Biology subjects

Del Brocco, M.

Publications and source records attributed to Del Brocco, M..

3 recordsLinked to original sources

bioRxiv2026

Functional Somatotopy of Lumbar Dorsal Rootlets and its Role in Selective Recruitment via Lateral Spinal Cord Stimulation

ObjectiveLateral spinal cord stimulation (LSCS) is a promising approach for restoring somatosensory feedback in lower-limb amputees, but its spatial selectivity remains limited. Percepts often spread to unintended regions of the residual limb, and reducing electrode contact size may not improve focality. This study investigated whether the anatomical organization of lumbar dorsal rootlets (DR) imposes fundamental constraints on LSCS selectivity. ApproachAcute neurophysiology experiments were performed in six adult cats. Both LSCS and individual DR stimulation were conducted in the same animals. For DR stimulation, bipolar hook electrodes were used to stimulate individual DR, while antidromic compound action potentials (CAPs) were recorded from femoral and sciatic nerve branches instrumented with nerve cuffs. For LSCS, custom 32-contact epidural paddle electrodes were placed over the lateral surface of the spinal cord at corresponding vertebral levels. Recruitment thresholds, dynamic ranges, and response patterns were analyzed across spinal levels, and DR recruitment patterns were directly compared to those evoked by LSCS within the same animals. Main resultsA clear rostrocaudal organization was observed across spinal levels during stimulation of individual DR, with femoral branches predominantly recruited at L4-L5 and sciatic branches at L6-L7. However, no somatotopic organization was found across DR within each spinal level; individual DR frequently co-activated multiple branches within the same group, and selective recruitment could only be maintained over a narrow dynamic range (median [~]10 {micro}A). LSCS exhibited even a narrower dynamic range ([~]5 {micro}A) but closely mirrored DR recruitment patterns, indicating that LSCS activates sensory afferents in a manner determined by the organizational structure of the DR. SignificanceThese findings demonstrate that the limited spatial selectivity of LSCS can largely be attributed to the coarse organization of DR within each root level rather than due to limitations of epidural electrode design. Moving electrodes intradurally or reducing contact size further is unlikely to substantially improve focality. Instead, improving paddle stability to ensure consistent placement over the appropriate spinal levels may be a more effective strategy for enhancing percept localization.

neuroscience↗

bioRxiv2026

Selectivity of Lateral Epidural Spinal Cord Stimulation with Varying Electrode Diameters and Stimulation Configurations

Objective. Our prior studies have demonstrated that lateral spinal cord stimulation can evoke somatosensory percepts in the missing foot in individuals with a lower-limb amputation. However, subjects reported concurrent sensations in their residual limb. In this study, we evaluate the hypothesis that using high-density paddle electrodes with smaller contact sizes, and multipolar stimulation configurations could evoke more focal sensations in the foot over a wide range of stimulation amplitudes. Approach. We used a combination of electrophysiology and computational modelling methods to investigate the selective activation of distal nerve branches in response to lateral spinal cord stimulation in cats. In six acute feline experiments, we performed an L3-S1 laminectomy and placed custom 32-electrode paddles laterally over the dura of the spinal cord. We recorded antidromic action potentials in the distal branches of the sciatic and femoral nerve trunks in response to stimulation using three contact diameters (150, 500 and 1000 {micro}m) and two stimulation configurations - monopolar and bipolar stimulation. We replicated the neural recruitment patterns from those experiments in a computational model of the feline lumbar spinal cord. We then used the model to examine neural recruitment with 1.8 mm and 2.5 mm contacts, as well as a tripolar guarded-cathode configuration. Main results. In the electrophysiology experiments, the 500 {micro}m-diameter electrodes achieved the most selective nerve activation (68%) compared to 62% for both 150 and 1000 {micro}m-diameter electrodes. The minimum amplitudes for recruiting nerve branches (i.e., threshold) as well as the dynamic ranges were largely similar for the different contact diameters (median: 35 {micro}A) and stimulation configurations (30 {micro}A for bipolar stimulation; 35 {micro}A for monopolar stimulation). The computational model reproduced the finding that selectivity did not differ significantly among the three contact sizes tested in cat experiments, though it revealed that increasing contact diameter above 1000 {micro}m raised the minimum amplitude required for selective activation and reduced spinal root selectivity. Across both approaches, we consistently recruited large-diameter afferents that are critical for somatosensory applications of spinal cord stimulation. Significance. Our results indicate that, relative to clinical electrodes, reducing the contact diameter of stimulation electrodes can evoke focal sensations, but further reductions below 1000 {micro}m may fail to improve selectivity. This study highlights potential constraints with achieving focal selectivity that are not dependent on the design of the electrodes.

bioengineering↗

bioRxiv2025

SpIC3D imaging: Spinal In-situ Contrast 3D imaging

High-definition visualization techniques are critical for understanding the neuroanatomy of the spinal cord, an essential structure for sensorimotor and autonomic functions, in both healthy and pathological conditions. Magnetic resonance imaging (MRI) is a common method for visualizing neural structures in 3D. However, techniques for spinal cord MRI have historically achieved limited visualization of rootlets and nerves, especially at lower spinal levels, due to their highly complex and compact organization. Here we developed a spinal in-situ contrast 3D imaging (SpIC3D) method that allows visualization of spinal compartments in fixed animal and human specimens with ultra-high resolution at various spinal levels. Using SpIC3D, we achieved quantification of neuronal cell density in dorsal root ganglia, multi-segment identification of individual rootlets and roots, and volumetric reconstruction of multiple spinal structures for computational modeling. SpIC3D provides a basis for accelerated spinal pathology characterization and personalized spinal cord stimulation treatments.

neuroscience↗