FND Education Project

REFERENCE · DIAGNOSTIC TECHNIQUE

Entrainment in Functional Tremor

Purpose and Suitability
Anatomy and Physiology
Preparation and Examination
Interpretation and Explanation
Evidence and Limitations
Media and Accessibility
Research and Sources

Purpose and Suitability

Entrainment means that an involuntary tremor takes on the rhythm of a deliberate movement made by another limb. The clinician compares the tremor with the rhythm the person actually produces, not simply with the metronome’s setting. A pause, irregularity or smaller movement is recorded separately. [1]

Metronome: A device or cue that marks a regular beat. Frequency: How many movement cycles occur in one second; measured in hertz (Hz).

The method described here concerns limb tremor, especially the hands. It is a diagnostic comparison for a trained clinician. Rehabilitation may use rhythm for a different purpose; that is covered in the recovery technique.

Purpose and Suitability
Anatomy and Physiology
Preparation and Examination
Interpretation and Explanation
Evidence and Limitations
Media and Accessibility
Research and Sources

Anatomy and Physiology

The hand’s movement reflects muscle contractions around its joints. Tapping the other hand introduces a second rhythm that can be compared with the ongoing tremor. In laboratory assessment, skin electrodes record muscle activity and movement sensors record motion in both limbs. [2]

Contralateral: On the opposite side. Coherence: A signal-analysis measure of how consistently two recordings share a rhythm.

The important question is whether the original tremor changes into the tapping rhythm. A movement transmitted through a shared surface, or an extra mirrored movement, may create a misleading appearance of matching rhythms. A case report demonstrates why the original tremor signal still matters. [4]

Mirror movement: An unintended movement on one side that accompanies a deliberate movement on the other.

This comparison does not locate a single damaged brain area or establish a psychological cause.

Purpose and Suitability
Anatomy and Physiology
Preparation and Examination
Interpretation and Explanation
Evidence and Limitations
Media and Accessibility
Research and Sources

Preparation and Examination

Explain the comparison, obtain consent and agree a stop signal. Check whether the less affected limb can carry out the task. Use a comfortable seated position with appropriate support; record any adaptation needed for pain, fatigue, weakness or sensory access.

  1. Observe the original tremor. Record its position, size and approximate rhythm before adding a tapping task.
  2. Explain and practise the tapping instruction. Ask the less affected hand to make small movements to a tolerable pacing cue. Small taps reduce mechanical transmission between limbs. [1]
  3. Compare at different rhythms. Observe both limbs while the tapping rate changes. The 2011 laboratory protocol used 1, 3 and 5 Hz with recordings under defined conditions. A comfortable bedside demonstration is not equivalent to completing that protocol. [2]
  4. Check the rhythm actually produced. If the person cannot follow the requested beat, record that. Do not call the tremor entrained to a rhythm the tapping limb never maintained.
  5. Separate the possible responses. Describe matching of the tremor to tapping, a frequency shift without matching, suppression, irregularity or no clear change. Return to baseline and repeat only enough for interpretation.
  6. Resolve uncertainty rather than forcing a result. When matching is uncertain or another tremor may coexist, a specialist may use surface EMG and movement recordings. Stop if the task becomes painful, exhausting or otherwise intolerable.

Keep the camera or recording position stable. Never steady a limb by force to produce a preferred response.

Purpose and Suitability
Anatomy and Physiology
Preparation and Examination
Interpretation and Explanation
Evidence and Limitations
Media and Accessibility
Research and Sources

Interpretation and Explanation

Matching at one rate close to the original tremor is difficult to interpret. Following more than one distinctly different tapping rhythm provides a clearer comparison. Suppression during tapping can be relevant to distractibility; it should not be relabelled as entrainment. [1][2]

Record uncertainty if the original tremor persists beneath an added rhythm. In the 2018 case report, recordings revealed a continuing tremor component alongside the apparent rhythm coupling. The authors considered mirror movement and functional overlap. That single case illustrates a pitfall rather than its frequency. [4]

A small later series described “mixed entrainment,” with both original and tapping-frequency peaks. It does not settle the differential or make every extra peak evidence of FND. [5]

An example explanation is: “When your other hand changed its tapping rhythm, the shaking followed it. That pattern helps explain why we think this tremor is functional. We still need to understand what it prevents you doing and whether another condition is present.”

A positive comparison does not establish reliable writing, eating or sustained hand use. Record assistance and everyday impact separately; see assessment and everyday function.

Purpose and Suitability
Anatomy and Physiology
Preparation and Examination
Interpretation and Explanation
Evidence and Limitations
Media and Accessibility
Research and Sources

Evidence and Limitations

Development study: In 2011, entrainment occurred in five of 13 functional tremors and none of 25 comparison tremors. The small selected cohort and older clinical reference criteria limit generalization. Most functional cases did not entrain, so absence is not an exclusion rule. [2]

Prospective validation: The 2016 study assessed a complete electrophysiological battery in a new cohort, with raters blinded to diagnosis. It supports the combined assessment; its accuracy estimates are not entrainment-only estimates. The distractibility evidence section reports the cohort and battery figures. [3]

Newer exploratory evidence: Murgai and Iskhakova retrospectively studied ten clinically diagnosed patients. Seven showed entrainment at one or more rates, with pure, mixed or both patterns. No non-functional comparison group was included, so specificity cannot be calculated. [5]

Specificity: How often a test is negative in people without the condition being assessed.

Current synthesis: The 2026 meta-analysis found heterogeneous results across electrophysiological tests and comparatively stronger performance for batteries. A pooled result across different tests is not the accuracy of this manoeuvre. [6]

Access and scope: Full texts were checked for the 2011 study, 2018 case report, newer ten-patient series and IFCN chapter. The 2016 validation and 2026 synthesis were available at abstract level only. Further full-text review remains pending. Most validation concerns limb tremors; coexisting tremor disorders and other body sites need particular caution.

Purpose and Suitability
Anatomy and Physiology
Preparation and Examination
Interpretation and Explanation
Evidence and Limitations
Media and Accessibility
Research and Sources

Media and Accessibility

Use one continuous medium-width shot that includes the tremulous limb, the tapping limb and the clinician’s instructions. Add a small on-screen rhythm label—such as “slow,” “medium” and “fast”—and preserve the original audio so viewers can match the tapping to any tremor change.

Show baseline, clearly explained tapping at different rates, and return to baseline before any replay. Keep the actual tapping visible so the requested beat is not confused with the performed movement. Obtain separate consent for recording and public use.

Do not use rapid cuts, speed changes or music over the examination. Those edits would make frequency comparison unreliable. Captions should describe the task rather than declare that the sign “proves FND.”

Provide a transcript describing each condition and what changed. Keep pacing sound comfortable and optional for viewers; a video should not need flashing cues. The earlier combined media brief is preserved here in scope, with no new illustration presented as clinically approved.

Purpose and Suitability
Anatomy and Physiology
Preparation and Examination
Interpretation and Explanation
Evidence and Limitations
Media and Accessibility
Research and Sources

Research and Sources

The primary development and validation studies concern laboratory procedures. The mirror-movement report and newer small series identify interpretation questions; neither resolves all mixed tremor presentations. The example explanation is editorial wording, not a patient quotation.

Citation Figure Full citation
[1] — Edwards MJ, Koens LH, Liepert J, Nonnekes J, Schwingenschuh P, van de Stouwe AMM, Morgante F. Clinical neurophysiology of functional motor disorders: IFCN Handbook Chapter. Clinical Neurophysiology Practice. 2024;9:69–77. https://doi.org/10.1016/j.cnp.2023.12.006 FND-CIT-0022.
[2] — Schwingenschuh P, Katschnig P, Seiler S, et al. Moving toward “laboratory-supported” criteria for psychogenic tremor. Movement disorders : official journal of the Movement Disorder Society. 2011;26(14):2509-2515. DOI. PMID: 21956485. FND-CIT-0177.
[3] — Schwingenschuh P, Saifee TA, Katschnig-Winter P, et al. Validation of “laboratory-supported” criteria for functional (psychogenic) tremor. Movement disorders : official journal of the Movement Disorder Society. 2016;31(4):555-562. DOI. PMID: 26879346. FND-CIT-0178.
[4] — Merchant SH, Haubenberger D, Hallett M. Mirror movements or functional tremor masking organic tremor. Clinical neurophysiology practice. 2018;3:107-113. DOI. PMID: 30215019. FND-CIT-0154.
[5] — Murgai A, Iskhakova S. Entrainment characteristics of functional tremor. Movement Disorders Clinical Practice. 2025;12(2):253–254. Published online November 4, 2024. DOI. Full text. FND-CIT-0222.
[6] — Rujirussawarawong S, Ounmuang C, Aungsumart S, Kasemsuk C, Limotai N. Electrophysiology in distinguishing functional tremor from organic tremor: a systematic review and meta-analysis of diagnostic accuracy. Movement Disorders Clinical Practice. Published online June 11, 2026. DOI. PubMed. FND-CIT-0224.

Purpose and Suitability
Anatomy and Physiology
Preparation and Examination
Interpretation and Explanation
Evidence and Limitations
Media and Accessibility
Research and Sources