be magnetic resonance imaging (MRI) Visit 1 versus Visit 2, the investigator will also examine the relative 'durability' of the effects on pain by comparing the MRI data at the end of all TMS visits between and within groups with factor analysis.
The relative efficacy of these strategies will directly translate to development of a large clinical trial investigating rTMS as an innovative, new treatment option for pain in patients with CLBP.
