The Electroencephalogram

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The Electroencephalogram
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Electroencephalogram (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

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Utility of EEG

• Relatively noninvasive
• Excellent time resolution

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Sources 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

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Alpha 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

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Alpha
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Alpha 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

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Recording EEG
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Recording EEG
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Electrodes, Electrolyte, Preparation

• Reduce impedance
• Ag-AgCl preferred, tin OK
• Electrolyte ionic, conductive
• Affixing
• Subcutaneous needle electrodes
• Collodion
• EC-2 paste
• Electrocap

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Recording 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

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Recording 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

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Artifacts

• Three sources
• 60-cycle noise
• Muscle artifact
• Eye Movements

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Movement in reference lead
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Chewing
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Vertical eye roll
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Excessive muscle notice saturation of T5
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Talking and moving head
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Yawn
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Eye Closure and reopening
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Blink and Triple blink
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Dealing 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

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High 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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Time 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

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Time 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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Fourier 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

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Fourier 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

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Sine wave
9.75 Hz wave with noise added
Noise Only lt 20 Hz
Mixture of 3 waveforms
Time Domain Frequency Domain
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Averaging Multiple Epochs improves ability to
resolve signal
Note noise is twice amplitude of the signal
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Lingering 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

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Hanning Window Overlapping epochs by 75 will
reduce effects of smearing
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Pragmatic 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

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Lateralization 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

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Concerns 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

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Frontal lateralization of emotion

• Lesion findings
• LH damage -- depression
• RH damage -- mania
• EEG studies
• Trait (40 studies)
• State (25 studies)

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Left 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)
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Individual Subjects Data
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From 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.
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From 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.
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The 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)

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Methods 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)

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a
a
b
c
Bars with different superscripts are different at
p lt .05.
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Results 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)

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State Changes

• Infants
• Stanger/Mother paradigm (Fox Davidson, 1986)
• Sucrose Vs water (Fox Davidson, 1988)
• Films of facial expressions (Jones Fox, 1992
  Davidson Fox, 1982)

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Fox 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

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Field et al. (1995)

• Frontal EEG asymmetry scores for infants of
  depressed and nondepressed women and frontal EEG
  asymmetry scores for depressed and nondepressed
  mothers

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Models of Asymmetrical Frontal Activity

• Motivational Model
• Left frontal approach motivation
• Right frontal withdrawal motivation
• Valence Model
• Left frontal positive affect
• Right frontal negative affect

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Predictions 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?

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Anger as Negative

• Often occurs in response to negatively evaluated
  situations
• Often evaluated as a negative feeling state

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Anger as Approach

• Evokes approach action tendencies
• Darwin (1965), Plutchik (1980), Izard (1991)
• Anger may underlie offensive aggression
• Blanchard Blanchard (1984), Lagerspetz (1969),
  Moyer (1976)

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Offensive Aggression angry
Defensive Aggression fearful
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Anger 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.

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Anger 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)

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Anger 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)

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Competing 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

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Relationship 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

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Anger and Asymmetry Correlations
Areas in deep red reflect significant positive
correlations. Areas in blue reflect n.s. negative
correlations.
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• Controlling for positive affect and negative
  affect, as assessed by PANAS, did not alter
  magnitude of anger asymmetry correlation.

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Addressing 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)
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State Anger and Frontal Asymmetry

• Would situationally-induced anger relate to
  relative left frontal activity?

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MethodHarmon-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

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Neutral 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.

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Anger-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.

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• 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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Harmon-Jones Sigelman (2001, JPSP)
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