The sensorimotor rhythm (SMR) is brain wave rhythm. It is an oscillatory idle rhythm of synchronized electromagnetic brain activity. It appears in spindles in recordings of EEG, MEG, and ECoG over the sensorimotor cortex. For most individuals, the frequency of the SMR is in the range of 13 to 15 Hz.
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.
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. The feline SMR has been noted as being analogous to the human mu rhythm.
Relevance in research
Neurofeedback training can be used to gain control over the SMR activity. Neurofeedback practitioners believe—and have produced experimental evidence to back up their claims—that this feedback enables the subject to learn the regulation of their own SMR. People with learning difficulties, ADHD, epilepsy, and autism 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.
- Delta wave – (0.1 – 3 Hz)
- Theta wave – (4 – 7 Hz)
- Alpha wave – (8 – 15 Hz)
- Mu wave – (7.5 – 12.5 Hz)
- SMR wave – (12.5 – 15.5 Hz)
- Beta wave – (16 – 31 Hz)
- Gamma wave – (32 – 100 Hz)
- Arroyo, S.; Lesser, RP.; Gordon, B; Uematsu, S; Jackson, D; Webber, R (1993). "Functional significance of the mu rhythm of human cortex: an electrophysiologic study with subdural electrodes". Electroencephalography and Clinical Neurophysiology 87 (3): 76–87. doi:10.1016/0013-4694(93)90114-B. PMID 7691544.
- Ernst Niedermeyer, Fernando Lopes da Silva Electroencephalography. Basic principles, Clinical Applications and Related Fields. 3rd edition, Williams & Wilkins Baltimore 1993
- Tobias Egner and M. Barry Sterman, “Neurofeedback treatment of epilepsy: From basic rationale to practical application,” in press
- Tansey MA (February 1984). "EEG sensorimotor rhythm biofeedback training: some effects on the neurologic precursors of learning disabilities". Int J Psychophysiol 1 (2): 163–77. doi:10.1016/0167-8760(84)90036-9. PMID 6542077.
- 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. PMID 12543448.
- 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:10.1586/1473722.214.171.124. PMID 16466304.
- Pineda, Jaime; Brang, D., Hecht, E., Edwards, L., Carey, S., Bacon, M., Futagaki, C., Suk, D., Tom, J., Birnbaum, C., and Rork, A. (2008). "Positive behavioral and electrophysiological changes following neurofeedback training in children with autism". Research in Autism Spectrum Disorders 2 (3): 557–581. doi:10.1016/j.rasd.2007.12.003.
- 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
- Robbins, Jim (2000). A Symphony in the Brain. ISBN 0-87113-807-7.
- Sterman, M. B.; Wyrwicka, W. (1967). "EEG correlates of sleep: Evidence for separate forebrain substrates". Brain Research 6 (1): 143–163. doi:10.1016/0006-8993(67)90186-2. PMID 6052533.
- Wyrwicka, W.; Sterman, M. B. (1968). "Instrumental conditioning of sensorimotor cortex eeg spindles in the waking cat". Physiology and Behavior 3 (5): 703–707. doi:10.1016/0031-9384(68)90139-X.
- Warren, Jeff (2007). "The SMR". The Head Trip: Adventures on the Wheel of Consciousness. Toronto: Random House Canada. ISBN 978-0-679-31408-0.