What standardized rTMS protocols have been proposed for tinnitus and which parameters most influence outcomes?
Executive summary
Repetitive transcranial magnetic stimulation (rTMS) for chronic tinnitus has produced several repeatedly used protocols—most commonly low-frequency (1 Hz) stimulation to left temporoparietal/auditory cortex and sequential multilocus approaches that add prefrontal stimulation—but no single, universally accepted “standard” exists because trials report heterogeneous outcomes and methodological differences [1] [2] [3]. Key parameters that drive efficacy and explain variability are stimulation frequency and cortical target, pulse number and session count, intensity and coil configuration/orientation, and patient characteristics such as comorbid depression or tinnitus chronicity [3] [4] [5].
1. The most commonly proposed standardized protocols: low‑frequency auditory cortex and its sequels
The prototypical, repeatedly tested protocol is low‑frequency (1 Hz) rTMS applied over left temporoparietal or primary auditory cortex—rooted in the hypothesis that 1 Hz inhibits hyperactivity in auditory cortex—and this approach showed benefit in some controlled trials (e.g., Folmer et al.) but not in other large multicenter trials, illustrating inconsistent replication [1] [2] [6].
2. Sequential and multilocus protocols: pairing frontal and temporal targets
A strong body of work has tested sequential protocols that combine prefrontal (often DLPFC) and auditory cortex stimulation—either low‑frequency frontal stimulation (1 Hz) for short‑term benefit or high‑frequency frontal stimulation (20 Hz or 10 Hz) to attempt longer‑term gains—with pooled analyses and some trials reporting superiority of combined over single‑site stimulation in selected outcomes [7] [8] [9] [5].
3. Multisite, triple‑site and deep‑coil innovations under investigation
Researchers have tested triple‑site protocols (e.g., simultaneous/serial DLPFC 20 Hz plus bilateral temporoparietal 1 Hz) and combinations using deep H‑coils (H7) paired with conventional figure‑of‑eight coils; preliminary and pilot trials report tolerability and some promising response rates but remain insufficiently powered to define a new standard [9] [10] [5].
4. Personalization and test‑session strategies: a competing “standard” idea
Instead of a single protocol for all, personalization—using brief test stimulations to select the protocol that transiently reduces tinnitus loudness or that modulates biomarkers like auditory alpha—has been proposed and trialed; small studies indicate feasibility and possible secondary benefits, but randomized evidence so far has not shown clear superiority of personalized vs. standard protocols on primary outcomes [11] [6] [4].
5. Which technical parameters most influence outcomes: the mechanistic and practical levers
Frequency and cortical target are primary drivers—low‑frequency temporal protocols aim to suppress auditory hyperactivity, while high‑frequency prefrontal stimulation targets affective/attentional networks—yet effects are protocol‑ and patient‑dependent [6] [8]. Pulse number per session, total sessions, and timing (e.g., 10 sessions vs. 15) matter: some meta‑analyses and trials link more pulses/sessions to better responses, but findings are inconsistent [2] [1]. Intensity relative to resting motor threshold and coil type/orientation alter induced currents and thus outcomes, and many studies fail to report these details comprehensively—a key source of interstudy heterogeneity [3] [12]. Finally, patient factors—presence of major depressive disorder, tinnitus chronicity, hearing status, and inter‑individual neurophysiological differences such as baseline auditory alpha—moderate response probability [4] [5] [13].
6. Safety, tolerability and the limits of current “standardization”
Across large pooled analyses and randomized trials, rTMS for tinnitus has been repeatedly reported as generally well tolerated with no consistent serious adverse events, supporting broader testing—but the lack of standardized reporting on coil orientation, device brands, pulse counts, and outcome measures prevents declaration of a single evidence‑based standardized protocol [7] [9] [3].
7. Bottom line and the research agenda to reach a true standard
The literature points to a small set of leading protocols—left‑temporal 1 Hz, sequential DLPFC+temporal (various frequencies), and multisite combinations with emerging deep‑coil approaches—but heterogeneity in technical parameters and patient selection now explains conflicting trial results; resolving this requires large, multi‑site trials that standardize device/coiling/orientation, report intensity/pulse counts, stratify for comorbidities, and compare fixed vs. personalized strategies with long‑term outcomes [2] [3] [5].