Essentials of Electroencephalography Groundwork
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Transcript of Essentials of Electroencephalography Groundwork
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