What is puberty characterised by?
3 endocrine events:
1) Adrenarche
2) Gonadarche
3) Activation of growth axis
What is adrenarche characterised by?
- Between 6-9 in females, a year later in males
- Activation of HPA axis for adrenal production (zona reticularis)
- Adrenal androgens (DHEA and DHEAS) increase and continue to rise throughout early adulthood before declining
- Contributes to development of secondary sexual characteristics + changes in sweat glands
What is gonadarche characterised by?
- Between 8-14 in females, 9-15 in males
- Inhibited by reactivation of HPG axis (pulsatile secretion of GnRH from hypothalamus during sleep)
- Stimulates anterior pituitary production LH + FSH > gonadal maturation
= Secretion gonadal steroid oestrogen + testosterone
What is the activation of growth axis characterised by?
- GH secreted from pituitary during sleep
= linear growth spurt @ 12 in girls, 14 in boys - Children in adverse enviro = hyperactive HPA axis + reduces GH secretion
What are the hormonal effects of puberty on brain + behaviour?
- Trigger second period of structural reorganisation + plasticity in brain
- Facilitation of reproductive behaviours (mainly via hypothalamus)
- Reorganisation of sensory + association regions (visual cortex, amygdala, hippocampus)
- Motivation + reward-related behaviour (nucleus accumbens, dopaminergic pathways to prefrontal cortex )
- Increased biobehavioural reactivity to stress exposure (HPA axis undergoes maturational increase in baseline activity + sensitivity)
What are the chronic effects of stress on brain and behaviour?
- HPA dysfunction in depression, anxiety + psychosis
- Traumatic stress = dysregulation of stress responses (HPA axis, immune response, catecholamines)
- Early life stress = suppressed immune response + elevated inflam markers + increased risk metabolic syndrome
Summarise the cortisol feedback mechanism
CRF > ACTH > Cortisol
What white matter structural changes take place in adolescent brain development?
- Steady linear increase in white matter vol
- Due to progressive age-related axonal myelination > greater connectivity + integration
- Males show steeper age-related increase
What grey matter structural changes take place in adolescent brain development?
- Inverted U shape pattern
- Pre-pubertal increase followed by post-pubertal loss
- Motor + sensory systems mature earlier
- Synaptic pruning
What causes non-linear changes in grey matter volume?
- Rarely used connections eliminated, making brain more efficient
- Neuroplasticity = structural changed due to exposure to + and - enviro stimuli
What cognitive development takes place during adolescence?
- Synaptic pruning + axonal myelination = changes in cog functioning
- Maturation of prefrontal cortex = greater control + coordination of thoughts + behaviour, metacogntion, LT planning + self evaluation
- Impaired connectivity between regions of prefrontal cortex + areas of limbic system
What causes heightened risk taking in adolescence?
Due to interaction between 2 brain networks
1) Prefrontal cognitive-control network (executive functions) matures gradually
2) Subcortical motivational drive network rapidly remodelled in early adolescence by hormonal changes
Temporal disjunction between maturation of socioemotional system + maturation of cognitive control system = risk taking
Why do so many psychiatric disorders start in adolescence?
- Regulatory systems gradually brought under control of executive functions
= considerable opportunities for development suboptimal patterns - Excessive down reg mood + motivation = depression
- Inadequate control arousal = impulse control problems
How do so many psychiatric illnesses start in adolescence?
- Genetic anomalies
- Biological factors
- Early development experiences that influence synaptic pruning etc
- Stress exposure (interaction between HPA axis + glucocorticoids)
What are the symptoms of unipolar depressive disorder in adolescence?
- Increased risk anxiety, disruptive behaviour, substance misuse
- Persistent low mood
- Anhedonia
- Fatigue
- Sleep
- Appetite disturbance
- Poor concentration
- Agitation
- Guilt
What is the impact of inherited & environmental factors on shaping biological mechanisms?
- Increased activity in circuit that connects amygdala, hippocampus + PFC & is linked to HPA stress-system
- Reduced activity in circuit connecting striatum to PFC + ventral dopamine based systems (reward circuit)
What are the key characteristics of schizophrenia in adolescence?
- Average age onset 15-25
- Postive symptoms = delusions + hallucinations
- Negative symptoms = social withdrawal, flat affect, alogia, avolition
- Cognitive symptoms = impaired attention + executive functions
What factors contribute to onset of schizophrenia in adolescence?
- Genetic
- Early exposure to aversive life events + stressors
- Environmental
- Adverse living conditions
