Neurostimulation & neurofeedback · graded by use, four uses
Transcutaneous Vagus Nerve Stimulation
Postoperative cognitive dysfunction in older adults having major surgery.
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How this letter has changedLatest: October 2026 · Upgraded.
The perioperative use was held at B because the Montreal Cognitive Assessment is administered rather than recorded by an instrument. The written A definition also accepts a validated outcome scale scored by a clinician blinded to treatment, and two double-blind Neither the participants nor the people assessing them know who received the real treatment until the trial ends. trials from independent groups found less postoperative cognitive dysfunction with active stimulation: Zhou et al. (Aging Clin Exp Res, 2022; PMID PubMed ID: the permanent number the US National Library of Medicine gives a published paper. Each one links to that paper's record on PubMed. 35809206) and Ma et al. (J Geriatr Oncol, 2026; PMID 42456197), with Li et al. (Neuromodulation, 2026; PMID 42104979) agreeing. The use moves to A, with the limits (one country, about 100 patients per trial, one retrospective registration) stated beside the letter. Applied the written grade definition at the editor's request of October 2026 to settle the calls the definitions decide (Arnold Sandlow, D.C.).PMID 35809206 PMID 42104979 PMID 42456197
The record graded a whole modality on one cognition meta-analysis A study that pools the numbers from several trials into one combined estimate. with no population, device or dose, and named an autonomic endpoint The outcome a trial measures to decide whether the treatment worked, such as heart attacks, blood pressure or a symptom score. with no autonomic citation. It now carries four uses. Postoperative cognitive dysfunction in older surgical patients: three double-blind sham-controlled trials from three centers agree (Zhou et al., 2022; PMID 35809206; Li et al., 2026; PMID 42104979; Ma et al., 2026; PMID 42456197), with less postoperative delirium in a fourth (Shi et al., 2026; PMID 41835922); a validated cognitive test replicated The same finding reproduced by a separate research group. A result seen once can be chance or bias; a replicated one is harder to explain away. across independent groups meets the written B definition, and the headline follows the best use, C to B. Cognitive test performance in mixed samples stays C on the heterogeneous pools (Liu et al., 2026; PMID 42339645; Ridgewell et al., 2021; PMID 34043386). Mild cognitive impairment is C on one trial (Wang et al., 2022; PMID 36150665). Heart rate variability in healthy adults is D on Route 2 Human randomized trials have been run and did not show benefit on the stated outcome. One of the two routes to the lowest letter on EBL's scale., tested and no benefit shown in pooled sham-controlled trials (Souza et al., 2026; PMID 41506123; Soltani et al., 2023; PMID 37119426). Applied the written grade definition under the editor's standing instruction of October 2026 (Arnold Sandlow, D.C.).PMID 34043386 PMID 35809206 PMID 36150665 PMID 37119426 PMID 41506123 PMID 41835922 PMID 42104979 PMID 42339645 PMID 42456197
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This device sends a mild electrical current through the skin of the outer ear to reach the vagus nerve. Three trials in older adults having major surgery found less decline in memory and thinking after surgery than with a fake treatment. Testers did not know who got the real device. All three trials were small and from one country. Results for thinking in healthy adults and in mild memory problems are less certain. Pooled trials found no effect on heart rate variability.
The A belongs to one of the four uses graded on this record. The other three carry their own letters.
As studied, and the trials
Three sham-controlled trials agree: Zhou et al. (2022; PMID 35809206) and Ma et al. (2026; PMID 42456197), both double-blind, and Li et al. (2026; PMID 42104979), with Shi et al. (2026; PMID 41835922) finding less postoperative delirium in 150 patients as a related endpoint. A validated cognitive scale scored without knowledge of allocation, replicated across independent groups, meets the written A definition. Limits stated beside the letter: all three trials are from one country and about 100 patients each, and one was registered retrospectively.
As studied, and the trials
Liu et al. (2026; PMID 42339645) pool 30 studies: g 0.41 overall, strongest for executive function, with no difference between clinical and healthy samples. Ridgewell et al. (2021; PMID 34043386) pool 19 studies in healthy adults: g 0.21. The studies are small, mostly single laboratory sessions, and differ in device, site, intensity and population, so no specific protocol has two independent positive trials: C.
As studied, and the trials
Wang et al. (2022; PMID 36150665): double-blind trial, MoCA-Basic improved at 24 weeks against an acupoint-site sham. One trial, not repeated: C.
As studied, and the trials
Souza et al. (2026; PMID 41506123) pooled the sham-controlled trials and found no significant effect of transcutaneous vagus stimulation on heart rate variability; Soltani et al. (2023; PMID 37119426) found mixed results across 21 studies in healthy people, with baroreflex sensitivity changed in 1 of 6. Tested, no benefit shown: D on Route 2.
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See the full evidence record →Graded on Postoperative cognitive dysfunction in older adults having major surgery, on the Montreal Cognitive Assessment.
Why this gradeThe reasoning, and what the grade does not cover.
Grade A on postoperative cognitive dysfunction in older surgical patients. Three double-blind sham-controlled trials from three Chinese centers found less cognitive dysfunction on the Montreal Cognitive Assessment with auricular stimulation around surgery: Zhou et al. (2022; PMID 35809206), 124 patients, 10 against 27 percent; Li et al. (2026; PMID 42104979), 103 patients, 10 against 33 percent; Ma et al. (2026; PMID 42456197), 103 patients, MoCA 2 to 3 points higher through 3 months. A validated cognitive scale scored blind to allocation, replicated across independent groups, meets the written A definition. The limits are stated beside the letter: the trials are small, all from one country, and one was registered retrospectively.
WHAT THIS GRADE DOES NOT COVERcognition in healthy adults or mixed samples, Grade C, where pooled effects (Liu et al., 2026; PMID 42339645; Ridgewell et al., 2021; PMID 34043386) come from small, mostly single-session laboratory studies of different devices and sites; mild cognitive impairment, Grade C on one trial (Wang et al., 2022; PMID 36150665); heart rate variability in healthy adults, Grade D, tested and no benefit shown in pooled sham-controlled trials (Souza et al., 2026; PMID 41506123); mood, inflammatory or pain claims; implanted vagus nerve stimulation; and any specific consumer device, none of which was used in these trials.
Shared endpoint: Postoperative cognitive dysfunction or delayed neurocognitive recovery on the Montreal Cognitive Assessment or a neuropsychological battery, assessed blind to allocation, active against sham auricular stimulation
- Zhou 2022, joint replacement, China: delayed neurocognitive recovery 10 percent against 27 percent at 1 week, 124 patients. PMID 35809206 · Funding: National Natural Science Foundation of China
- Li 2026, gastrointestinal tumor surgery, China: postoperative cognitive dysfunction 10.2 percent against 32.7 percent, 103 patients. PMID 42104979 · Funding: not stated in the indexed record; registered retrospectively
- Ma 2026, laparoscopic gastrointestinal tumor resection, China: MoCA 2.1 to 3.0 points higher than sham at 1 and 3 months, 103 patients. PMID 42456197 · Funding: not stated in the indexed record
What the replication does not cover: All three trials are from China and enroll about 100 to 125 patients; one was registered retrospectively and two do not state their funder; no trial reports function or independence after discharge.
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Each use, with its trials
This record carries a separate letter for each thing it has been measured on. The headline grade is the best of them, and it does not transfer to the others.
Three sham-controlled trials agree: Zhou et al. (2022; PMID 35809206) and Ma et al. (2026; PMID 42456197), both double-blind, and Li et al. (2026; PMID 42104979), with Shi et al. (2026; PMID 41835922) finding less postoperative delirium in 150 patients as a related endpoint. A validated cognitive scale scored without knowledge of allocation, replicated across independent groups, meets the written A definition. Limits stated beside the letter: all three trials are from one country and about 100 patients each, and one was registered retrospectively.
Liu et al. (2026; PMID 42339645) pool 30 studies: g 0.41 overall, strongest for executive function, with no difference between clinical and healthy samples. Ridgewell et al. (2021; PMID 34043386) pool 19 studies in healthy adults: g 0.21. The studies are small, mostly single laboratory sessions, and differ in device, site, intensity and population, so no specific protocol has two independent positive trials: C.
Wang et al. (2022; PMID 36150665): double-blind trial, MoCA-Basic improved at 24 weeks against an acupoint-site sham. One trial, not repeated: C.
Souza et al. (2026; PMID 41506123) pooled the sham-controlled trials and found no significant effect of transcutaneous vagus stimulation on heart rate variability; Soltani et al. (2023; PMID 37119426) found mixed results across 21 studies in healthy people, with baroreflex sensitivity changed in 1 of 6. Tested, no benefit shown: D on Route 2.
The evidence, in fullNine papers, each linked to its PubMed record.
Perioperative cognition, three sham-controlled trials from three Chinese centers: Zhou et al. (Aging Clin Exp Res, 2022; PMID 35809206), 124 older adults having joint replacement, auricular stimulation from 1 hour before anesthesia to the end of surgery; delayed neurocognitive recovery at 1 week in 10 percent against 27 percent with sham, with lower IL-6 and S100-beta; funded by the National Natural Science Foundation of China. Li et al. (Neuromodulation, 2026; PMID 42104979), 103 older patients having gastrointestinal tumor surgery, 30 minutes daily from the day before to day 4 after; postoperative cognitive dysfunction on the MoCA in 10.2 percent against 32.7 percent; registered retrospectively. Ma et al. (J Geriatr Oncol, 2026; PMID 42456197), 103 older adults after laparoscopic gastrointestinal tumor resection, double-blind; MoCA higher from day 7 through 3 months, by 2 to 3 points. Shi et al. (Clin Interv Aging, 2026; PMID 41835922): 150 patients aged 65 and over, stimulation during major non-cardiac surgery; postoperative delirium 12 against 25 percent, a related endpoint. Cognition in mixed samples: Liu et al. (Psychol Med, 2026; PMID 42339645), systematic review A review that searches for every study on a question using a method set in advance, then assesses them together. of 53 studies with 30 pooled, more than 1,500 participants; g 0.41 overall, strongest for executive function, across healthy and clinical samples, mostly short laboratory tasks with varied devices and sites. Ridgewell et al. (Neuropsychology, 2021; PMID 34043386): 19 studies in healthy adults, g 0.21, mainly executive function. Wang et al. (Brain Stimul, 2022; PMID 36150665): 52 patients with mild cognitive impairment, double-blind, acupoint-site sham; MoCA-Basic improved at 24 weeks, one trial. Autonomic: Souza et al. (Auton Neurosci, 2026; PMID 41506123), meta-analysis of 13 sham-controlled trials of which 6 used transcutaneous vagus stimulation; no significant effect on time- or frequency-domain heart rate variability. Soltani et al. (Clin Auton Res, 2023; PMID 37119426): systematic review of 21 studies in healthy people; results mixed, baroreflex sensitivity changed in 1 of 6 studies. Grade A on the perioperative use: a validated cognitive scale scored blind, replicated across three independent sham-controlled trials, none large and all from one country.
The endpoint of the graded use: the Montreal Cognitive Assessment before and after surgery for the perioperative use; a cognitive test battery for cognition; resting heart rate variability only as a research measure, since pooled trials found no effect. Stimulation parameters (frequency, pulse width, current, site) at every session: auricular and cervical stimulation have different evidence and are not interchangeable.
Evidence notes: randomized trial, meta-analysis
Endpoint graded: Postoperative cognitive dysfunction in older adults having major surgery, on the Montreal Cognitive Assessment (clinician_rated)
Last reviewed: July 2026
Educational use only · Not medical advice · EBL grades published human evidence and does not recommend treatment. Stopping a prescription is a decision for your physician.
Primary evidenceNine papers, each linked to its PubMed record.
Perioperative cognition, three sham-controlled trials from three Chinese centers: Zhou et al. (Aging Clin Exp Res, 2022; PMID 35809206), 124 older adults having joint replacement, auricular stimulation from 1 hour before anesthesia to the end of surgery; delayed neurocognitive recovery at 1 week in 10 percent against 27 percent with sham, with lower IL-6 and S100-beta; funded by the National Natural Science Foundation of China. Li et al. (Neuromodulation, 2026; PMID 42104979), 103 older patients having gastrointestinal tumor surgery, 30 minutes daily from the day before to day 4 after; postoperative cognitive dysfunction on the MoCA in 10.2 percent against 32.7 percent; registered retrospectively. Ma et al. (J Geriatr Oncol, 2026; PMID 42456197), 103 older adults after laparoscopic gastrointestinal tumor resection, double-blind; MoCA higher from day 7 through 3 months, by 2 to 3 points. Shi et al. (Clin Interv Aging, 2026; PMID 41835922): 150 patients aged 65 and over, stimulation during major non-cardiac surgery; postoperative delirium 12 against 25 percent, a related endpoint. Cognition in mixed samples: Liu et al. (Psychol Med, 2026; PMID 42339645), systematic review of 53 studies with 30 pooled, more than 1,500 participants; g 0.41 overall, strongest for executive function, across healthy and clinical samples, mostly short laboratory tasks with varied devices and sites. Ridgewell et al. (Neuropsychology, 2021; PMID 34043386): 19 studies in healthy adults, g 0.21, mainly executive function. Wang et al. (Brain Stimul, 2022; PMID 36150665): 52 patients with mild cognitive impairment, double-blind, acupoint-site sham; MoCA-Basic improved at 24 weeks, one trial. Autonomic: Souza et al. (Auton Neurosci, 2026; PMID 41506123), meta-analysis of 13 sham-controlled trials of which 6 used transcutaneous vagus stimulation; no significant effect on time- or frequency-domain heart rate variability. Soltani et al. (Clin Auton Res, 2023; PMID 37119426): systematic review of 21 studies in healthy people; results mixed, baroreflex sensitivity changed in 1 of 6 studies. Grade A on the perioperative use: a validated cognitive scale scored blind, replicated across three independent sham-controlled trials, none large and all from one country.
Products carry no letter. The letter belongs to the therapy as the trials studied it, and no trial tested these products unless the entry says so. Listed alphabetically; payment does not affect order.
FDA-cleared for migraine and cluster headache, the strongest regulatory approval among consumer VNS devices. Cervical application. Prescription required in the US.
Auricular (ear-based) transcutaneous VNS. The strongest evidence base for non-invasive VNS, auricular stimulation targets the vagal auricular branch directly. CE-marked medical device.
Non-invasive neck-based VNS. HRV improvement and stress reduction data from company-sponsored studies. Consistent user-reported outcomes. Growing independent evidence base.
Handheld non-invasive cervical vagus nerve stimulator, sold as a general wellness product in two models, Truvaga 350 and Truvaga Plus. No trial has tested this device.
Handheld device applied to the side of the neck (cervical). The graded evidence for this modality is mostly auricular stimulation at the ear, a different site; the company’s own data is an internal 34-person survey, not a trial.
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(transcutaneous[tiab] OR auricular[tiab]) AND "vagus nerve stimulation"[tiab] AND (cognit*[tiab] OR "heart rate variability"[tiab]) AND (randomized controlled trial[pt] OR meta-analysis[pt]) AND humans[mesh]Grades move when new trials publish. A free monthly email lists every grade EBL moved, with the reason and the trial behind it: the sign-up is on the Evidence Log →