TABLE 1.
Studies assessing cognitive effects of tVNS in young (A) and old (B) adults.
| A | ||||||||||||
| References | Design | N (Total) | N (Sham) | N (Stim) | Age—Sham | Age—Stim | Cognitive domain | Specific cognitive domain studied | Task | Outcome | Was a positive effect reported | Data collection method |
| Fischer et al., 2018 | Within-subject design | 21 | 21 | 21 | 20.3 | 20.3 | Executive functions | Conflict-triggered adjustment of cognitive control | ∙ Adapted response conflict Simon task ∙ Novelty Oddball task |
∙ tVNS reduced N2 and P3 amplitude after conflict ∙ Behaviorally, tVNS impacts conflict-related processing and less so in non-conflict trials. |
Yes | In-person |
| Jongkees et al., 2018 | Between-subject design | 40 | 20 | 20 | 22.3 | 22.5 | Executive functions | Action control performance | ∙ Serial reaction time task | ∙ tVNS enhances response selection processes when selection demands are particularly high | Yes | In-person |
| Colzato et al., 2018 | Between-subject design | 80 | 40 | 40 | 20.53 | 21.4 | Executive functions | Creativity | ∙ Divergent thinking task (Alternate Uses Task) ∙ Convergent thinking tasks (remote associates test, creative problem-solving task, idea selection task) |
∙ tVNS increased fluency scores (they were able to generate more answers in AUT task) ∙ tVNS increased cognitive flexibility scores (they were able to generate answers in more different categories in AUT task) ∙ No significant effect of tVNS on the three convergent thinking tasks (RAT, CPS and IST). |
Yes | In-person |
| Rufener et al., 2018 | Within-subject design | 20 | 20 | 20 | 24.85 | 24.85 | Executive functions | Auditory selective attention | ∙ Auditory oddball paradigm | ∙ tVNS increased P3 amplitude and reduced P3 latency ∙ tRNS reduced RT in oddball paradigm |
Yes | In-person |
| Pihlaja et al., 2020 | Within-subject design | 25 | 25 | 25 | 25.5 | 25.5 | Executive functions | Cognitive control-related neural processes | ∙ Executive reaction time test (RT-test) ∙ Go/no-go task |
∙ tVNS reduced frontal N2 in the NoGo condition ∙ No difference in behavior |
Yes | In-person |
| Borges et al., 2020 | Within-subject design | 32 | 32 | 32 | 23.17 | 23.17 | Executive functions | Task switching | ∙ Flanker task ∙ Spatial Stroop task ∙ Number-letter task ∙ Dimensional change card sorting task (DCCS) |
∙ tVNS can increase cognitive flexibility in a set-shifting paradigm (DCCS) | Yes | In-person |
| Keute et al., 2020 | Within-subject design | 22 | 22 | 22 | 23.8 | 23.8 | Executive functions | Conflict adaptation and executive control of action | ∙ Cued go–no-go-change-task | ∙ tVNS enhanced accuracy in go/change response conflicts ∙ Frontal midline theta was enhanced under tVNS during go/stop conflicts |
Yes | In-person |
| Tona et al., 2020 | Within-subject design | 48 | 48 | 48 | 21.4 | 21.4 | Executive functions | Cognitive flexibility | ∙ Cognitive emotion regulation tasks–Classifying a digit as high/low (Task 1)–Classifying a digit as odd/even (Task 2) | ∙ Reported no behavioral changes, and participants showed typical switch costs | No | In-person |
| Chen et al., 2022 | Between-subject design | 28 | 14 | 14 | 23.4* | 23.4* | Executive functions | Action planning | ∙ Action planning paradigm | ∙ tVNS reduces the reaction time of difficult tasks ∙ tVNS decreased MRCP amplitude in difficult tasks |
Yes | In-person |
| Klaming et al., 2022 | Between-subject design | 30 | 15 | 15 | 30 | 25 | Executive functions | Visuospatial problem solving | ∙ Matrix Reasoning (MR) Task ∙ Forced-Choice Recognition Task |
∙ nVNS leads to higher accuracy on visuospatial reasoning and memory recognition tasks (enhanced attention) | Yes | In-person |
| Wang C. et al., 2022 | Between-subject design | 58 | 29 | 29 | 19.58 | 19.4 | Executive functions | Inhibitory control | ∙ Stop-Signal task ∙ Simple reaction task ∙ Go/no-go task ∙ Color-word Stroop task |
∙ tVNS improved performance on the stop signal and Go/no-go tasks | Yes | In-person |
| Villani et al., 2022 | Within-subject design | 50 | 50 | 50 | 22.74 | 22.74 | Executive functions | Cognitive processes related to the LC-NA system | ∙ Auditory oddball task | ∙ tVNS increased RT to targets ∙ tVNS was associated with smaller pupil dilation |
Yes | In-person |
| Konjusha et al., 2022 | Within-subject design | 45 | 45 | 45 | 23.57 | 23.57 | Executive functions | Response selection, conflict monitoring | ∙ Flanker task | ∙ tVNS compromised performance as a function of prior task exposure. ∙ tVNS led to decreased alpha band EEG activity in middle and superior prefrontal regions |
No. Negative | In-person |
| Burger et al., 2018 | Between-subject design | 85 | 43 | 42 | 21.02* | 21.02* | Social/ Emotional |
Extinction of conditioned fear | ∙ Fear conditioning and fear extinction paradigm | ∙ Found no indications that tVNS accelerated the extinction of conditioned fear | No | In-person |
| Sellaro et al., 2018 | Within-subject design | 24 | 24 | 24 | 20.71 | 20.71 | Social/ Emotional |
Emotion recognition | ∙ Facial and bodily emotion recognition tasks | ∙ tVNS enhanced emotion recognition for whole faces but not for bodies | Yes | In-person |
| Burger et al., 2019b | Between-subject design | 97 | 49 | 48 | 21.04* | 21.04* | Social/ Emotional |
Negative thought intrusion | ∙ Breathing focus task | ∙ tVNS condition were more likely to report negative thought intrusions immediately post-worry induction but became less likely to do so as the post-worry period went on. | Yes | In-person |
| Burger et al., 2019a | Between-subject design | 58 | 29 | 29 | 21.5 | 22.1 | Social/ Emotional |
Fear memory and generalization | ∙ Fear conditioning, fear generalization, and fear extinction paradigm | ∙ tVNS facilitated extinction of declarative but not physiological fear expression | Yes | In-person |
| Finisguerra et al., 2019 | Within-subject design | 24 | 24 | 24 | 24.54 | 24.54 | Social/ Emotional |
Spiritual self-representations | ∙ Religious, Spiritual and Self-esteem implicit association tests and questionnaires (IAT tasks) | ∙ tVNS affected implicit spiritual, but not religious or control self-representations | Yes | In-person |
| Verkuil and Burger, 2019 | Between-subject design | 94 | 49 | 45 | 20.79 | 21.19 | Social/ Emotional |
Attention to fearful faces in high worriers | ∙ Emotional exogenous cueing task | ∙ tVNS did not affect performance on the exogenous cueing task | No | In-person |
| Steenbergen et al., 2020 | Within-subject design | 94 | 94 | 94 | 22.3 | 22.3 | Social/ Emotional |
Self-control and impulsivity | ∙ Delay discounting task | ∙ tVNS increased discounting, but only for individuals reporting lower positive mood | Yes | In-person |
| Maraver et al., 2020 | Within-subject design | 43 | 43 | 43 | 20 | 20 | Social/ Emotional |
Social information processing | ∙ Rapid Serial Visual Presentation Task | ∙ Active tVNS enhanced conditional T2 accuracy for both neutral and emotional faces | Yes | In-person |
| Szeska et al., 2020 | Between-subject design | 80 | 40 | 40 | 22.75* | 22.75* | Social/ Emotional |
Fear extinction | ∙ Multiple-day single-cue fear conditioning and extinction paradigm | ∙ tVNS during extinction training facilitated formation, consolidation, and long-term recall of extinction memory | Yes | In-person |
| De Smet et al., 2021 | Between-subject design | 83 | 41 | 42 | 21.34 | 20.86 | Social/ Emotional |
Cognitive reappraisal of emotions | ∙ Cognitive emotion regulation task | ∙ tVNS leads to improved cognitive reappraisal and rated their response to emotion-eliciting pictures as less intense ∙ No physiological differences to emotional stimuli were reported |
Yes | In-person |
| Steenbergen et al., 2021 | Within-subject design | 73 | 73 | 73 | 20.53 | 20.53 | Social/ Emotional |
Emotion recognition | ∙ Emotion recognition tasks | ∙ Active tVNS enhanced the recognition of anger but reduced the ability to recognize sadness | Yes | In-person |
| Johnson and Steenbergen, 2022 | Within-subject design | 38 | 38 | 38 | 21.2 | 21.2 | Social/ Emotional |
Emotional bias | ∙ Emotional dot-probe task | ∙ tVNS reduces the emotional bias toward faces expressing sadness and happiness (decrease in emotional reactivity) | Yes | In-person |
| Kaan et al., 2021 | Between-subject design | 62 | 33 | 29 | 19.8 | 20.4 | Memory | Verbal order memory | ∙ Word order memory task | ∙ tVNS was associated with higher accuracy on the order memory task | Yes | In-person |
| Zhao et al., 2023 | Within-subject design | 67 | 67 | 67 | 21.26 | 21.26 | Memory | Working memory | ∙ Psychomotor vigilance task (PVT) ∙ N-back tasks |
∙ tVNS improved participants accuracy rate in spatial 3-back task ∙ tVNS did not improve PVT performance |
Yes | In-person |
| Bretherton et al., 2019 | Within-subject design | 88 | 14 | 88 | 69.14 | 65.6 | Executive functions | Autonomic function, mood, and sleep | ∙ Quality of life (QoL), mood and sleep questionnaires | ∙ tVNS improved autonomic function and may improve some aspects of health related QoL, mood and sleep | Yes | In-person |
| Jackowska et al., 2022 | Between-subject design | 68 | 31 | 37 | 47.05 | 48.91 | Executive functions | Sleep | ∙ Pittsburgh Sleep Quality Index (PSQI) | ∙ tVNS there were significant improvements in global sleep scores over time | No | Remote |
| Wang L. et al., 2022 | Between-subject design | 52 | 27 | 25 | 67 | 66.9 | Executive functions | Cognitive function in patients with MCI | ∙ Montreal cognitive assessment-basic (MOCA-B) ∙ Auditory verbal learning test (AVLT-H) ∙ Shape trails test A&B (STT-A&B) ∙ AFT, BNT, PSQI, RBDSQ, ESS, FAQ |
∙ tVNS increases MoCA-B scores ∙ N5 and N7 in AVLT-H were increased in tVNS condition to various degrees |
Yes | Remote |
| Oehrn et al., 2022 | Within-subject design | 19 | 19 | 19 | 45 | 45 | Social/ Emotional |
Cooperative behavior in patients with epilepsy | ∙ Prisoner’s Dilemma Task | ∙ tVNS induces a behavioral starting bias toward cooperation | Yes | In-person |
| Mertens et al., 2020 | Within-subject design | 24 | 24 | 24 | 55.13 | 55.13 | Memory | Verbal memory | ∙ Word recognition memory paradigm | ∙ tVNS did not affect the accuracy scores for immediate recall or delayed recognition | No | In-person |
*Study did not state the difference in age means between the sham and stim groups.