Sensorimotor rhythm
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SMR waves

Description

The Sensory Motor Rhythm (SMR) is also called Mu rhythm^{citation needed} (find a more detailed article there). It is an oscillatory idle rhythm of synchronized electromagnetic brain activity. It appears in spindles in recordings of EEG, MEG, and ECoG over the sensoryimotor cortex. For most individuals, the frequency of the SMR is in the range of 8 to 14 Hz.

Meaning

The meaning of SMR is not fully understood. Phenomenologically, a person is producing a stronger SMR amplitude when the corresponding sensory-motor areas are idle, e.g. during states of immobility. SMR typically decrease in amplitude when the corresponding sensory or motor areas are activated, e.g. during motor tasks and even during motor imagery.¹

Conceptually, SMR is sometimes mixed up with alpha waves of occipital origin, the strongest source of neural signals in the EEG. One reason might be, that without appropriate spatial filtering the SMR is very difficult to detect as it is usually superimposed by the stronger occipital alpha waves.

Relevance in research

Neurofeedback

Neurofeedback training can be used to gain control over the SMR activity. Neurofeedback practitioners believe - and have produced experimental evidence to back up their controversial claims² - that this feedback enables the subject to learn the regulation of the own SMR. People with learning disabilities,³ ADHD,⁴ epilepsy,⁵ and autism^{citation needed} may benefit from an increase in SMR activity via neurofeedback. In the field of Brain-Computer Interfaces (BCI), the deliberate modification of the SMR amplitude during motor imagery can be used to control external applications ⁶.

See also

• Electroencephalography
• Delta wave
• Theta wave
• Alpha wave
• Beta wave
• Gamma wave

References

1. ^ Ernst Niedermeyer, Fernando Lopes da Silva Electroencephalography. Basic principles, Clinical Applications and Related Fields. 3rd edition, Williams & Wilkins Baltimore 1993
2. ^ Tobias Egner and M. Barry Sterman, “Neurofeedback treatment of epilepsy: From basic rationale to practical application,” in press
3. ^ PMID 6542077
4. ^ Vernon, David; Tobias Egner, Nick Cooper, Theresa Compton, Claire Neilands, Amna Sheri and John Gruzelier (January 2003). "The effect of training distinct neurofeedback protocols on aspects of cognitive performance". International Journal of Psychophysiology 47 (1): 75–85. doi:10.1016/S0167-8760(02)00091-0. 
5. ^ Egner, Tobias; M Barry Sterman (February 2006). "Neurofeedback treatment of epilepsy: from basic rationale to practical application". Expert Review of Neurotherapeutics (Future Drugs) 6 (2): 247–257. doi:10.1586/14737175.6.2.247. 
6. ^ Andrea Kübler and Klaus-Robert Müller. An introduction to brain computer interfacing. In Guido Dornhege, Jose del R. Millán, Thilo Hinterberger, Dennis McFarland, and Klaus-Robert Müller, editors, Toward Brain-Computer Interfacing, pages 1-25. MIT press, Cambridge, MA, 2007

Further reading

• Robbins, Jim (2000). A Symphony in the Brain. 
• M. B. Sterman and W. Wyrwicka, “EEG correlates of sleep: Evidence for separate forebrain substrates,” Brain Research, vol. 6, 1967, pp. 143–163.
• W. Wyrwicka and M. B. Sterman, “Instrumental conditioning of sensorimotor cortex eeg spindles in the waking cat,” Physiology and Behavior, vol. 3, 1968, pp. 703–707.
• Warren, Jeff (2007). "The SMR", The Head Trip: Adventures on the Wheel of Consciousness. ISBN 978-0679314080. 

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