Treatments for tremor disorders have largely focused on the prescription of medications or, in more severe cases, brain surgery (for a review see Schneider & Deuschl 2015). In recent years, there have been some novel – and at times ‘sci-fi’ – approaches to reducing tremor amplitude. Such approaches include the use of an exoskeleton worn over the arm and hand (Roco et al. 2006), or the application of rhythmic electrical stimulation to muscles (Dosen et al. 2014).
Recently, Trenado and colleagues (2014) have published a scientific paper in PLOSone on the successful use of a special type of vibratory stimulation to suppress tremor. The study was performed on a group of 8 individuals with enhanced physiological tremor who were asked to perform simple visuomotor task: modulate the amount of force generated by the index finger in response to a visual target presented on a computer monitor and small force perturbations applied to the finger.
In their study, Trenado and colleagues (2014) added small amplitude mechanical stochastic noise to dampen the tremor. Stochastic noise is a fancy term for a type of vibration that is the sum of many frequencies, which in the present study was 3-35Hz. Stochastic resonance is a phenomenon whereby the transfer of information is maximized by the addition of stochastic noise. For example, the addition of stochastic noise has been shown to enhance sensation from the cutaneous receptors in the fingertips as well as the muscle spindles in our muscles (Collins et al. 1996; Cordo et al. 1996). One of the problems with tremor is that oscillations in the central and peripheral nervous system generate rhythmical activity in muscles, which manifests itself as tremor in the joints of the body that ‘prefer’ to oscillate at the same frequency. This is called mechanical resonance and is the reason the Tacoma Narrows bridge collapsed and why opera signers can break a crystal glass with their voice. The ‘trick’ used by Trenado and colleagues (2014) was to test stochastic noise of different amplitudes in order find the one that had the worst resonance, which is to say the one that lead to the largest decrease in tremor amplitude.
WHAT DID THEY FIND?
All subjects who participated in the study experienced an improvement in the visuomotor task and a reduction in tremor amplitude and tremor-related muscle activity when the vibratory stimulation with the worse stochastic resonance. By far the coolest finding in the study was that all subjects reported a reduction in tremor amplitude that far outlasted the application of the vibration. Specifically, one subject reported after-effects that lasted ~15h, two subjects reported benefits that lasted ~8h and the other six subjects reported after-effects that lasted between 3-6h.
SIGNIFICANCE AND IMPLICATIONS
The finding present by Trenado and colleagues (2014) are very promising. However, their study had a small sample size and was limited to isolated finger tremor and a non-functional task. Whether the benefits of stochastic noise reported in this study will transfer over to individuals with more severe forms of tremor and more functional tasks remains to be seen. Nevertheless, these results – especially the prolonged after-effects experienced by the study participants – are a very exciting development for those living with tremor.
Trenado C, Amtage F, Huethe F, Schulte-Mönting J, Mendez-Balbuena I, Baker SN, Baker M, Hepp-Reymond MC, Manjarrez E, Kristeva R (2014). Suppression of Enhanced Physiological Tremor via Stochastic Noise: Initial Observations. PLoS One 9, e112782.
Collins JJ, Imhoff TT, Grigg P (1996). Noise-enhanced tactile sensation. Nature 383, 770.
Cordo P, Inglis JT, Verschueren S, Collins JJ, Merfeld DM, Rosenblum S, Buckley S, Moss F (1996). Noise in human muscle spindles. Nature 383, 769-70.
Dosen S, Muceli S, Dideriksen J, Romero J, Rocon E, Pons J, Farina D (2014). Online Tremor Suppression Using Electromyography and Low Level Electrical Stimulation. IEEE Trans Neural Syst Rehabil Eng. Jul 15 [Epub ahead of print].
Schneider SA, Deuschl G (2015). Medical and Surgical Treatment of Tremors. Neurol Clin 33, 57-75.
Rocon E, Ruiz AF, Brunetti F, Pons JL (2006), On the use of an active wearable exoskeleton for tremor suppression via biomechanical loading. IEEE International conference on robotics and automation, Orlando, Florida, pp.3140-3145.