Electroencephalography and Event-related potentials in Clinics (Clinical EEG , ERP)

Electroencephalography & Event-related potentials

(EEG & ERP)

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EEG

ERPBCI ERPSchizophreniaMood disorders Alcohol dependence and substance abuseDementia Traumatic brain injuryNormal development Childhood disordersADHDLearning Disorders

Research and ApplicationPsychological ResearchNeurological ResearchMedical ResearchEducational Research and ApplicationTherapeutic ApplicationOccupational Application

Electroencephalography (EEG)Electrocorticogram (ECoG)Local field potential or single neuron

Magnetoencephalography (MEG)Positron emission tomography (PET)Magnetic resonance imaging (fMRI)Infrared (IR) imaging

5 mm5 mm8

When a neuron is active, its voltage may change by 100 mV or more.

Electrical activity in a single neuron.How do EEGs work? Neural communication produces electrical activity. 8Large amplitudes tend to entrain many neurons

Inhibition Minimum MaximumTimeCell 2Cell 1Cell 3Cell 1Cell 2Cell 3Excitation (Pyramidal cells)Maximum MinimumBasics: Inhibition, Amplitude and TimingCortical Basis of Scalp EEG

Baillet et al., IEEE Sig. Proc. Mag., Nov 2001, p. 16. Six Layer Cortex

Mountcastle, Brain, 120:701-722, 1997.Head Tissue Layers

EEG Electrodes

Sliver ElectrodesElectrodes Cap14

This activity may be detectable to electrodes on the scalp.

How do EEGs work? Conventional electrode caps from EGI, Neuroscan, and Electro-Cap.14 Hardware costs are significantly lower than those of all other techniques EEG sensors can be used in more places than fMRI, SPECT, PET, MRS, or MEG, EEG has higher temporal resolution - milliseconds, rather than seconds - it can, in fact, take as many as 2000 samples per second (Only MEG rivals these speeds)EEG is relatively tolerant of subject movementEEG is silentEEG does not aggravate claustrophobiaEEG does not involve exposure to high-intensity (>1 Tesla) magnetic fieldsERP studies can be conducted with relatively simple paradigms, compared with block-design of fMRI studiesExtremely uninvasive

Significantly lower spatial resolution. fMRI, for example, can directly display areas of the brain that are active, while EEG requires intense interpretation just to hypothesize what areas are activated by a particular response. EEG determines neural activity that occurs below the upper layers of the brain (the cortex) very poorly. Unlike PET and MRS, cannot identify specific locations in the brain at which various neurotransmitters, drugs, etc. can be found. Often takes a long time to connect a subject to EEG, as it requires precise placement of dozens of electrodes around the head and the use of various gels, saline solutions, and/or pastes to keep them in place. Signal-to-noise ratio is very poor, so sophisticated data analysis and relatively large numbers of subjects are needed to extract useful information from EEG a given electrode on the scalp does not record solely the neuronal activity directly underlying it. Rather, every electrode picks up signals from different sources that can eventually be quite distalFluctuation of the voltage at the reference electrode will lead to changes of the potential at the active electrode even if the voltage at that point was actually stable. There is no point that is electrically silent and could be considered as true zero potential.

EEG Recording From Normal Adult Male19/37

MidlineFronto-centralCentro-parietalAnteriorPosterior20

PCs 1-8

10 /20 % system of EEG electrode placement

Different types of brain waves in normal EEGAlpha waverhythmic, 8-13 Hzmostly on occipital lobe20-200 Vnormal,relaxed awake rhythm with eyes closed

Beta waveirregular, 14-30 Hzmostly on temporal and frontal lobemental activityexcitement

Theta waverhythmic, 4-7 HzDrowsy, sleep

Delta waveslow, < 3.5 Hzin adultsnormal sleep rhythm

Different types of brain waves in normal EEGRhythmFrequency(Hz)Amplitude(uV)Recording& LocationAlpha()8 1350 100 Adults, rest, eyes closed.Occipital regionBeta()14 - 3020 Adult, mental activityFrontal regionTheta()5 7 Above 50Children, drowsy adult, emotional distressOccipitalDelta()2 4 Above 50Children in sleepD T A B EEG brain waves in the Sleep Cycle:

Fourier Domain

EEG recording in man

Eyes opened condition.Examples of different waves.The cocktail party problem - find Z

Az1z2zNXTZTXT=AZTx1x2xNBlind Source SeparationBlind Source Separation deals with the separation of a mixture of sources, with a little prior information about the mixing process and the sources signals......SensorsS1S2

SNSourcesEnvironmentSource Separation AlgorithmW......x2xNx1 12NObservationsx = As = WxNyquist Theorem

The highest frequency which can be accurately represented is one-half of the sampling rate.The sampling rate here is below the Nyquist frequency, so the result of sampling is nothing like the input:aliasing.For practical purposes the sampling rate should be 10 higher than the highest frequency in the signal.

Two dimensional example

38First PC lies along the axis of maximum variance.Second PC is constrained to be orthogonal to first.

39Are there basis functions that better describe the variance in the data?What if we relaxed the orthogonality constraint and used a different measure of independence (not variance)?IC1 and IC2 are the independent components that ICA finds in the data projecting the data onto these axes will give you back the two sinusoids.LORETA

One such method is known as "LORETA", which provides an estimate of the current distribution throughout the entire 3-dimensional space within the brain.An example of a LORETA solution, mapped onto a normalized brain space, is provided below.04/06/11SPAN 4130 - Harry Howard - Tulane University4040http://faculty.washington.edu/losterho/erp_tutorial.htmhttp://faculty.washington.edu/losterho/images/loreta1.jpgBrain Wave Activity Delta sleep state (1-3 Hz)

Theta between sleep and awake (4-7 Hz)

Alpha relaxed state (8-12 Hz)

Low Beta focused concentration (SMR-Sensory Motor Rhythms) (12-15 Hz)

Mid-range Beta alert state (15-18 Hz)

High Beta very alert, vigilant (Above 18)

Gamma Hyper vigilant (Above 40)Default Mode NetowrkDefault-mode brainThe default network is a network of brain regions that are active when the individual is not focused on the outside world and the brain is at wakeful rest.

Working memory tasks differentially deactivate the PCC.

signal increase and spatial decrease in the PCC and a signal decrease but spatial increase in the ACC with increasing working memory load(1) Oscillations: Timing and spatial organization of information processes. Oscillations provide mechanisms that allow the emergence of spatially and temporally organized firing patterns in neural networks.

(2) Slow frequency oscillations: Conscious control of information processing. Slow frequency oscillations in the theta and alpha range (of about 4 13.5 Hz) are associated with the top-down control of two large processing systems, a working memory system and a a complex knowledge system, allowing semantic orientation in a constantly changing environment.Theta and alpha oscillations exhibit a variety of different synchronization processes (e.g., amplitude increase, phase coupling, event-related phase reorganization) that reflect different types of control processes and different aspects of the timing of cognitive processes. Oscillations and the control of information processingms poststim5006007008009001000110012001300V0.0-0.5-1.0-1.50.51.01.5FzCzPzOzTheta-waves single subject BApop -1p+1change in directionExample of an evoked, traveling theta wave, one subject, negative polarity is in blue

Alzheimers disease and mild cognitive impairmentSemantic classification task: low frequency functional connectivity between anterior (MPFC) and posterior (PCC/retrosplenial cortex) regions : negatively associated with age

eyes-closed resting state in Alzheimer patients (N=24; 9 males; mean age 76.3 years) and non-demented subjects with subjective memory complaints (N=19; 9 males)The mean level of EEG synchronization was lower in Alzheimer patients in the upper alpha (1013 Hz) and beta (1330 Hz) band. Schizophrenialow-frequency and alpha-band power abnormalities (perhaps thalamic and frontal lobe dysfunction)

augmented low-frequency power : more negative symptomslarger third ventricleslarger frontal horns of the lateral ventriclesincreased cortical sulci widthsgreater ocular motor dysfunctionAutismIn the (36 Hz) frequency rangewithin left hemisphere frontal and temporal regions810 Hz: globally reduced coherence within frontal regions and between frontal and all other scalp regions. The ASD : greater relative power between 3 and 6 Hz and 1317 Hz and significantly less relative power between 9 and 10 Hz.

P3 :

The mismatch negativity (MMN)MMN can be recorded in infants and young children

64 electrodes 256 Hz sample rate 1-45 Hz filtering 1000ms epochEEG Acquisition

Visual ERP (VEP) ( ).... ( ) ...

ERP Mood disorders Alcohol dependence and substance abuseDementia Traumatic brain injuryNormal development Childhood disordersADHDLearning Disorders Comareappearance of the MMN is a valid predictor of recovery from coma.

Based on six N100 studies (N = 548 patients)five MMN studies (N = 470)six P300 studies (N = 313)

the N100, MMN, or P300, when present, significantly predicted awakening, P300 and MMN being significantly better predictors than N100.Schizophreniareduced P300 amplitude in patients with schizophrenia (first reported 35 years ago)

The patients with schizophrenia showed smaller MMN amplitude

60 patients53 unaffected family members44 healthy controlsMood disordersdeviant P300 is less consistent in mood disorders

patient subtypes or to the severity of depression

Bipolar disorder show more consistent P300 deviations (both latency and amplitude)Alcohol dependencethe P300 amplitude reduction

degree of reduction in P300 in alcoholics was highly correlated with the number of alcohol-dependent individuals in the familyDementiabetween subcortical and cortical dementias

P300 latency distinguish dementia from depression-associated pseudodementia

Discrimination between patients with early Alzheimers disease and healthy individualsTraumatic brain injuryReduction in the amplitude of visual P300 in survivors of traumatic brain injury in approximately half of the studies

Most frequent effect of traumatic brain injury: reduction in the amplitude of auditory P300Traumatic brain injury

Developmental changes in ERPsthree-stimulus oddball (frequent standard, rare target, rare nontarget novel) frontal P3a amplitude elicited by rare novel stimuli tends to increase between the ages of 8 and 20 years.

For routine initial examination, the passive oddball may be the most useful task across a wide age rangeAttention-deficit/hyperactivity disordersmall P300 amplitudes with normal latency

a decrement in P300 at posterior electrode sites in conjunction with an augmentation at frontal sites

Other disorders of childhoodcentral auditory processing difficulties : failed to generate ERPs or substantially increased latencies and smaller amplitudes

In 11-year-old children with oppositional-defiant disorder: smaller P300 amplitudes to both cues and targets in a CPT

High-risk childrenVisual mental rotation task: P300 amplitude was smaller for young boys at high- compared to lowrisk for alcoholism (similar to individuals with alcohol dependence)

Lower P300 amplitudes also were observed in the pre-adolescent sons of alcoholic menDyslexiathe magnitude of the MMN reduction is correlated with the severity of dyslexia

MMN can also be employed to assess the effectiveness of dyslexia rehabilitation programs

ERP

Attentional Bias to Drug- and Stress-Related Pictorial Cues in Cocaine Addiction Comorbid with PTSD

Auditory target processing in methadone substituted opiate addicts: The effect of nicotine in controls

Behavioral Assessment & Intervention Commons4/24/2012OHSU 6-month review71

How to analyzeEEGLabBrainstormEEGLAB documentationEEGLAB Home Pagehttp://sccn.ucsd.edu/eeglab/

EEGLAB Tutorial Indexhttp://sccn.ucsd.edu/eeglab/eeglabtut.html

Workshop Home Pagehttp://sccn.ucsd.edu/eeglab/workshop/- 200 pages of tutorial (including how to for plugins) WEB or PDF : /