Pre-Adult Brain Development (Biological)

Brain development

Structures

Structure of brain is hierarchal -> primitive structures develop first, more advanced structures develop later and continue through adolescence

Limbic system:

  • Develops through childhood and adolescence
  • Structures including amygdala which connects to the ventral striatum and nucleus accumbens
  • Processes emotional experiences and regulates emotions

Cerebral cortex:

  • Thin covering of the brain, where thinking takes place
  • Divided into number of cortexes
  • Frontal cortexes controls higher cognitive functions (abstract thinking) and problem solving/decision making
  • Auditory-visual cortex -> processing of sensory information
  • Motor cortex -> movement-related information
  • Extensive development in early years but reaches full maturity in late adolescence

Developmental processes

Synaptogenesis:

  • Born with all neurons we need, but synapses develop in childhood and beyond
  • Synaptogenesis is process of new neurons forming
  • Develop when axons and dendrites grow towards each other to form networks
  • Contributes to greater complexity of the brain
  • More synapses = more neurotransmitter activity

Myelination:

  • Brain growth from birth to two years old grows form 25% to 75% of adult brain size
  • Myelin is a fatty substance that insulates neurons
  • Allows conduction of electricity

Synaptic pruning:

  • Creates organisation in the brain
  • Period of synaptic loss to fine tune brain structure
  • Inactive synapses are ones to be pruned
  • Allows areas to become specialised for certain functions ( e.g. auditory, visual, sensory, motor, etc)
  • Surviving neurons become myelinated

Risk-taking and the brain

  • Adolescence is synonymous with risk-taking in the minds of many parents, teachers an politicians (e.g. binge drinking, drug taking, reckless driving, unprotected sex)
  • Some reality to stereotypes -> e.g. mortality rate and unintentional injuries increase from childhood to adolescence (Western)
  • Main cause for death/disability in adolescence is preventable (accidents/suicides)

Dual-systems theory:

  • Steinberg (2008) -> dual-systems theory: risk-taking in adolescence is directed by the interaction of two brain systems that mature at different times
  • Ventral striatum (VS): emotion-regulating system that matures relatively early in adolescence in response to changes in the ventral striatum
  • Changes due to increased dopamine
  • VS includes nucleus accumbens (NA) which is key in brain's reward system -> sensation-seeking/addiction
  • VS has greater sensitivity in adolescence
  • Johnston (2006) -> changes in VS matched increase in arrests for criminal behaviour, peaks mid-late adolescence
  • Peak female 16, male 19
  • Prefrontal cortex (PFC) -> slower to develop
  • Cognitive control system directed by PFC, linked with planning, decision-making, response inhibition, goal-directed behaviour, ability to assess risk
  • Synaptic pruning -> doesn't fully mature until young adulthood
  • Not able to exert executive control over first system that rewards sensation-seeking behaviours associated with taking risks
  • Imbalance between systems only during adolescence
  • Adolescent behaviour more impulsive than child/adulthood

Research study:

  • Meyer and Bucci (2016) -> lab experiment to mimic system imbalance in rats
  • Decreased PFC and increased NA
  • Rats took twice as long as control group to learn to inhibit response to expected reward
  • Not normal behaviour but matched behaviour of adolescent rats

Barkley-Levenson and Galvan (2014) on the Adolescent brain

Background and aims

  • Galvan (2013) showed heightened sensitivity to rewards -> linked with increased response of VS when adolescent anticipates or receives or receives expected/unexpected rewards
  • Unclear if due to genuine phenomenon or extraneous variables -> use of money as a reward -> people value money more than others
  • Barkley-Levenson and Galvan defined subjective value (SV) as 'the value that an individual places on a stimulus'
  • Batra (2013) -> ventromedial prefrontal cortex (PFC) and VS together form brain's valuation system
  • How brain represents SV measured by expected value (EV). Defined as 'sum of all the possible outcomes of a choice multiplied by their probabilities'

Aims:

  • Adolescents would be more sensitive than adults to increased EV
    Adolescents would show greater VS activation as EV increased, compared to adults
  • Adolescents would still show a heightened VS response even after matching with adults on number of gambles accepted

Method

Lab-based quasi experiment. IV was whether participant was adult/adolescent. DV were number of gambles in a 'spinner' game accepted by participant and activity in ventral striatum of brain

Sample:

  • 19 adults 25-30 yrs (8m, 11f) and 22 adolescents 13-17 yrs (11m, 11f). All right-handed
  • Self-selected -> advertised posters/online
  • Used previous UCLA participants
  • All healthy

Apparatus:

  • fMRI scans using a 3-Tesla Trio MRI machine
  • 140 functional, 2 structural images taken per p

Procedure

Intake session:

  • Adult ps gave informed consent, under 18s -> parents gave informed consent
  • Ps given details of monthly allowance and where it came from
  • Average for adults $467.11, average for adolescents $52.50
  • End of session, each given $20 as playing money -> chance to double or nothing (gave effect of ownership)

Each participant visited the lab on two occasions for an intake session and again one week later for fMRI

fMRI session:

  • Gambling task -> spinner
  • Ps shown on-screen spinner split in two between $5 and $20. One value gain, other lose
  • Gain and loss countered for ps
  • Trials: 192 per p. 24 runs had only gain, 24 would be loss, 48 mixed trials -> would show risk-taking behaviour
  • EV mixed value: -$7.50 - +$7.50
  • EV gain only: +$6 - +$19
  • EV loss only: -$6 - -$19
  • Task was to decide on which trial whether or not they were prepared to gamble their money
  • Money added or removed at end of run for participation
  • Ps trained in task before scan

Results

First hypothesis:

  • Increasing EV made acceptance of gamble more likely. Greater in adolescents
  • Disposable income had no effect on link with EV and gamble acceptance
  • Researchers analysed gain-only and loss-only trials -> not risky because ps knew outcomes
  • Gamble acceptance didn't change for adults or adolescents
  • Adolescents behave as adults when no risk involved

Second hypothesis:

  • fMRI scans showed as EV increased, increased activation in superior medial PFC
  • Decreased activation accompanying increased EV in other brain areas such as amygdala and hippocampus
  • Adolescents show greater activation to increased EV in left VS than adults

Third hypothesis:

  • Researchers matched two groups on acceptance behaviour by analysing data from ps with high gambling acceptance (>80%) on high EV trials
  • Found that difference remained

Conclusions

  • Adolescent brain uniquely heightened sensitivity to rewards
  • Valuation system in medial PFC and adjacent areas
  • VS important in valuation in adolescents
  • Hyperactivation of VS in adolescents

Strategies to reduce risk-taking behaviour using knowledge of brain development

Nurse visitation programmes (NVP)

  • Severe stress early in life can increase likelihood of risk-taking behaviour in adolescence
  • Early stressful experiences can disrupt synaptogenesis/synaptic pruning
  • Associated hormones can damage prefrontal cortex, limiting influence on VS
  • Nurse visitation programme (NVP) targets men/women expecting a baby and high risk of mistreating it
  • Reducing stress

Usefulness:

  • Preventing mistreatment of child is beneficial, avoids risk of damaging brain structure and processes (e.g. synaptogenesis)
  • Intervention encourages parents to provide better nurturing care for child
  • Care continues into adolescence and breaks links with development of impulsivity and ultimately risk-taking behaviours

Effectiveness:

  • Izzo (2005) structured interview with mothers 15 years after NVP. Able to cope better than mothers not on NVP
  • Interviewed children -> ran away from home less, were arrested less often, had fewer sexual partners, smoked less, had fewer alcohol/drug related behavioural problems
  • No effect on suspensions from school, disruption in school, 'major delinquent acts'

Practicalities:

  • Results included mothers that has pre-birth visit but none else, later outcomes not as positive than ps with full interaction

Graduated driver programmes

Graduated driver programmes (GDP) commonly used in US to reduce incidence in inexperienced driver's first 1000 miles

Driving and the pre-adult brain:

  • Delay of maturation of brain governed by VS results in underdevelopment of cognitive skills crucial to driving

Reducing the impact of arousal:

  • High arousal caused by driving and with friends
  • Together can be toxic, interventions devised to prevent combination occurring or reducing impact on behaviour

Stages of GDP:

  • Lower stages -> lower speeds limits, restriction of hands-free mobiles
  • 3 stages -> learner (always supervised), intermediate (only supervised in dark), full privileges (after 18)

Usefulness:

  • Useful restrictions -> limited passengers, friends only allowed in stage 2 with adult present

Effectiveness:

  • Dee (2005) -> GDPs reduced 15-17 years fatalities by 5.6%
  • Romano (2011) -> GDPs reduced speeding-related fatalities in white, African-American and Asian adolescents. Didn't affect Hispanics
  • Risky driving could relate to social and cultural reasons as well as brain development

Practicalities:

  • Pedan (2008) -> most significant element is extended period of supervision in first stage
  • Longer it takes for adolescent to drive unsupervised, less risky driving behaviour

Evaluation

Nature/nurture

Nature:

  • Brain development
  • Synaptic pruning
  • Nature because natural process that occurs during childhood

Nurture:

Freewill/Determinism

Freewill:

  • Barkley-Levenson and Galvan
  • Risk taking behaviour -> choice to behave this way
  • Freewill as individual chooses to act this way

Determinism:

  • Developmental processes
  • Synaptic pruning -> prunes inactive synapses and creates organisation in the brain
  • Deterministic because this will happen regardless of any other factors -> biological

Reductionism/holism

Reductionism:

  • BL and G
  • Risk is due to activation in ventral striatum -> heightened in adolescents
  • Reductionist because it reduces risk-taking behaviours to one factors

Holism:

Individual/situational

Individual:

  • Risk taking and the brain
  • Steinberg (2008) -> dual-systems theory: adolescent risk taking directed by interaction of VS and PFC
  • Individual as this will differ the amount of risk taking behaviour in each adolescent

Situational:

Usefulness

Useful:

Not useful:

Ethical considerations

Not ethical:

  • BL and G
  • Gambling task during fMRI scans in second session
  • Not ethical as may promote gambling in real life

Ethical:

Conducting socially sensitive research

Socially sensitive:

Not socially sensitive:

Psychology as a science

Scientific:

  • BL and G
  • fMRI scanner has set protocol, all ps given identical gambling task
  • Scientific as fMRI protocol is replicable and standardised

Not scientific:

Ethnocentrism

Ethnocentric:

  • BL and G
  • Adolescence seen as individual gaining independence
  • Ethnocentric as the western view of adolescence used (individualist), collectivist cultures may differ results

Not ethnocentric:

Validity

Valid:

  • BL and G
  • Internal validity -> made participants believe they earned $20 during intake session
  • Valid as reduces 'house money effect' so researchers reduced extraneous variables

Not valid:

  • BL and G
  • Ecological validity -> gambling task
  • Lack validity as it resembles few risks take by adolescents and adults in real life

Reliability

Reliable:

  • BL and G
  • fMRI scanner followed established protocol so was conducted and analysed
  • Reliable as established protocol is standardised so makes it replicable -> external

Not reliable:
-

Sampling bias

Bias:

  • BL and G
  • Self-selected sampling using posters and online adverts
  • Biased as may only include certain characteristics -> people who take risks may be more likely to risk signing up

No bias:

  • BL and G
  • Equal male/female ratios in both adult and adolescent participants
  • No bias as reduces gender as extraneous variable