Brain–Computer Interfaces - Index of

Dynamics of Sensorimotor Oscillations in a Motor Task 53
Fig. 4 Examples of activation patterns obtained with functional magnetic resonance imaging
(fMRI) and EEG (ERD/ERS) during execution and imagination of hand (right panel) and foot
movements (left panel). Note the correspondence between the focus of the positive BOLD signal
and ERD on the one side, and between the negative BOLD signal and ERS on the other side
The opposite phenomenon, the enhancement of central mu rhythm and blocking of
occipital alpha rhythm during visual stimulation, was documented by Koshino and
Niedermeyer [51] and Kreitmann and Shaw [52]. Figure 4 shows further examples
demonstrating the intramodal interaction, in terms of a hand area ERD and foot area
ERS during hand movement and hand area ERS and foot area ERD during foot
movement, respectively.
The focal mu desynchronization in the upper alpha frequency band may reflect
a mechanism responsible for focusing selective attention on a motor subsystem.
This effect of focal motor attention may be accentuated when other cortical areas,
not directly involved in the specific motor task, are “inhibited”. In this process, the
interplay between thalamo-cortical modules and the inhibitory reticular thalamic
nucleus neurons may play an important role ([44, 53]).
Support for the “focal ERD/surround ERS” phenomenon comes from regional
blood flow (rCBF) and functional magnetic resonance imaging (fMRI) studies.
Cerebral blood flow decreases in the somatosensory cortical representation area
of one body part whenever attention is directed to a distant body part [54]. The
BOLD (Blood Oxygen Level Dependent) signal also decreased in the hand motor
area when the subject imagined or executed toe movements [36]. In this case, attention
was withdrawn from the hand and directed to the foot zones, resulting in a
positive BOLD response in the foot representation area. Figure 4 shows this antagonistic
behavior in hemodynamic (fMRI) and bioelectrical (EEG) responses during
hand and foot movements. Imagined movements are also called covert movements,
and real movements are called overt movements. A task-related paradigm (covert
movements over 2 s) was used for the fMRI, and an event-related paradigm (overt
or covert movements in intervals of approximately 10 s) was used for the EEG.
An fMRI study during execution of a learned complex finger movement sequence
and inhibition of the same sequence (inhibition condition) is also of interest. Covert
movement was accompanied by a positive BOLD signal and a focal mu ERD in the
hand area, while movement inhibition resulted in a negative BOLD signal and a mu
ERS in the same area [55, 56].