Get documents about "eeg
Document Sample
The Electroencephalogram
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
Utility of EEG
Relatively noninvasive
Excellent time resolution
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
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
Next
Alpha
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
Recording EEG
Recording EEG
Electrodes, Electrolyte, Preparation
Reduce impedance
Ag-AgCl preferred, tin OK
Electrolyte: ionic,
conductive
Affixing
Subcutaneous needle
electrodes
Collodion
EC-2 paste
Electrocap
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
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”
Artifacts
Three sources
60-cycle noise
Muscle artifact
Eye Movements
Movement in reference lead
Chewing
Vertical eye roll
Excessive muscle – notice saturation of T5
Talking and moving head
Yawn
Eye Closure and reopening
Blink and
Triple blink
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
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
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
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
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
Fourier Series Representation
Pragmatic Details
Lowest Fundamental Frequency is 1/T
T=period 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
Sine
wave
9.75 Hz
wave
with noise
added
Noise
Only
< 20 Hz
Mixture of
Time Domain Frequency Domain 3 waveforms
Averaging
Multiple Epochs
improves ability
to resolve signal
Note noise is twice
amplitude of the signal
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
Hanning Window – Overlapping epochs by 75% will reduce
effects of smearing
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
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
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
Frontal lateralization of emotion
Lesion findings
LH damage -- depression
RH damage -- mania
EEG studies
Trait (40+ studies)
State (25 + studies)
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)
Individual
Subjects’ Data
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.
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.
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)
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)
Frontal alpha power as a function
of BAS level and hemisphere
a
3 a
2.5
b c
Alpha
2 Right (F4)
Power
Left (F3)
1.5
1
Low BAS High BAS
Bars with different superscripts are different at p < .05.
Results of BAS/BIS Study
Harmon-Jones & Allen (1997)
BAS related to relative left frontal activity
r = .38 , p < .05
Even when total frontal alpha power was
entered first in a regression analysis: R2 = .11
, p < .05, beta = .35
BIS did not relate to frontal asymmetry
BAS results replicated in Sutton & Davidson
(1997)
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)
Fox & Davidson (1988)
Mean EEG Power for
the 3—12 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
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
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
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?
Anger as Negative
Often occurs in response to negatively
evaluated situations
Often evaluated as a negative feeling state
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)
Offensive Aggression
“angry”
Defensive Aggression
“fearful”
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.”
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)
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)
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
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
Anger and Asymmetry Correlations
Areas in deep red reflect significant positive
correlations. Areas in blue reflect n.s. negative
correlations.
Controlling for positive affect and negative
affect, as assessed by PANAS, did not
alter magnitude of anger & asymmetry
correlation.
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)
State Anger and
Frontal Asymmetry
Would situationally-induced anger relate to
relative left frontal activity?
Method
Harmon-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
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.”
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 can’t believe an educated person would think like
this. I hope this person learns something while at
UW.”
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)
Relative Left Frontal, Anger, &
Aggression as a Function of Condition
0.3
0.1
Standard -0.1 Left Frontal
Scores -0.3 Anger
Aggression
-0.5
-0.7
Neutral Insult
Harmon-Jones & Sigelman (2001, JPSP)
