Neurostimulation of Essential Tremors

Transcutaneous Electrical Stimulation of the Median and Radial nerve in the wrist to attenuate Essential Tremors in the hand/forearm.

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JM Elek et al. described the attenuation of human wrist tremors by electrical stimulation in a paper in 1989. Recently the FDA approved a home use electrical stimulation device for the treatment of Essential Tremors (CALA Trio). Unfortunately the purchase price of this device ($3200 USD) plus the monthly maintenance cost ($157 USD) is unaffordable by many who benefit from the treatment it can provide.

Having been introduced to the current generation of microcontrollers by an old acquaintance, I decided to investigate the feasibility of building an electrical stimulus device to attenuate the amplitude of my Essential Tremors using Commercial Off The Shelf (COTS) hardware.

Essential Tremors (ET) is a neurological disorder that causes involuntary and rhythmic shaking or movement of the hands, legs, face, head, or vocal cords.  The cause of Essential or Idiopathic Tremors is still not completely understood. There is no cure for this condition and treatment is limited by a few nonspecific drugs with some undesirable side effects, neurosurgery to implant electrodes in the brain (DBS) which is costly and not without its risks, or Focused Ultrasound (MRgFUS) non-reversible ablative procedure which is not effective for all candidates, and has some noticeable side effects.

From the information found in the clinical trials of the Cala Health device, I noticed the similarity between the described electrical stimulation and the readily available TENS devices sold for the relief of pain. For the treatment of hand/forearm Essential Tremors, this electrical stimulus needed to be switched between the Median nerve and the Radial nerve at the frequency of the treated persons tremors.

Initially I used an Arduino Uno but soon exhausted its memory capacity.  The Arduino Mega2650 proved adequate for the ‘proof of concept’ stage.  A seeed studio SD card shield was used to record the data from an Adafruit LSM6DS33 9-DOF IMU.  Only the 3-axis accelerometer and the 3-axis gyroscope data was used.  The IMU was stitched to a ‘cinch strap’ so it could be accurately positioned on the back of the hand over the metacarpal of the middle finger.  Communication between the 2650 and IMU was via I2C.  A pair of 5v Solid State Relays (SSR) was used to switch the output from the TENS unit between the Median and Radial nerve.

This ‘proof of concept’ device can:

  • Measure the frequency of your postural tremor in your hand/forearm
  • Apply electrical stimulation to the Radial and Medial nerves in the forearm, alternating the stimulation at the frequency of your tremor
  • The electrical stimulus provided by a battery powered commercial TENS unit

With the followup to the proof of concept device we wanted to make improvements on portability and functionality and to remove the need for a USB  tether to a PC for user input and display.  To do this we chose the Adafruit PyGamer I was chosen because:

  • We need a better processor (ATSAMD5)  for some upcoming math calculations
  • It has its own screen
  • Buttons and a joystick for user input
  • Battery powered with a  built-in charger circuit
  • micro-SD card for data recording
  • Quiic/STEMMA connectors for I2C and digital control pins
  • Case/enclosure

Only minor pin assignment changes were required to migrate the current software to this microcontroller.

Before we move forward with any new features, we are going to merge the 2 sketches into one and build a user interface for the PyGamer screen and buttons.

Future developments include

  • Adding a graph of the tremor spectrum using discrete fourier transform
  • Add ‘phase angle’ stimulus and adjustment
  • Mount the SSR breakout board onto the PyGamer
  • Add a digital High Pass filter to remove voluntary movement signals

There are some areas of Essential Tremors that we would like to explore that will only be possible if we can analyze tremor data from multiple sources and/or for extended periods of time.  This will require community participation.

Adobe Portable Document Format - 50.70 kB - 06/14/2022 at 20:41


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