EEG Definitions EEG1: electroencephalogram—i.e., the “data” EEG2: electroencephalographic—i.e., the “equipment” EEG3: electroencephalography—i.e., the “technique”

states of consciousness

EEG Strengths Non-invasive Assesses “system-level” states Millisecond time-scale resolution Signals add linearly (i.e., the whole = the sum of its parts) Low cost (relative to MEG, PET, fMRI) Simple to use

EEG Weaknesses An Analogy... Electrode more sensitive to proximal neurons The CSF distorts/smears the electric fields/potentials The skin, skull, and meninges distorts the E-fields You’re blind to certain activity if it isn’t persistent/correlated in time/space

EEG Weaknesses—The Analogy Stairwell  EEG People  Neurons Singing  Neural Activity Reverberant Quality  CSF (distortion of scalp potentials) Door  Skin, Skull, Meninges (distortion of scalp potentials) Microphone  Electrode (proximity effects) The EEG is a highly distorted and incomplete representation of true neural activity

EEG: The Technique

EEG: Continuous (Raw) Data

10-20 system - electrodes positioning (monopolar montage) …the reason why a cap is useful…

Origin of the signal - noninvasive measurement - direct measurement. skull CSF tissue MEG EEG B orientation of magnetic field recording surface scalp current flow - noninvasive measurement - direct measurement.

requires sensitive detectors (low noise-high gain amplification) How small is the signal? Earth field Intensity of magnetic signal(T) EYE (retina) Steady activity Evoked activity LUNGS Magnetic contaminants LIVER Iron stores FETUS Cardiogram LIMBS Steady ionic current BRAIN (neurons) Spontaneous activity Evoked by sensory stimulation SPINAL COLUMN (neurons) HEART Cardiogram (muscle) Timing signals (His Purkinje system) GI TRACK Stimulus response Magnetic contaminations MUSCLE Under tension Urban noise Contamination at lung Heart QRS Biomagnetism Fetal heart Muscle Spontaneous signal (a-wave) requires sensitive detectors (low noise-high gain amplification) Signal from retina Evoked signal Intrinsic noise of SQUID

origin of EEG signals (1) afferent inputs excitatory pyramidal cortical neurons + current source - current sink + - dipole amplifier macroscopic depolarization ~V ref

origin of EEG signals (2) resistance low conductor

from neurophysiology to electrophysiology (1) What is recorded with EEG? synchronized neural populations - transmembrane currents of pyramidal neurons apical dendrites Why not action potentials? spike vs. dendritic currents - synchronization dendritic electrical dipoles vs. AP propagation - cancellation spike rate vs. dendritic time constant - duration

what is being recorded and what is not Closed-fields cancellation Open fields

EEG: Continuous (Raw) Data

Epoching

Signal Averaging

Emergence of the ERP

The ERP: Amplitude and Latency

The Broadband Response

Filtering: Filter Types

induced vs.phase-locked responses BOTH are stimulus-driven induced rhythm vs. locked response

Characteristic Auditory Evoked Related Potentials

Hillyard

Updating, transient memory spectral EEG Characteristic Bands Frequency Range Correlates (?) Delta  2 – 4 Hz sleep Theta  4 – 7 Hz memory Alpha 1 8 – 10 Hz sensory, attention (more A) 2 10 – 12 Hz (more V) Beta 1 12 – 18 Hz ? 2 18 – 25 Hz Mu/motor Gamma Phase-locked  25 – 35 Hz Updating, transient memory Induced  35 – 80 Hz Cognitive binding

•power spectrum •bandpass filtering

The 40-Hz “Driven” Response (BPF)

Driven Responses

The Evoked Gamma Band Response

Evoked GBR Properties Total Duration: ~100 ms Cycle Duration: ~ 25 ms Spectral Energy Range: ~25-75 Hz Latency: ~ 50 ms Amplitude: < 1 uV Generator Source: Cortex (MEG Studies) Generated by stimulus onset