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| 4.
BCI - Brain–computer interfaces |
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4.2. Present-day BCIs
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4.2.4. Mu and beta rhythms |
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In
awake people, primary sensory or motor cortical areas often
display 8–12 Hz EEG activity when they are not engaged in processing
sensory input or producing motor output.
This idling activity is called mu rhythm when
focused over somatosensory or motor cortex and visual
alpha rhythm when focused over visual cortex.
mu-rhythm activity comprises a variety of different 8–12 Hz
rhythms, distinguished from each other by location, frequency,
and/or relationship to concurrent sensory input or motor output.
These mu rhythms are usually associated with 18–26 Hz beta rhythms.
While some beta rhythms are harmonics of mu rhythms, some are
separable from them by topography and/or timing, and thus are
independent EEG features.
mu and/or beta rhythms could be good signal features for EEG-based
communication. They are associated with those cortical areas
most directly connected to the brain’s normal motor output channels.
Movement or preparation for movement is typically accompanied
by a decrease in mu and beta rhythms.
This decrease has been labeled 'event-related
desynchronization' or ERD.
Rhythm increase after movement and with relaxation.
This increase has been labeled 'event-related
synchronization' (ERS).
ERD and ERS do not require actual movement, they occur
also with motor imagery (i.e. imagined movement).
Source:
Brain–computer
interfaces for communication and control, Clinical Neurophysiology
113 (2002) 767–791, Jonathan R. Wolpaw, Niels Birbaumer, Dennis
J. McFarland, Gert Pfurtscheller, Theresa M. Vaughan |
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