Davidson, R.
(1992)
Anterior
cerebral asymmetry and the nature of Emotion
Brain and
Cognition, 20, 125-151
Cf
cognition Emotion is observable by others and often accompanied by frank
biological changes that are readily perceived by the individual concerned.
Theory that motivates the research - role of cerebral
hemispheres in emotional processing
p 126 '
approach and withdrawal are fundamental motivational dimensions which may be
found at any level of phylogeny where behaviour itself is present.
Damage to
left frontal p127 'results in behaviour an experience which might best be
characterised as a deficit in approach. (KRO ? Right hemisphere modulation of
emotional experience predominates)
'during
the experimental arousal of withdrawal -reared emotional sates ( e.g. Fear and
disgust) the right frontal and anterior temporal regions are selectively
activated. In addition, subjects with baseline tonic activation in these
regions show a propensity to respond with accentuated withdrawal related
negative affect to appropriate emotional elicitors'
Anterior
activation asymmetry (?kro as a trait) functions as a diathesis which
predisposes an individual to respond with predominately positive or negative
affect, given an appropriate emotion elicitor.
Methods description
p 130 time
resolution
sub zero
to several minutes ' many of the core phenomena of emotion are brief and therefore require measures that have a
very fast time resolution'. 'periods of peak emotional intensity are
unpredictable' 'It is also important to be able to record physiological
activity over much long time intervals. This is needed when subjects are
presented with affect elicitors that last several minutes, requiring physiology
to be integrated over the entire period of the eliciting stimulus'
Non
invasive less like that PET, fMRI, to cause emotion related states such as
anxiety
Can
synchronise with behavioural signs
P 152 '
The principal measure extracted from the EEG in the studies I present in this
article is power in the alpha band....... A wealth of evidence indicates that
power in this frequency band is inversely related to activation in adults
(e.g. Shagass, 1972)....... Our
measures. Of band power are computed from the output of the FFT which decomposes
the brain activity into its underlying sine wave components ( KRO why not
cosine as well).
From
another Davidson article and based on
Schaffer, C.E., Davidson, R.J., and Saron, C. (1983) Frontal and
parietal asymmetries in depressed and non-depressed subjects, Biological
Psychiatry, 18, 753-762
Resting
EEG was recorded for both eyes open and eyes closed for 30 sec periods prior to
the administration of various cognitive and affective tasks. Alpha activity
from left and right frontal and left and right parietal regions (F3, F4,P3, P4)
referenced to a common vertex (Cz) was extracted from all artefact-free epochs.
The results revealed no group differences. For either frontal or parietal EEG
during the eyes open base-line period. However for the eyes-closed resting
period, a significant (0.5) Group effect was obtained on a measure of frontal
alpha asymmetry (R-L/R+L. Alpha power; higher numbers on this index reflect
greater relative left-sided activation). Depressed subjects show greater
relative right-frontal activation than do non-depressed subjects
Research
on anterior asymmetries associated with the phasic arousal of emotion
IDs in
baseline asymmetry and affective reactivity
Anterior asymmetries during the experimental arousal of
approach and withdrawal related emotion
p 132 '
adult subjects were exposed to short film clips designed to induce
approach-related positive emotion and withdrawal-related negative emotion'
' when
two or more emotions are compared for their effects on either physiological or
behavioural dependent variables the intensity of the elicited emotion must be
comparable,. If the emotions differ in intensity, then any differences found between them could be
attributed to intensity per se , rather than to the qualitative nature of the
emotions aroused.'
-matched
intensity determined by self report!
FACs
scoring of concurrent video recording used to termite onset of happy and
disgust facial expressions
EEG
during the periods was Fourier transformed and power in different frequency
bands was calculated. p 133 'Based upon on the theory evidence reviewed above,
we hypothesised that the disgust periods would be associated with greater right
sided anterior activation that would happy periods and that the happy periods
would be associated with greater left- sided activation than would disgust
periods.
Davidson
takes the mean log-transformed alpha power and with this transformation ' more
negative numbers indicate less alpha power. The negative numbers are a function
of the log transformation. Lower numbers
( i.e. more negative ) are associated with increased activation' (KRO
???? implies that less alpha power is associated with increased
activation) The results p 133-134 '
disgust is associated with less alpha power I.e. more activation, in the right
frontal lead than is happiness, while happiness is associated with less alpha
power in the left frontal lead than is disgust. ' Also found at temporal electrodes but not at
the parietal.
For
asymmetry index p 134 ' log right minus log left alpha power. Higher numbers on
this scale denote greater relative left sided activation' all subjects showed a
lowers ore on is index during the disgust rather than happy phase. 'We also
found at there were large IDs among individuals in their average asymmetry
scores. ( across emotion conditions ). The difference between happy and disgust
conditions appears to be superimposed upon subjects' basal levels of
asymmetry.' When comparisons were made
without preselects on of EEG based on facial expression the means were in the
expected direction but a statistically
significant difference could not be
confirmed for the asymmetry measures.
Studies in infants: Important because it compares
spontaneous and voluntary smiling
Used
taste to investigate whether asymmetries are present at birth - yes.
Spontaneous
- both zygomatic and orbicularis oculi - felt happiness (Duchenne)
Voluntary
zygomatic
Darwin
(1872) suggested that the duration of each smile type differed. Ie spontaneous
longer. Confirmed by Ekman, Davidson
& Frieson, 1990 self report of emotion and relative activation of the
appropriate facial muscles was correlated.
Facial
behaviour coded by EM FACs system (streamlined version of the FACs)
Stimulus
- approach of either a stranger or the mother. Results p 138 'We specifically predicted that smiles with
orbicularis activity would be accompanied by more relative left - sided frontal
activation than the other smile. .....
Data strongly supported this hypothesis.'
more left frontal activation with spontaneous smiling has been confirmed in adults. (Ekman,
Davidson & Friesen, 1990)
Individual differences in anterior symmetry: A neural
substrate for affective style.
Davidson
sees any response to emotional stimuli as
p 139 ' superimposed upon large individual differences in the overall magnitude
and direction of asymmetry. In other research, we have found that a subject's
overall (across task) EEG asymmetry during task performance is highly correlated with their asymmetry
during a resting baseline. ( e.g. Davidson, Taylor and Sharon, 1979) and that anterior asymmetries during resting
baselines are stable over time ( Tomarken et al, 1990). With test- retreat
correlations ranging between 0.66 and 0.73 for different measures of anterior
activation asymmetry
Scaffer,
Davidson & Saron, 1983 -depressed subjects had less left frontal activation
than the non depressed subjects. p 140 '
An important question concerning these findings with depressives is the degree
to which they are state - dependent. Is the decrease in left frontal activation
a marker of the state of depression or
is a more trait like characteristic which marks an individual' s
vulnerability to depression'
Results
from an experiment to investigate that question
' The results indicate that the decreased left anterior activation which
is characteristic of depression remains. Even when the depression is remitted.
In turn, these findings suggest that 'depressogenic' asymmetry patterns may be
a state
-independent marker that indexes risk for depression.'
In a
further study p 141 ' We hypothesised that subjects with greater right sided
frontal activation at rest would report more intense negative affect in spouse
to film clips signed to elicit fear and disgust. ...... W found that measures
of frontal activations asymmetry recorded prior to the presentation of the film
clips accounted fro a significant variance in subjects' self-reports of negative affect in response to the clips.
Subjects with greater relative right-sided frontal activation reported. More
intense negative affect to the clips.'
