27-12-2012, 02:22 PM
Application of Quantitative EEG to Aimaft Assessment, Management, and conbrol
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Abstract
Recent advances in the understanding
and computer processing of human
brain wave (EEG) activity have produced
renewed interest in the possibility of a bioengineering
control interface using this
signal. Evidence concerning the neurophysiological
substrates of EEG frequency
modulation and topographic expression
provide a basis for the differentiation of
functional states during vehicle control
performance. These and other studies have
identified EEGsignal components which are
subject to learned voluntary manipulation,
Progress and problems in this area of
investigation are discussed.
The control community has long
shown interest in bio-engineering interface as
a means of incorporating human biology into
the system control process. Historically,
however, this objective has been hampered
by the lack of sufficient resolution of
biological signals and the means to
adequately acquire, analyze, and integrate
such information. The rapid development of
fast, high capacity, digital processing
systems, however, is beginning to remove
the technical impediment, while recent
scientific findings provide the basis For
improved resolution of the most relevant
biological signal in this regard, the human
brain potential, as recorded by the
electroencephalogram, or EEG. Developments
in quantitative assessment of brain
electrical activity have made it possible to
scale regional cerebral engagement, and to
study differential responses to cognitive
requirements.
Neurqphysiollogical Substrates
Effective use of the EEG as a tool
for measuring brain functions stems from
accumulating evidence concerning the origins
and functional significance of this signal. It
is important that any professional seeking to
understand this field have some
comprehension of the neurophysiology on
which it is based. An extensive literature
has developed in this area, only the salient
points of which can be reviewed here. The
interested reader is directed to Steriade, et aP
(1993), McCormick (1992), and Sterman
(1995).
Communication among neurons is
mediated by electrochemical changes in the
membrane that surrounds the cell and its
axonal and dendritic processes. When at
rest, current gradients maintain a small
electrical potential across the cell membrane.
Excitatory impulses reaching the cell release
transmitter substances that can reduce, or
depolarize, this potential. If this depolarization
reaches the cell's activation
threshold, polarity is briefly reversed and the
cell discharges. Other transmitters, or the
absence of excitatory impulses in certain
cells, can increase the potential, a process
called hyoerpolarization. Since it is harder
to reach the activation threshold in this
condition, the cell is inhibited, and the
greater the hyperpolarization the greater the
inhibition.
Recent Findings
It should be pointed out that there are a
number of research groups approaching this
area of investigation from differing
conceptual perspectives and with different
technical orientations. The work to be
described here is based on the physiological
considerations discussed above, and is
perhaps unique in this regard. It is also
rooted in an extensive body of literature
which has described a pattern of EEG
rhythmic activity associated with voluntary
suppression of movements. Research
findings suggest that this is achieved via a
change in "central state" involving both the
cessation of motor programming and the
attenuation of sensory inputs related to
muscle tone and joint position. In the
appropriate central state an 11-15 Hz
rhythmic pattern which has been termed the
Sensorimotor Rhythm, or SMR, is facilitated
over the motor control (central) area of the
brain on both hemispheres. Conversely,
during motor behavior this activity is
suppressed below resting levels. The
modulation of this rhythm has been used by
several laboratories as both an index of
motor system excitability and as a signal to
control external video displays.