Transcript Electroenceplalograph and The Hemodynamic Response

Electroencephalography
Collecting and Analyzing Data: 101
Timothy M. O’Keefe1
1Olin
Neuropsychiatry Research Center
E.E.G.
EEG is a recording (graph) of electrical signals (electro)
from the brain (encephalo).
Brain Electricity:
a.k.a. Electrical Potentials (EP)
The structure and chemical composition of neurons (or
brain cells) leads to the generation of an electrical
potential (without IPSP), which is a relative
difference in electrical charge across the nerve cell
membrane
EEG has the ability to measure this electrical activity
during normal and pathological states.
Obtaining EEG data consists of connecting bioelectric
electrodes from the scalp (or exposed brain) into a
machine capable of amplifying these microvolt (µv)
signals so that they may be recorded on paper or
recorded digitally.
*Hurdling noisy EEG: Because action potentials are so
small, electrical interference, called artifacts, from
outside sources (motors, overhead lights and even
eye blinking) is often as strong as the signals EEG is
trying to detect. When analyzing EEG data,
researchers need to have some way to distinguish
artifacts from brain activity and to decode the
brain’s electrical rhythms.
The History of EEG
1875 – Richard Caton from Jena, Germany
discovered electrical brain activity by probing
the surface of exposed brains of animals using
a primitive version of the galvanometer.
1920’s – Hans Berger recorded human EEG with
string galvanometers using subjects with
holes in their skulls. He discovered waves at
10 Hz (named them Alpha waves because
they were the first he isolated in the human
EEG).
Dr. Hans Berger
Recording EEG: The Ancient Way.
An action potential occurs.
Electricity is sent out of the
electrode, into one end of the
wire and through the coil.
Coil becomes a magnet itself and
experiences a deflecting torque
from surrounding U-shaped
magnet.
Spring (in the incoming end of
the wire) creates a restoring
torque (restoring coil to original
or resting position).
Other end of wire moves and
writes.
Why is EEG Important?
What You Can Do!
How are you supposed to say what neuron, or what
system of neurons are making all that noise? You
can’t [save your DSA questions], fMRI can… but
then again fMRI is not even looking at electricity,
fMRI is looking at blood oxygen level.
Even then MRI takes 30 slices of the brain every,
(depending on your scanner) 1-3 seconds. EEG
can observe electrical activation from 0s to 1s in
milliseconds.
Recording EEG: The Present Way
Null modem port 2
Port 1
Serial cable from VAPP to CIRC
Modified parallel cable from CIRC to Dig Box
VAPP
CIRC
Digital cable from Dig Box to Intel Box
Amp to Dig Box
Digitize
Fake Brain
Amp to Headbox
64 Channel: 10/20 System
Pivik et al. 1993
EEG Analysis with ERPSS
ERPSS – Event Related Potential Statistical Software
stimulus
Action potential
Normalized & Averaged Data
What your data looks like after it has been
filtered for noise, choped up in terms
of 200ms - 300ms following a
declared stimuli and then averaged (all
occurrences of that stimuli and a
response following is then averaged
together.)
Merps
Merps is a program used to look at specific points within multiple waves of multiple
subjects so that it may be statistically said that, “this is the amount of variability
between what should have been the same wave at these defined points.” Also, merps
allows one to create graphs of data points so that variability may be observed visually.
Example: What is the average variability between this
exact point on the same channel in subject 1 and 2.