Modulating Spinal Interoceptive Pathways to Evaluate Their Role and Therapeutic Potential in MDD Symptomatic Domains

Spinal interoceptive pathways (SIPs) convey bodily signals to an interoceptive system in the brain and their dysregulation is linked to major depressive disorder (MDD). Current treatments are partially effective and the role of SIPs in MDD is vastly unexplored. Preliminary data suggests that SIPs are feasible therapeutic targets in MDD. The central hypothesis is that non-invasive spinal cord stimulation will modulate SIPs to elucidate their role and therapeutic potential in MDD using an R61/33 phased innovation approach. R61 phase specific aims (SA). The specific goal will be to evaluate spinal and brain-based SIPs target engagement markers of transcutaneous spinal direct current stimulation (tsDCS) in MDD with two SAs: SA1) To determine tsDCS SIPs modulation using laser-evoked potentials (LEPs) as electroencephalography (EEG)- based neural measures of target engagement. SA2) To evaluate optimal tsDCS dose based upon tolerability and SIPs target engagement markers. Anodal tsDCS will be evaluated as a tool to modulate SIPs in MDD. SIPs (Aδ and C fibers) can be evaluated via LEPs as neural measures (EEG) elicited in MDD-relevant brain regions within an interoceptive system. Prior data shows anodal tsDCS inhibits SIPs and LEPs N2 component will be assessed as tsDCS engagement markers. Adults with MDD (n=67) will participate in a double-blind, crossover, sham-controlled study to evaluate tsDCS at 0,2.5,3, and 3.5 mA. The working hypothesis is that tsDCS will induce a change in LEPs (SA1) in a dose-dependent and tolerable manner (SA2), supporting their use as SIPs engagement markers. Go/No-Go milestones: Compared to sham, the active tsDCS dose that induces a change in LEPs at a preestablished threshold will be evidence of SIPs engagement and "Go" criteria for the R33 phase.