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EEG
Slide 05F.1
Electroencephalogram
The electroencephalogram (EEG) is the
electrical signal generated by the neurons in
the brain
electro
−encephalus
−
electrical
brain
Copyright © by A. Adler, 2009 -2014 (including Material from J.G. Webster)
graph

writing, ie. signal
EEG
Slide 05F.2
EEG
Electroencephalography (EEG) is the
measurement of electrical activity
produced by the brain as recorded from
electrodes placed on the scalp.
EEG measurements on

Scalp 100uV (scalp is highly insulating)

Cortex (10mV)

Depth (electrodes into brain) as part of
surgery
Electrical activity from brain is much more
complex. In general, we see a
summation of >1m neurons. Thus EEG
is a ‘heuristic’ field.
Copyright © by A. Adler, 2009 -2014 (including Material from J.G. Webster)
EEG measurement
electrodes
(source: wikipedia)
EEG
Slide 05F.3
Central Nervous System (CNS)
anatomy
Outside the CNS,
There is the

CSF: cerebrospinal
fluid

Skull
Anatomical relationship of brainstem structures (medulla oblongata, pons, midbrain,
and diencephalon (thalamus and hypothalamus)) to the cerebrum and cerebellum.
General anatomic directions of orientation in the nervous system are superimposed
on the diagrams. Here the terms rostral (toward head), caudal (toward tail), dorsal
(back), and ventral (front) are associated with the brainstem; remaining terms are
associated with the cerebrum. The terms medial and lateral imply nearness and
remoteness, respectively, to or from the central midline axis of the brain.
Copyright © by A. Adler, 2009 -2014 (including Material from J.G. Webster)
EEG
Slide 05F.4
Types of EEG
Two basic types of EEG signals

Evoked Potentials
A stimulus is provided, and the EEG response measured. Allows removing other
activity by averaging “out of phase” signals.


VER – visually evoked response

AER – auditory evokes response
Resting Rhythms – “brain waves”

Mostly irregular patterns from brain, but sometimes form structured patterns that
have been classified

Alpha – quiet awake - 8-13 Hz

Beta - intense mental activity – 14-30 Hz

Theta – Children & distressed adult – 4-7 Hz

Delta – Deep sleep & infancy – 2-3 Hz

REM – Sleep with dreaming

Abnormal patterns, such as epilepsy
Copyright © by A. Adler, 2009 -2014 (including Material from J.G. Webster)
EEG
Slide 05F.5
Resting Rhythms
(a) Different types of normal EEG waves. (b) Replacement of alpha rhythm
by an asynchronous discharge when patient opens eyes. (c) Representative
abnormal EEG waveforms in different types of epilepsy.
Copyright © by A. Adler, 2009 -2014 (including Material from J.G. Webster)
EEG
Slide 05F.6
EEG and Sleep
The electroencephalographic changes that occur as a human subject
goes to sleep
Copyright © by A. Adler, 2009 -2014 (including Material from J.G. Webster)
EEG
Slide 05F.7
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Questions
Why are EEG signals on the surface of the scalp so
small? Why are the brain neuronal signals obtained
with needle electrodes so much larger?
How accurately is it possible to know the thoughts in
the brain from the EEG signals?
The ECG is described as a vector field? Why not the
EEG?
What is the frequency content of EEG signals? Is this
lower of higher than ECG / EMG?
Why do EEG signals not appear to be stochastic noise
like EMG signals?
Copyright © by A. Adler, 2009 -2014 (including Material from J.G. Webster)