Title: The Electroencephalogram
1The Electroencephalogram
2Electroencephalogram (EEG)
- The EEG--an oscillating voltage recorded on scalp
surface - Reflects Large Neurons
- Is small voltage
- Bands of activity
- Delta 0.5-4 Hz
- Theta 4-8 Hz
- Alpha 8-13 Hz
- Beta 13-30 Hz
- Gamma 30-50 Hz
3Utility of EEG
- Relatively noninvasive
- Excellent time resolution
4Sources of scalp potentials
- Glial Cells minimal, some DC steady potentials
- Neurons
- Action Potentials NO, brain tissue has strong
capacitance effects, acting as Low Pass filter - Post-synaptic potentials YES, both inhibitory
and excitatory from functional synaptic units are
major contributors
5Alpha and Synchronization
- Why Alpha?
- It is obvious and hard to miss!
- Accounts for 70 of EEG activity in adult human
brain - From where, Alpha?
- Historically, thought to be thalamocortial
looping - Adrian (1935) demolished that theory
- Recorded EEG simultaneously in cortex and
thalamus - Damage to cortex did not disrupt thalamic alpha
rhythmicity - Damage to thalamus DID disrupt cortical alpha
rhythmicity - Thalamic rhythmicity remains even in decorticate
preparations (Adrian, 1941) - Removal of ½ thalamus results in ipsilateral
loss of cortical alpha
Next
6Alpha
7Alpha and Synchronization
- Thalamus may drive the alpha rhythmicity of the
EEG - Cortex certainly does feedback to thalamus, but
thalamus is responsible for driving the EEG - Particularly the reticularis nucleus (Steriade et
al. 1985) - Nunez (1995) has proposed that cortical neurons
regulate rhythmicity
8Recording EEG
9Recording EEG
10Electrodes, Electrolyte, Preparation
- Reduce impedance
- Ag-AgCl preferred, tin OK
- Electrolyte ionic, conductive
- Affixing
- Subcutaneous needle electrodes
- Collodion
- EC-2 paste
- Electrocap
11Recording References
- Measure voltage potential differences
- Difference between what and what else?
- Monopolar versus Bipolar
- No truly inactive site, so monopolar is a
relative term - Relatively monopolar options
- Body BAD IDEA
- Head
- Linked Ears or Mastoids
- Tip of Nose
- Hypothetical advantages of Monopolar seldom
realized
12Recording References
- Bipolar recording
- Multiple active sites
- Sensitive to differences between electrodes
- With proper array, sensitive to local
fluctuations (e.g. spike localization) - Off-line derivations
- Averaged Mastoids
- Average Reference (of EEG Leads)
- With sufficient electrodes and surface
coverage, approximates inactive site (signals
cancel out) - Artifacts average in
13Artifacts
- Three sources
- 60-cycle noise
- Muscle artifact
- Eye Movements
14Movement in reference lead
15Chewing
16Vertical eye roll
17Excessive muscle notice saturation of T5
18Talking and moving head
19Yawn
20Eye Closure and reopening
21Blink and Triple blink
22Dealing with artifacts
- 60-cycle noise
- Ground subject
- 60 Hz Notch filter
- Muscle artifact
- No gum!
- Use headrest
- Measure EMG and reject/correct for influence
- Statistically control for EMG
- Hand score
- Eye movements
- Eyes are dipoles
- Reject ocular deflections including blinks
- Computer algorithms for EOG correction
23High and low pass filtering
- Do not eliminate frequencies of interest
- Polygraphs have broad roll-off characteristics
- Digitization rate (Nyquist)
- For example, 0.01 - 100 Hz bandpass, sampled at
500 Hz
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25Time Domain Vs Frequency Domain Analysis
- Time Domain Analysis involves viewing the signal
as a series of voltages as a function of time,
x(0), x(t1), x(t2),...,x(tn-1) - e.g., skin conductance response, event-related
potential - Relevant dependent variables
- latency of a particular response
- amplitude of that response within the time window
- More about time domain in 2 weeks
26Time Domain Vs Frequency Domain Analysis
- Frequency Domain Analysis involves characterizing
the signal in terms of its component frequencies - Assumes periodic signals
- Periodic signals (definition)
- Repetitive
- Repetitive
- Repetition occurs at uniformly spaced intervals
of time - Periodic signal is assumed to persist from
infinite past to infinite future
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28Fourier Series Representation
- If a signal is periodic, the signal can be
expressed as the sum of sine and cosine waves of
different amplitudes and frequencies - This is known as the Fourier Series
Representation of a signal
29Fourier Series Representation
- Pragmatic Details
- Lowest Fundamental Frequency is 1/T
- Tperiod sampled by the N samples
- Resolution is 1/T
- Phase and Power
- There exist a phase component and an amplitude
component to the Fourier series representation - Using both, it is possible to completely
reconstruct the waveform. - Psychophysiologist usually only interested in
amplitude component
30Sine wave
9.75 Hz wave with noise added
Noise Only lt 20 Hz
Mixture of 3 waveforms
Time Domain Frequency Domain
31Averaging Multiple Epochs improves ability to
resolve signal
Note noise is twice amplitude of the signal
32Lingering details
- In absence of phase information, it is impossible
to reconstruct the original signal - Infinite number of signals that could produce the
same amplitude or power spectrum - Spectra most often derived via a Fast Fourier
transform (FFT) a fourier transform of a
discretely sampled band-limited signal with a
power of 2 samples - Windowing the Hamming or Hanning Taper
33Hanning Window Overlapping epochs by 75 will
reduce effects of smearing
34Pragmatic concerns with sample rate
- Sample fast enough so no frequencies exceed
Nyquist - Sample a long enough epoch so that lowest
frequency will go through at least one period - Sample a periodic signal
- if subject is engaging in task, make sure that
subject is engaged during entire epoch
35Lateralization of cognitive specialization
- Damage to left hemisphere interferes with
language processing math/analytic tasks - Damage to right hemisphere interferes with
spatial relations gestalt, synthetic tasks - Galin Ornstein (1972)
- Ps perform 4 tasks (verbal, spatial vs. mental,
motor) - Verbal write letter mentally compose a letter
- Spatial 2-dimensional geometric pattern to
memorize construct pattern with colored blocks
sectioned figure must id what it is - EEG from T3/4 and P3/4
- Analyzed power in 1-35 Hz
- Greater right than left activity (inverse)
occurred in spatial - Greater left than right activity occurred in
verbal
36Concerns with Galin Ornstein (1972)
- Use of power between 1-35 Hz
- Were verbal spatial tasks matched on
difficulty? - Davidson, Chapman, Chapman, Henriques (1990)
used verbal spatial tasks matched on difficulty
(mean, SD, alpha) dot localization word
finding - Found significant task x hemisphere effects for
delta, theta, alpha, and beta - Strongest effects for alpha in central parietal
regions - Less power in most activated hemisphere
- No functional significance of different bands
37Frontal lateralization of emotion
- Lesion findings
- LH damage -- depression
- RH damage -- mania
- EEG studies
- Trait (40 studies)
- State (25 studies)
38Left Hypofrontality in Depression
Henriques Davidson (1991) see also, Allen et
al. (1993), Gotlib et al. (1998) Henriques
Davidson (1990) Reid Duke and Allen (1998)
Shaffer et al (1983)
39Individual Subjects Data
40From Tomarken et al. (1992) bars refer to alpha
power Ss with more left frontal activity
(inverse of alpha) had greater PA and a trend to
lesser NA groups were top of bottom quartiles
on asymmetry over 2 sessions.
41From Tomarken Davidson (1994) -- Mean
standardized Marlowe-Crowne Social Desirability
Scale, State-Trait Anxiety Inventory (STAI)
Trait, and Beck Depression (BDI) scores for the
left midfrontal ( n 12) and right midfrontal (
n 13) groups. Groups were top of bottom
quartiles on asymmetry over 2 sessions.
42The Behavioral Approach System
- sensitive to signals of
- conditioned reward
- nonpunishment
- escape from punishment
- Results in
- driven pursuit of appetitive stimuli
- appetitive or incentive motivation
- Decreased propensity for depression (Depue
Iacono, 1989 Fowles 1988)
43Methods for BAS/BIS Study
- Carver White (1994) BAS/BIS scales
- BIS
- I worry about making mistakes.
- I have very few fears compared to my friends.
- BAS
- When good things happen to me, it affects me
strongly. - I go out of my way to get things I want.
- I crave excitement and new sensations.
- Resting EEG (4 min)
44a
a
b
c
Bars with different superscripts are different at
p lt .05.
45Results of BAS/BIS StudyHarmon-Jones Allen
(1997)
- BAS related to relative left frontal activity
- r .38 , p lt .05
- Even when total frontal alpha power was entered
first in a regression analysis ?R2 .11 , p lt
.05, beta .35 - BIS did not relate to frontal asymmetry
- BAS results replicated in Sutton Davidson (1997)
46State Changes
- Infants
- Stanger/Mother paradigm (Fox Davidson, 1986)
- Sucrose Vs water (Fox Davidson, 1988)
- Films of facial expressions (Jones Fox, 1992
Davidson Fox, 1982) -
47Fox Davidson (1988)
- Mean EEG Power for the 312 Hz Frequency Band for
the Scalp Leads F3 and F4 (Referenced to Cz) in
10-Month-Old Infants Who Displayed Smiles With or
Without Orbicularis Oculi
48Field et al. (1995)
- Frontal EEG asymmetry scores for infants of
depressed and nondepressed women and frontal EEG
asymmetry scores for depressed and nondepressed
mothers
49Models of Asymmetrical Frontal Activity
- Motivational Model
- Left frontal approach motivation
- Right frontal withdrawal motivation
- Valence Model
- Left frontal positive affect
- Right frontal negative affect
50Predictions for the two models
- Converge for most emotions
- Positive emotions (interest, joy) are associated
with approach motivation - Negative emotions (fear, disgust) are associated
with withdrawal motivation - But what about ANGER?
51Anger as Negative
- Often occurs in response to negatively evaluated
situations - Often evaluated as a negative feeling state
52Anger as Approach
- Evokes approach action tendencies
- Darwin (1965), Plutchik (1980), Izard (1991)
- Anger may underlie offensive aggression
- Blanchard Blanchard (1984), Lagerspetz (1969),
Moyer (1976)
53Offensive Aggression angry
Defensive Aggression fearful
54Anger as Approach
- Trait anger relates to trait behavioral approach
sensitivity - at simple correlation level in simultaneous
regression controlling for negative affect and
behavioral inhibition - BAS example item
- I crave excitement and new sensations.
- It would excite me to win a contest.
- Trait anger example items
- When frustrated, I let my irritation show
- Some of my friends think I am a hothead.
55Anger as Approach
- Predicting trait anger
- Predictor partial r p
- BAS .26 .001
- BIS .08 .35
- NA .35 .001
- from Harmon-Jones (in press, Study 1)
56Anger as Approach
- Predicting physical aggression
- Predictor partial r p
- BAS .46 .003
- BIS -.53 .001
- NA .60 .001
- from Harmon-Jones (in press, Study 2)
57Competing Predictions
- If frontal asymmetry reflects valence of emotion,
then anger should relate to increased right
frontal activity, because anger is a negative
emotion - If frontal asymmetry reflects motivational
direction of emotion, then anger should relate to
increased left frontal activity, because anger
evokes approach tendencies
58Relationship of trait anger and resting frontal
asymmetry
- Assessed relationship between resting frontal EEG
over 8 min trait anger - Buss Perry (1992) trait questionnaire
- When frustrated, I let my irritation show.
- Trait anger related to increased left frontal
activity and decreased right frontal activity - In 2 samples
- Harmon-Jones Allen (1998, JPSP)
- Middle school children
- Harmon-Jones (2002, under review)
- College students
59Anger and Asymmetry Correlations
Areas in deep red reflect significant positive
correlations. Areas in blue reflect n.s. negative
correlations.
60- Controlling for positive affect and negative
affect, as assessed by PANAS, did not alter
magnitude of anger asymmetry correlation.
61Addressing an Alternative Explanation for Trait
Anger Research
- Alternative explanation persons high in trait
anger regard anger as a positive feeling - Created Attitudes toward Anger individual
differences questionnaire I like how it feels
when I am mad. - Trait anger related to relative left frontal
activity but attitude toward anger (ATA) did not. - ATA did not mediate the anger-asymmetry
relationship.
Harmon-Jones (under review)
62State Anger and Frontal Asymmetry
- Would situationally-induced anger relate to
relative left frontal activity?
63MethodHarmon-Jones Sigelman (2001, JPSP)
- Told they would participant in two perception
tasks person perception taste perception - Person perception task insult manipulation
- participant writes essay on important social
issue another ostensible participant gives
written feedback on essay - Feedback is neutral or insulting
64Neutral Feedback
- Boring Thought-Provoking
- 1 2 3 4 5 6 7 8
9 -
- Other P gave moderately positive ratings on
intelligent, thought-provoking, friendly,
logical, respectable, rational. - Under additional comments
- I can understand why a person would think like
this.
65Anger-Inducing Feedback
- Boring Thought-Provoking
- 1 2 3 4 5 6 7 8
9 - Other P gave negative ratings on intelligent,
thought-provoking, friendly, logical,
respectable, rational. - Under additional comments
- I cant believe an educated person would think
like this. I hope this person learns something
while at UW.
66- Record EEG immediately after feedback
- Taste perception task aggression measure
- participant selects beverage for other
participant, so that experimenter can remain
blind to type of beverage. - 6 beverages range from pleasant-tasting
(sweetened water) to unpleasant-tasting (water
with hot sauce)
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68Harmon-Jones Sigelman (2001, JPSP)
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