Use of EEG technology is shared by at least two disciplines
As EEG is used for different goals by different groups,
the same is true for other tools such as hammers
We do not require a
gavel to be
manufactured using
specifications of a
carpenter’s hammer
Standard 19 electrode positions
• Survey of 2009 EEG
papers on Medline
for humans waking
state, 25% clinical,
75% quantitative
•
Over 40,000 QEEG
papers since 1965
First QEEG paper =
1932
•
•
Dietsch (1932) analyzed EEG
using discrete Fourier transforms
(1831).
• Fast Fourier Transform (FFT)
algorithm invented (Cooley &
Tukey, 1965) , allowing practical
spectral applications
– Dumermuth & Fluhler (1967)
applied FFT to EEG
Frequency
analysis
Jean Baptiste Joseph Fourier
(1768-1830)
Energy (Amplitude) & Speed (Frequency)
SKIL Database – Individual dominant frequency
Some of the signal properties that can
be quantified
Evaluation of cortical activity. Each brain map consists of
19 electrode sites evenly spaced across the head. Color
indicates microvolts (data or raw view) or statistical
deviation from a comparison group average (stat view).
Spectral magnitude coefficients that exceed +/- 2
standard deviations are indicative of localized hyper- or
hypo-excitability in cortical neuronal pools, depending
upon the frequency of interest
SKIL Database
• Peer review
publications of SKIL
database
• Johnston et al, 2005
(Clinical EEG)
• Lorensen & Dickson,
2003 (J Neurotherapy)
•
•
•
Mean 28.2
years+/- 6.4 years
75% male
n=135 using
replicated files
from each
participant
Why amplify?
• 102 volts - Wall socket
• 10-3 volts - EKG
(millivolts)
• 10-5 volts – EOG
• 10-6 volts – EEG
(microvolts)
Sources of Artifact
• Equipment
• Computational
• Neural, non-cerebral (muscle)
• Neural, cerebral, mixed states
– alertness changes, sleep, unstable background
– transients
• Inferential
– Improper mental processes
– Improper frequency correspondence
Brain Maturation
4-8 Hz
Healthy Child
8-12 Hz
Healthy Adult
The more neurons recruited into a rhythm,
the higher the spectral magnitude (or power)
Time delay between brain areas recruited into the
same rhythm is indicated by phase
Activity and Connectivity
How to show 361 (19x19) site-pairs
Raw Data
Statistical
VIEWS
Data and Statistical (z) views
Network Maps (anterior callosotomy case)
Behavioral differences from norma
Activity
Connectivity
Frequency information
localized and shared
• Coherence
– (Wiener, 1930; Goodman, 1957; Walter, 1968)
• Comodulation
–
(Pearson, 1896; Kaiser, 1994)
Signals are …
…coherent when phase
difference is stable
…comodulated when
magnitude difference is stable