Davidson 2004

Davidson, R.J. (2004)

What does the prefrontal cortex "do" in affact: perspectives on frontal EEG asymmetry research

Biological Psychology, 67, 157-182, 219-233

Historical appraisal alpha asymmetry and emotion

1979 EEG asymmetry first reported, at that time p 220 ' research on CNC substrates of emotional processes largely restricted to non-human species with focus on the subcortical'

But p222 we now know that  ' Emotion and motivation are instantiated in complex circuitry involving both cortical and sub cortical components'

Work presented up to 2004 has evolved with little connection to this  recent core neuroscience on structure and function - D argues that this state of affairs must change therefore  D  specifies some questions.

What is the PFC doing in emotion?

some facts to bear in mind

•   PFC is heterogenous (anatomically and functionally) and part of a larger network

•   Based on cell recordings-  animal studies ( 2 macaque monkeys) ' tasks that include a response component will be more likely to show affect related PFC activation asymmetry in the dorsal lateral regions and it is activity in these regions that is most likely to be reflected in scalp recorded brain signals'

•   Recent studies ' have also identified a ventromedial region of PFC that shows robust asymmetries during response inhibition tasks' ( also patient data with damage on right side I.e. r. VmQPFC ? Particularly susceptible to punishment)

p223

•   Suggestions that regions of the l.PFC play an important role in inhibiting the amygdala -' strong inverse relations between activation in the l.v.m.PFC and amygdala when subjects are asked to voluntarily down regulate  their negative affect. The findings collectively imply that what the PFC is doing in emotion is clearly NOT mediating emotional responses but rather moderating patterns of activity in other parts that control the primary emotional response'

'Unfortunately though, little work at the human level has begun to parse emotion in a fashion that derives from and honours the distinctions that are made at a neural level'

' For certain types of emotional processes the presence of a particular pattern of functional prefrontal asymmetry may be necessary but not sufficient for the emotional state in question, or may simply be contributory'

KRO - moderation ? emotional tone

Self report of conscious mood - a summary index of a range of complex emotional processes

IDs in baseline activations

p225 ' individuals with higher levels of l.sided PQF activity do indeed have a more positive profile of peripheral biological indicators' there is evidence of well being , the ability to cope with a negative event (resilience).

Reward is a factor that has been manipulated

P 225  ' it is during the period in anticipation of reward that the most pronounced l. Frontal activation is observed'

p226

Damasio v.m.PFC ' crucial substrate for affect guided decision making' - ? are there functional asymmetries Note Davidson has argued that there are functional asymmetries in dorsal prefrontal

P227

SES and asymmetry

Tomarken ( this issue) ' relations between SES and PF asymmetry in adolescence. The lower the SES, the greater the relative right-sided prefrontal activity'

Empirical and methodological issues

p221 ' the PF sector most directly associated with emotion is the sector that is least likely to be reflected in scalp-recorded brain electrical signals' hence the importance of a neurally informed strategy'  KRO - from clinical practice  we know that it would be naive to expect more than a generalised view of the activation patterns that underlying each electrode

Harmon-Jones ( this issue) Variations in levels of anger lead to increased left-frontal activation and ultimately approach behaviours. Davidson's caveat -' but only if there are response options that allow the individual to overcome whatever is thwarting the goal'

p227 articles ' establish prefrontal EEG asymmetry measures as reflecting, at least in part, trait like variations in brain function that appear to predict interesting and important features of affective style'

Reference electrode some studies report that method robust to location, some do not. Important to take into account that EEG recordings reflect the potential difference between two locations and there is no electrically neutral location anywhere on the body

other frequency bands

Oakes et al, 2004 ' although alpha shows the predicted inverse relation with metabolism ' ' the frequency band most consistently and strongly associated with glucose metabolism was gamma'

Pizzagalli refs for comparisons between frequency bands

Davidson (1992)

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.'