Non-invasive insular stimulation for peripheral neuropathic pain: Influence of target or symptom?

OBJECTIVES: The posterior-superior insula (PSI) has been shown to be a safe and potentially effective target for neuromodulation in peripheral neuropathic pain (PNP) in humans and animal models. However, it remains unknown whether there is a measurable responder profile to PSI stimulation. Two factors were hypothesized to influence the response of repetitive transcranial magnetic stimulation (rTMS) of the PSI: differences in rTMS target (discrete subregions of the PSI) or PNP phenotype. METHODS: This is a secondary analysis from a randomized, double-blind, sham-controlled, cross-over trial assessing PSI-rTMS in PNP (N = 31, 5 days rTMS) (10.1016/j.neucli.2021.06.003). Active PSI-rTMS true responders (>50% pain reduction from baseline after active but not after sham series of treatment) were compared with not true responders, to determine whether they differed with respect to 1) rTMS neuro-navigational target coordinates, and/or 2) specific neuropathic pain symptom inventory (NPSI) clusters (pinpointed pain, evoked pain, and deep pain) at baseline. RESULTS: Mean rTMS target coordinates did not differ between true (n = 45.1%) and not true responders (p = 0.436 for X, p = 0.120 for Y, and p = 0.116 for Z). The Euclidian distance between true and not true responders was 4.04 mm. When comparing differences in responders between NPSI clusters, no participant within the evoked pain cluster was a true responder (p = 0.024). CONCLUSION: Response to PSI-rTMS may depend on pain cluster subtype rather than on differences in targeting within the PSI.

Altered Functional Connectivity Between Precuneus and Motor Systems in Parkinson's Disease Patients.

Parkinson's disease (PD) is a neurodegenerative disorder that affects motor skills and cognition. As brain structure and function are compromised, functional magnetic resonance imaging (fMRI) can be a helpful tool to further investigate how intrinsic connectivity is impaired on the disease. The precuneus and medial prefrontal cortex (mPFC) are hub regions involved on the default mode network (DMN), a system that is active during rest and related to cognitive processes. We hypothesized that PD patients would present a decrease in functional connectivity among these two regions and the rest of the brain. Our goal was to identify regions in which functional connectivity to precuneus and mPFC was altered in PD. This study was based on resting-state fMRI data from 37 healthy subjects and 55 PD patients. Precuneus and mPFC were selected as seed regions in a whole brain functional connectivity mapping. As expected, we found abnormal connectivity from precuneus to motor system regions in PD patients, pointing toward a decreased connectivity in the disease. No significant group effects were found for the mPFC. Our findings suggest that internetwork connectivity from DMN to motor system is impaired in PD.