Electroencephalography Collecting and Analyzing Data: 101 Timothy M. O’Keefe 1 1 Olin Neuropsychiatry Research Center.

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

VAPP CIRC

Digitize

Fake Brain

Serial cable from VAPP to CIRC

Modified parallel cable from CIRC to Dig Box

Digital cable from Dig Box to Intel Box

Amp to Headbox

Amp to Dig Box

Port 1

Null modem port 2

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.)

MerpsMerps 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.