Davidson 1988

Davidson, R.D. (1998)

EEG measures of cerebral asymmetry: Conceptual and methodological issues

J. Neuroscience, 39, p 71-89

Comparisons with other neuroscience methods

cf FMRI fewer constraints on task presentation and performance

Critical periods can be flagged ie examine epoch during which facial expression is recorded

Distinctions between Hemisphere specialisation and hemisphere activation

Hemisphere Specialisation

Preparedness to do a task, one hemisphere less accomplished than the other for a particular task

Hemisphere Asymmetries in Activation

p87 ' Activation refers to the degree to which a particular hemisphere is working or engaged'

p 73 ' Activation is typically defined operationally on the basis of the methods used in a particular study to measure this construct'

p 75 ' A hemisphere may become selectively activated as a function of priming'  this means that the task parameters may influence the activation level e.g. The requirement to respond with one hand or another hand (KRO think about cortical activity at a primary level).

' testing must be performed on a sample assumed to be homogenous with respect to individual differences in hemisphere specialisation'

Within subject designs therefore preferred although there can be floor/ceiling effects ie task effect not apparent because baseline measure already at ceiling/ floor

Dissociations between specialisation and activation

'Dissociations between these two aspects is common' ' The hemisphere specialised to process a particular stimulus is not necessarily the one most activated'

p73 ' it is not necessarily the case that differences in activation are paralleled by differences in specialisation'

rostral -caudal differences in hemisphere specialisation and activation

Anterior hemisphere  regions associated with affective processing

Posterior hemisphere regions associated with cognitive processing

I.e. activations are relatively orthogonal

 p76 ' stimuli which differ in affective valence systematically influence activation asymmetries in frontal brain electrical activity in the absence if any simultaneous measures in parietal asymmetry, while tasks which are designed differentially to require verbal versus visual spatial produce changes in parietal and temporal asymmetry in the absence of any modifications in frontal asymmetry processing produce changes in parietal and temporal asymmetry'

This has been checked by the author by taking both frontal and parietal/temporal measures at the same point in time and performing across(rostral-caudal) (e.g. r frontal v r parietal/temporal correlations) p87 ' it makes little sense to talk of a whole hemisphere being activated or specialised for a particular function'

Methodological Issues

1.  metrics of asymmetry

Require the sites to be homologous

Choose the dependent measure; oscillation, ratio/raw

 ( note for ratio measures (R-L)/(R+L) higher ratios are produced by less alpha in the left hemisphere and/or more alpha in the right hemisphere, both of which are associated with more relative left sided activation ( less alpha is taken to be indicative of more activation'

Between group as opposed to within group studies

Small differences ( between hemisphere) may be more significant than overall activations

2. Artefact

Blink & eye movement

EMG What is the spectrum characteristics, how to detect

p78' facial expression , there are reports of asymmetry. ' in our experience most severe in the beta range'  ( but doesn't evidence this) ' the presence of muscle artefact is sufficiently likely in certain scalp locations ( e.g. Temporal leads) as to make meaningful assessment of beta almost impossible' ' in our laboratory, we sample the EEG at 250 Hz and compute power density in a high frequency band (70-80Hz) which does not contain any neurogenic activity and is presumably a function of muscle activity exclusively' ( KRO does that view still hold?)

3 Reference electrode

Laplacian operator for dealing with  questions  that arise concerning the contribution of the reference electrode

Or

Record A1 and A2 with same reference, then average these channels to form a new reference

Mental Capital & Wellbeing

recent shift of emphasis from disorder and dysfunction to well being and positive mental health.

Neurobiology of Wellbeing: a Life-course Perspective

(state of science review SR-X3 for The Foresight Project )

Keverne, E.B.

The developing brain

findings mainly deduced from experimental animal studies

human brain is unique in that much of its growth and development occurs postnatally - up to second decade and beyond the age of 20 in the pre-frontal cortex.

'Puberty has always been a life event producing a challenge for well being, but why is it becoming more problematic?  Can we attribute these problems to failures in early development, or does the protracted development of the brain produce problems in its own right, that are exacerbated by modern lifestyles.?'  'Puberty is undeniably a period of great emotional turmoil when changes in physical phenotype synchronise with reorganisation of the cortex especially those areas of the brain intimately concerned with emotional regulation and forward planning'

'Better nutrition has led to an earlier onset of puberty - is the maturation of the body phenotype becoming out of phase with brain development, or prematurely precipitating brain maturation.?  Did natural selection has shape the evolution of such sensitive periods to optimise successful outcomes ?  Also Hominid behavior has become progressively emancipated from physiological homeostasis and the endocrine biology of our bodies, and primarily determined by the cognitive ability of our large brains. ' Bodies and brains are harmoniously synchronised in most mammals, but in humans the vast expanse of neocortex has emancipated the brain from the body's endocrine signal with cognitive control taking over the decision making process'

Epigenetics, pre and post natal environments

low birth rate can be a factor related to future wellbeing.  

Pivotal role of the placenta at the interface between the adult brain and the developing foetal (parental) brain whilst simultaneously interacting with both.  Co-adaptive selection pressures operate by virtue of two, actively expressing genomes (mother and child)  interacting within one individual 

The post-natal period is particularly sensitive to life's experiences which can include changes in brain development and behavioral phenotype.  eg Harlow and Harlow, maternal deprivation.  Epigenetic effects are induced by differential maternal care.

'Epigenetics requires an understanding of how modifications to the DNA and chromatin bring about long term ( birth to adult) changes and , indeed, transgenerational changes in gene expression without changes to DNA coding structures.'  'There is the possibility that environmental events can have long-lasting effects on genomic function' ' This enables the organism to develop a range of alternative phenotypes according to the environmental cues that it receives early in life' 'Germ-line genetic changes are relatively slow and may be more adapted to the environment of distant ancestors, while epigenetic changes allow animals to become adapted to the current environment in one generation'

There is growing evidence for such epigenetic effects operating in humans

Psychological Wellbeing:  Evidence regarding its causes and consequences

( state of science review SR-X2 for the Foresight Project)

Huppert, F.A.

Psychological well being is about lives going well; it is a combination of feeling good and functioning effectively.  The concept of feeling good incorporates not only positive emotions  of happiness and contentment, but also such emotions as interest, engagement, confidence and affection.  The concept of functioning effectively ( in a psychological sense) involves the development of one's potential, having some control over one's life, having a sense of purpose and experiencing positive relationships.

(  relation with mental health 0- positive mental health (WHO 2001) ' a state of wellbeing in which an individual realises his or her own abilities, can cope with the normal stresses of life, can work productively and fruitfully, and is able to make a contribution to his or her own community  )

evidence for a seminal role of social factors and the early environment

some drivers of well being are involved in ill being ( albeit in an opposite direction) but not all.

+ emotions and cognitive processes.

'Experimental studies using mood induction techniques demonstrate unequivocally that + mood states can enhance attention and other cognitive processes.'

'Findings suggest that + emotions lead to positive cognitions, + behaviours and increased cognitive capability, and that + cognitions, + behaviours and capabilities in turn fuel + emotions' (Fredrickson and Joiner, 2002)

However 'positive emotions are not beneficial for all cognitive processes.  People with negative mood states are better at taking in the details of a situation and people who are sad, anxious or fearful are more conforming and less  likely to break rules.

Fredrickson, B.L. and Joiner, T. (2002) Positive emotions trigger upward spirals toward emotional well-being.  Psychological Science, 13: 172-5.

relevant neuroscience  ( mostly Davidson )

prefrontal cortex - asymmetric activation in relation to positive and negative emotions.  The amount of asymmetry varies with emotional style ( whether an individual tends to feel genrally positive or generally negative).

perfrontal asymmetry stable in adults but not during early childhood.

neurochemical effects

cortisol - well being but not ill being.  Although  there are negative states due to cortical response  these seem to be independant of effects on well being

serotonin.  - well being but not ill being  deficiences lead to absence of well being 

oxytocin - from animal studies it has an effect on mother-infant bonding.  Nasally administered oxytocin leads to a high degree of trust in a risky investment game ( Kosfield et al, 1995)  Therefore some limited eveidence that it may play a role in social bonding.

personality

one of the strongest predictors ( drivers) of emotional style is personality, extraversion with positive and neuroticism with negative emotional style.  

Most widely used measure of positive psychological functioning is Ryff's scales of Psychological Wellbeing.  Recent longidutinal studies using this scale show a much larger effect of extraversion than of neurotocism on sense of well being

Personality account for around 30% of variation in psychological well being.

socioeconomic and demographic

account for just 10% of variation is psychological well being.

the population perspective

US evidence , 17% flourishing whilst 11% languishing in terms of psychological resources .  Targeted approach ( eg the groups at risk ) approach does not seem as effective as achieving minimal shifts across the whole sprectrum,  ie leverage obtained by targetting all the popultion and achieving small change in the majority  cf binge drinking best tackled by targeting the entire population in terms of a drinking culture.