Biomedical Engineering Reference
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sidered as EEG indicators of motor cortex and adjacent somatosensory cortex func-
tions [49]. When the subject is performing a limb movement, thinking about a limb
movement, or receiving a tactile/electrical stimulation on a limb, a prominent atten-
uation of ongoing mu rhythm can be observed over the rolandic area on the
contralateral hemisphere [47, 48].
Following Pfurtscheller's classical work in the 1970s [50], this SMR attenuation
is usually termed event-related desynchronization (ERD), whereas the increases in
SMR amplitude are termed event-related synchronization (ERS). Moreover, the spa-
tial distribution of ERD/ERS is closely related to the body map on the sensorimotor
cortex. For example, the left hand and right hand produce the most prominent
ERD/ERS pattern in the corresponding hand area in the contralateral sensorimotor
cortex (Figure 8.6).
Thinking about, or imagining, a limb movement generates SMR patterns that
are similar to those generated during real movement. These real/imagined move-
ment patterns make up the physiological basis for SMR-based BCI (in some of the
literature, this is also termed motor imagery-based BCI, or mu rhythm-based BCI)
[13, 47, 48, 51].
In recent years, BCI systems based on classifying single-trial EEGs during motor
imagery have developed rapidly. Most of the current SMR-based BCIs are based on
characteristic ERD/ERS spatial distributions corresponding to different motor
imagery states, such as left-hand, right-hand, or foot movement imagination. The
first motor imagery-based BCI was developed by Pfurtscheller et al. and was based
on the detection of EEG power changes caused by ERD/ERS of mu and beta rhythms
during imagination of left- and right-hand movements [47]. As shown in Figure 8.6,
for example, imagination of left-hand movement causes a localized decrease of
Cz
Cz
C3
C4
C4
foot
Foot
Right
hand
Left
hand
Tongue
Tongue
Tongue
Tongue
(a)
(b)
C3
C4
Right
hand
Figure 8.6
Basic principle of SMR-based BCI. (a) Approximate representation areas of body parts
shown in the coronal section of the sensorimotor cortex; (b) position of C3/C4 electrode on the scalp;
and (c) typical EEG (bandpass filtered at 4 to 30 Hz, covering the mu and beta bands) during imagi-
nation of left- or right-hand movement, which shows a distinct temporal pattern on the C3/C4
electrode.
Left
hand
Right
hand
Left
hand
Right
hand
Left
hand
Right
hand
Left
hand
(c)
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