Measuring Vestibular Organ Function With Weak Alternating Current Stimulation

The participants will each attend one experimental session consisting of multiple short (1-3 min) measurement trials. During a trial the participant's vestibular system is stimulated with a transcranial electrical stimulator device and their movements are recorded with a force plate and acceleration sensors.

The goal of the study is to collect and analyse data from 30 research participants with diagnosed vestibular disorders.

• Active transcranial electrical vestibular stimulation (Active EVS) (Device): Active transcranial electrical vestibular stimulation (EVS) with alternating current (maximum peak current below 2 mA and stimulation frequency 2-20 Hz) applied for 1-3 minutes at a time and for under 20 minutes in total. EVS will be applied either bilaterally (ear to ear) or unilaterally (left ear to neck or right ear to neck). The participants movements during the stimulation are measured with a force plate and wearable acceleration sensors. The study uses multiple types of vestibular stimulation waveforms which are applied in a randomized sequence, such that neither the participant nor the investigator know the exact stimulation type at the time of the measurement.
• Sham transcranial electrical vestibular stimulation (Sham EVS) (Device): Sham (no current) transcranial electrical vestibular stimulation applied for 1-3 minutes. The participant's movements during the supposed stimulation are measured with a force plate and wearable acceleration sensors. Neither the participant nor the investigator know at what point of the intervention sequence the sham stimulation is applied.
• Control measurement (Device): The participant's movements are measured with a force plate and wearable acceleration sensors for the same time duration (1-3 min) and following the same protocols as in other interventions, but both the participant and the investigator know that no stimulation is being applied. The control measurement will always be completed before all other interventions and is not part of the randomized intervention sequence.

Primary outcomes

• Changes in the frequency content of the movement response signals [From study appointment to the analysis of the results (up to 12 months)]: Changes of the power in a frequency band of 0-20 Hz in the measured movement response signals during active electrical vestibular stimulation (EVS). The measured movement response signals are force plate Center of Pressure (CoP) and 3-axis acceleration data from wearable acceleration sensors.

Secondary outcomes

• Latency of the EVS response [From study appointment to the analysis of the results (up to 12 months)]: Latency of the EVS-induced movement response measured as the time delay between the stimulation and the measured movement.
• Highest frequency of the EVS-induced response [From study appointment to the analysis of the results (up to 12 months)]: Highest frequency at which EVS induces a response determined via spectral analysis of the movement data

Sex: All, ages: 18 Years to 70 Years

Inclusion Criteria:

* Signed informed consent form
* One of the following: clinically diagnosed vestibular schwannoma, vestibular neuritis, or simultaneous unilateral hearing loss and vestibular dysfunction.

Exclusion Criteria:

* History of epilepsy or seizures
* Past brain surgery
* Pacemaker, cochlear implant, or other implanted medical device
* Pregnancy
* Skin problems or damaged skin at the site of the stimulation (scalp and neck)

• Ilkka Laakso, D.Sc. (Tech), Principal investigator, Aalto University
• Topi Jutila, MD, PhD, Principal investigator, HUS Helsinki University Hospital