The case for combining tVNS and tSCS
Transcutaneous vagus nerve stimulation and transcutaneous spinal cord stimulation are often discussed independently, but they share a fundamental therapeutic philosophy: both represent a shift from compensatory to restorative rehabilitation. Rather than teaching patients to work around their deficits, these modalities aim to recover function by enhancing the nervous system's capacity for reorganisation.
The two approaches are complementary in their neuroanatomical targets. tVNS acts supraspinally, engaging brainstem nuclei (the locus coeruleus, raphe nuclei, and nucleus tractus solitarius) and modulating cortical excitability through norepinephrine and acetylcholine release. tSCS acts spinally, directly modulating spinal circuit excitability through posterior root afferent activation. Together, they address the full neuroaxis, from cortex to spinal cord.
A critical shared principle is that neither modality functions as standalone stimulation. Both require pairing with active, task-specific practice to produce meaningful functional gains. The stimulation creates conditions favourable for learning; the training provides the content of that learning. This positions both as rehabilitation enhancers rather than passive treatments.
Ten shared principles
When examined side by side, tVNS and tSCS share ten fundamental principles that inform clinical implementation.
1. Timing-dependent paired rehabilitation. Both modalities require temporal synchronisation with task practice. tVNS paired during movement attempts strengthens cortical motor representations; tSCS delivered concurrently with voluntary motor efforts enables activity-dependent strengthening of spinal synaptic connections. Standalone stimulation without training yields minimal functional benefit.
2. Session duration convergence. Despite targeting different neural levels, both modalities have independently converged on 30 to 60 minute stimulation sessions. The standard clinical architecture for both involves stimulation concurrent with task practice, followed by continued training during the carryover window. Both fit within standard 1 to 2 hour therapy blocks common in NHS and private rehabilitation settings.
3. Dose-response characteristics. The dose-response profiles differ in an important way. tVNS follows an inverted-U curve: moderate intensity is optimal, and increasing stimulation beyond a certain point may actually reduce benefit. tSCS follows a more linear pattern: more sessions generally produce greater benefit, with a minimum threshold of 60 sessions for sustained gains in chronic SCI. These distinct profiles have practical implications for parameter titration and for managing non-responders.
4. Multi-tiered carryover effects. Both produce temporally layered persistence of therapeutic benefit. Immediate effects last hours (2-hour motor carryover for tSCS, several hours for tVNS cognitive effects). Extended effects persist for days to weeks after multi-session protocols. Long-term structural neuroplastic changes can persist for months, supported by evidence from both clinical case reports and animal models.
5. Neuromodulation as plasticity primer. Perhaps the most conceptually important parallel: both modalities function as "gates" for plasticity rather than direct functional effectors. tVNS opens a cortical plasticity window through neuromodulatory nuclei activation. tSCS opens a spinal plasticity window by modulating interneuron excitability. In both cases, the enhanced neural environment must be filled with task-relevant practice to drive reorganisation.
6. Electrode placement criticality. Both require precise electrode positioning for optimal therapeutic outcomes. For tVNS, the cymba concha (with 100% vagal innervation) is preferred over the tragus (approximately 45% vagal innervation). For tSCS, cathodal electrode placement at the target spinal level (C3-C7 for upper extremity, T11-L2 for lower extremity) directly determines which circuits are modulated. In both cases, small differences in positioning can meaningfully affect outcomes.
7. Complementary autonomic modulation. Both modalities influence autonomic nervous system function. tVNS engages the cholinergic anti-inflammatory pathway and modulates sympathovagal balance. tSCS has demonstrated improvements in cardiovascular autonomic function in cervical SCI. For patients with autonomic dysregulation, which is common after spinal cord injury, the combination may offer benefits beyond motor function alone.
8. Shared safety profiles. Both are non-invasive, reversible, and associated with minimal adverse events. Common side effects for both are mild and local: skin irritation at electrode sites, tingling, and transient discomfort during initial parameter titration. Neither carries the surgical risks associated with implanted neuromodulation devices. This favourable safety profile supports application across diverse patient populations.
9. Compatible with existing rehabilitation workflows. Both modalities integrate into standard therapy sessions without requiring fundamental restructuring of clinical schedules. The 30-minute stimulation plus continued training model fits within existing appointment blocks. Both can be delivered by trained therapists using portable, user-friendly devices. Both support transition from clinic-based to home-based delivery after initial in-clinic training.
10. Emerging evidence for combined use. The theoretical rationale for combining tVNS and tSCS is strong: simultaneous cortical and spinal priming should enhance activity-dependent plasticity across the full motor pathway. Some patient populations may particularly benefit from dual-level neuromodulation, such as stroke patients with secondary spasticity (tVNS for cortical motor recovery, tSCS for spinal spasticity management) or SCI patients with cognitive fatigue (tSCS for motor function, tVNS for arousal and attention). Formal trials of combined protocols are in early stages.
A restorative philosophy
Both tVNS and tSCS reflect a shift in rehabilitation thinking that has been building over recent decades. Traditional approaches to chronic neurological conditions have focused primarily on compensation: teaching patients to use assistive devices, modify their environment, and employ alternative movement strategies. While these approaches remain valuable, they accept permanent loss of original function.
Neuromodulation-enhanced rehabilitation targets the underlying neural circuits to restore capacity. The VNS-REHAB trial demonstrated clinically meaningful motor recovery in stroke survivors averaging 2 years post-injury, well beyond the window traditionally considered amenable to recovery. tSCS trials have shown neurological level improvements in chronic spinal cord injury, with individuals regaining function that was thought permanently lost.
These are not isolated findings. They reflect a growing understanding that the nervous system retains significant capacity for reorganisation throughout the chronic phase of injury, and that appropriate neuromodulation paired with intensive training can access that capacity.
Anatomical Concepts has spent over 30 years pioneering rehabilitation technology, from functional electrical stimulation for denervated muscle to the current generation of neuromodulation devices. tVNS and tSCS represent the latest chapter in an evidence-based, clinician-guided, patient-centred approach to neurological rehabilitation. The underlying commitment remains the same: using technology to help patients recover function, guided by the best available evidence and delivered by skilled clinicians.
Future directions
The evidence base for both tVNS and tSCS is growing rapidly, and several developments will shape the field over the coming years.
The TRICEPS trial, running across 15 UK stroke centres, will provide real-world evidence for tVNS-enhanced upper limb rehabilitation in an NHS setting. Results are expected in July 2026, and a positive outcome would significantly strengthen the case for routine clinical adoption of tVNS in stroke rehabilitation.
Parameter standardisation remains a priority. Both modalities involve multidimensional parameter spaces (frequency, amplitude, pulse width, session duration, electrode placement), and the field would benefit from consensus protocols that enable more meaningful comparison across studies and centres.
Biomarker development for treatment response prediction is an active area of investigation. Currently, neither modality has validated biomarkers for prospectively identifying which patients are most likely to respond. Pupil dilation as an index of locus coeruleus activation shows promise for tVNS, and H-reflex modulation may serve a similar role for tSCS, but neither has been validated for clinical decision-making.
The development of formal combined tVNS and tSCS protocols, targeting both cortical and spinal plasticity simultaneously, represents a logical next step. Early-stage work is exploring optimal sequencing, parameter interactions, and patient selection criteria for dual-modality approaches.
The field is evolving rapidly. What is clear is that transcutaneous neuromodulation has moved from experimental curiosity to a credible adjunctive intervention in neurological rehabilitation, and the trajectory of evidence supports continued growth in both scope and clinical confidence.