Essentials ofElectroencephalography

Groundwork

Jarrod BlinchMay 17th, 2011

Comprehensive presentation

Overview

• Overall goal• Physics-EEG interface• Potentials• Rhythms• Fallacies• Recording• Artifacts• Processing…

Overall goal

• Connect psychology with physiology• EEG has been linked to psychology

Physics-EEG interface

Potentials• Spontaneous– Uncorrelated with the occurrence of an experimental condition

• Induced– Correlated with experimental conditions but not strictly phase-

locked to its onset• Evoked– Strictly phase-locked to the onset of an experimental condition

across trials• Emitted– In response to omitted stimuli

RhythmsName Symbol Frequency

bandExamples

Delta δ 0-4 Slow-wave sleep

Theta θ 4-8 Working memory

Alpha α 8-12 Thalamic pacemaker, memory processes, attention, visual awareness

Beta β 12-30 Suppressed during motor action, imagined movements, nerve stimulation

Gamma γ 30-~70 Binding phenomena, perceiving meaningful objects, attention

Omega ω ~60-120 Retinal origin

Rho ρ ~250 Hippocampal ripples

Sigma σ ~600 Thalamocortical bursts

Fallacies

• EEG is an epiphenomenon• EEG practice divorced from theory• Artifact-free data• EEG versus MEG• Data reduction

EEG versus MEG

• EEG and MEG measure the same dipoles• MEG is more accurate than EEG• Results with one can be checked with the

other• MEG is better because it is reference free

Data reduction

• EEG is contained in the raw data and nothing is added by computer transformation

• Adding more electrodes beyond the standard 10/20 system provides no useful information

• New data analysis methods in search of application

Overview

• Overall goal• Physics-EEG interface• Potentials• Rhythms• Fallacies• Recording• Artifacts• Processing…

Recording

• Clean data• Active and reference electrodes• Noise• Electrodes and impedance• Digitisation• Filtering

Clean data

Active and reference electrodes

Noise• AC line current (60 Hz)

– Shielded or use DC• Monitor (60-120 Hz)

– Faraday cage• Movement

– Relax, drop the jaw• EMG (10-1000 Hz)• EKG (1.0-1.4 Hz)• Pulse-wave• Electrodes• Alpha waves (6-12 Hz)• Skin potentials…

Electrodes and impedance

• Why skin impedances below 5 kΩ?– Common-mode rejection– Skin potentials

Digitisation

• Amplifier– Gain– Resolution

• Nyquist theorem

Filtering

• Filters can substantially distort data• Essential to reduce noise– Aliasing, low-pass– Skin potentials, high-pass (.01 Hz)

Artifact rejection

Processing…

• Event-related potentials (Tues, May 31st, 2 pm)• Principal component analysis• Independent component analysis (June)• Cortical dynamics (June)

Osman & Moore (1993). The locus of dual-task interference: Psychological refractory effects on movement-related brain potentials. Journal of Experimental Psychology: Human Perception and Performance, 19(6), 12-92-1312.- Experiment 1, just 10 pages

Luck (1998). Sources of dual-task interference: Evidence from human electrophysiology. Psychological Science, 9(3), 223-227.- Experiment 1, only 3 pages