Adolescent brain L5

• Puberty


  Involves many changes including hormonal changes
• Males


  • 30-40% change throughout the day in testosterone
• Females


  • 30-40% change throughout the month in Estrogen
• How puberty starts


  1. HPG axis (hypothalamic-pituitary-gonadal axis)

  2. Secretion of chemical messages from hypothalamus

  3. Signal to pituitary gland to regulate/activate growth hormone levels

  4. Release FSH + LH to trigger release of sex hormones
• Gonadarche


  Early changes involved in puberty
• Gonadarche


  • Onset is a little earlier for females than males
  • Order of changes is relatively the same between individuals
  • Changes are different between girls and boys, making research difficult
• Adrenarche


  • Typically begins around 5-7 years of age
  • Starts when DHEAS and DHEA begins to increase in secretion by the adrenal glands
• It is debated whether adrenarche is counted as part of puberty or not
• DHEA has similar levels of increase in both males and females during adrenarche but then become different during gonadarche
• Puberty (HPG axis)


  Affects the stress system (HPA axis)
• Effects of puberty on brain development

  • Animal literature showing effects of pubertal hormones on brain structure and behavior
  • Heightened neural activity in puberty
  • Pubertal hormones are related to brain growth
  • Apparent differences in brain maturation between males and females
  • Sex-specific differences in mental health pathology
• Animal studies have shown that number of dendritic spines is related to hormones and can be increased with hormonal increases (testosterone and estradiol)
• Functional changes in the brain can be related to testosterone, estrogen and also DHEAS which all bind to receptors in the brain and can affect the density of these receptors throughout the brain
• Organizational hormone effects


  Can happen in sensitive periods in development and have permanent effects on brain structure/brain functioning (wire the brain differently)
• Activational hormone effects


  On a daily basis if you gave a adult a shot of testosterone you would see a change in behavior but if you didn't give the shot, there would be no change in behavior (momentarily and short term effects)
• Models highlighting organizational and activational effects are highly oversimplified as it is often a combination of these effects
• Increased sensitivity of the brain's reward system (nucleus accumbens) during adolescence
• Testosterone


  Moderates the effects of nucleus accumbens activity in adolescence
• Not all brain regions mature at the same time. Generally, visual regions develop early whilst fronto and temporal regions develop late
• There is some kind of pubertal growth spurt going on in the brain structure at around 15yrs
• Testosterone


  Related to development of nucleus accumbens in boys but not in girls
• The connectivity in the nucleus accumbens increases in change speed (how fast it develops) in adolescence - it develops faster during adolescence
• Brains overall size is a little larger in males vs females but we don't see this difference in developmental trajectory (there is no evidence that they develop size at different times)
• The diagnosis for any mental disorder peaks in for boys at around 7-8yrs old whilst for girls the peak is around 15yrs old (during puberty)