Test Protocols

Adaptation Test (ADT)

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In this module

  1. Overview of the ADTFoundation · Trainee · Clinician
  2. Toes-up and toes-down rotationsFoundation · Trainee · Clinician
  3. Sway energyTrainee · Clinician
  4. Central adaptationFoundation · Trainee · Clinician
  5. Pattern interpretationTrainee · Clinician

Overview of the ADT

The Adaptation Test measures the central nervous system's ability to learn from a perturbation and damp the response across trials. It is the CDP protocol most sensitive to cerebellar involvement.

The test consists of two series of five trials each: toes-up rotations of the platform, and toes-down rotations. Each rotation lifts or drops the front of the platform by about 8 degrees over 400 ms.

The response to a toes-up rotation is initially exaggerated — the patient sways backward as if pushed. By the fifth trial, the healthy central nervous system has learned that the perturbation is harmless and damps the response. Sway energy on trial five is typically 40–60% of trial one.

Toes-up and toes-down rotations

Toes-up rotation: the front of the platform rises. The patient's body initially leans forward (relative to the new platform tilt), then sways backward as a corrective response. Healthy adults overshoot slightly on trial one, then progressively adapt.

Toes-down rotation: the front of the platform drops. The patient leans backward, then sways forward correctively. The adaptation pattern is similar to toes-up, although mean sway energies are typically a touch lower.

Some clinicians report toes-up and toes-down separately because asymmetric adaptation can occur — typically with toes-down adapting faster than toes-up. The interpretation of mild asymmetry is not standardised; treat it as a soft finding unless one direction is clearly non-adapting.

Sway energy

Sway energy is the integrated sway across the trial, weighted by frequency. It captures both the amplitude and the timing of the postural response in a single number. Higher values mean more total sway; the system normalises to a baseline so that direct trial-to-trial comparison is meaningful.

On a healthy first trial, sway energy is high — the patient hasn't yet learned the perturbation. By trial five, sway energy has typically dropped substantially: a fall of 40–60% from trial one is normal.

A flat trajectory across all five trials — sway energy on trial five roughly equal to trial one — is the abnormal finding. It means the central adaptation machinery is not learning. Cerebellar disease is the most specific cause; some central white-matter disorders can produce similar patterns.

Central adaptation

Adaptation requires cerebellar circuitry, particularly the anterior vermis and the interposed nuclei. These regions receive input about the perturbation (from somatosensory afferents and the vestibular system) and tune the descending motor command on subsequent trials.

The time-course of adaptation is rapid: most of the gain occurs between trials one and three. A patient who reaches their floor sway energy by trial three and stays flat for trials four and five is adapting normally; a patient whose trial-five sway is essentially identical to trial one is not.

Adaptation is reversible in the short term — fully-adapted patients tested again after a half-hour rest will show a partial return of trial-one responses, though usually not the full pre-adaptation level. Day-to-day learning probably accumulates more slowly via the same circuitry.

Pattern interpretation

Three patterns matter. Normal adaptation: clear downward trend across the five trials in both directions; trial five well below trial one. Most patients fall here.

Failure of adaptation: flat or even upward trend. Strongly suggestive of cerebellar disease, especially if accompanied by clinical signs (dysmetria, ataxia, gaze-evoked nystagmus). Demyelinating disease, late-stage Parkinson's, and some metabolic encephalopathies can also produce non-adapting ADT.

Direction asymmetry: adaptation in one direction but not the other. The interpretation here is uncertain; mild asymmetry probably reflects normal inter-trial variability, but a striking asymmetry should be flagged for follow-up.