LECTURE 3 - The developing brain

Peter Huttenlocher’s Contribution:

• studied brain development by analyzing post-mortem brains.

• Found synaptic density increases in childhood and decreases (synaptic pruning) during adolescence and adulthood.

Phineas cage 1948

brain injury in the frontal lobe , he lost left side vision, but gained consciousness right after the incident,

Injury influenced his personality and character, cognitive functions and behaviour

human cerebral cortex development

number of synapses increase and then it starts to decrease gradually in adulthood and adolescence. The brain in this period is very plastic and therefore it adapt very quickly and learn and shapes the brain according to the experiences. Highly flexible and prepared for a variety of potential experiences and learning opportunities.

Synaptogenesis and Pruning

• Synaptogenesis:

  • Formation of synaptic connections begins before birth.

  • Dendrites and synapses multiply rapidly in early development.

• Synaptic Pruning:

  • Excess synapses are eliminated during adolescence.

  • Strengthened synapses = those used regularly (learning).

  • Pruned synapses = unused connections.

The role of experience in the brain development

• there are some critical and sensitive periods when the brain is particularly receptive to experience

• Early development is important but it does not determine development as brain goes through the development process in later stages of life.

• Developmental stage is a heightened plasticity, which allows for more learning but also means that synapses are more easily formed and in response to environmental stimuli.

• In adolescence the brain starts to solidify and certain pathways as part of cognitive maturity, focusing on those for more complex thought processes.

• The simple neural connections from first are way different and complex as the brain ages.

• Different part of brain form stronger connections

• Timing is genetic but early experiences the circuits became strong.

Genes and Experience

• Genes provide the blueprint for brain development.

• Experience fine-tunes neural circuits, especially during sensitive periods.

  • Sensitive periods: Specific times when the brain is highly receptive to environmental stimuli.

  • E.g., sensory processing in infancy, higher cognition in adolescence.

• Example: Children in institutions show reduced brain activity compared to those in foster care or typical homes.

Assessing the emotional brain

the rational part of the brain in the dorsolateral pre-frontal cortex has no direct connections with the emotional brain .

cortical development from 5 to 20 yrs

• cortical development is brain maturation, structural changes,synaptic pruning, refinement of neural circuits, which supports cognitive, emotional and behavioural development.

• Late adolescences brain goes through cortical thinning, which leads to reduction in cortical thinning.

• While grey matter thins, white matter increases, myelination helps improve the speed and efficiEncy of neuronal signals transmission.

Toxic Stress

• Prolonged adverse experiences (toxic stress) can harm brain development.

• Institutionalized children show blunted stress responses (e.g., reduced heart rate change under stress).

• Trauma imprints in emotional brain regions (e.g., the amygdala) and affects self-awareness through the medial prefrontal cortex.

Adolescence and Brain Development

• Brain development continues beyond childhood due to plasticity.

• Changes in grey and white matter:

  • Grey matter increases in childhood, peaks in adolescence, then decreases due to pruning.

  • White matter increases as axons are myelinated (more efficient connections).

  • The prefrontal cortex undergoes the most changes, influencing decision-making and planning.

• Gender differences:

  • Girls show earlier grey matter development in the prefrontal cortex compared to boys.

The Social Brain

• The medial prefrontal cortex is involved in impulse control and executive function.

• Activity decreases from adolescence to adulthood, indicating shifts in cognitive strategies.

Risk-Taking in Adolescence

• Peer influence affects behavior (e.g., adolescent mice consume more alcohol in peer groups). (Logue et. Al, 2014)

• Topics for future research include the effects of:

  • Social media.

  • Substance use.

  • Technology on adolescent brains.

Gender differences in brain development

Grey matter contains cell bodies and connections between sells.

Grey matter develops earlier in females in the pre-frontal cortex, as part of the brain responsible for planning and decision making.

Neuropsychiatric Implications

• Many mental health disorders emerge in adolescence (e.g., depression, schizophrenia, ADHD).

• Brain abnormalities in conditions like depression are observed in the amygdala and hippocampus.

• ADHD: Children with ADHD show atypical neural responses, such as heightened sensitivity to vocal emotions.

When’s does brain plasticity stop developing?

This varies person to person and genetically and environmental factors. However most studies show that it stops at 40 yrs.

Implications for Society

• Education: Adolescents benefit from training in reasoning and numeracy.

• Criminal justice: Brain development insights influence views on adolescent culpability.

• Prevention: Early intervention can mitigate risks of neuropsychiatric disorders.

Brain Plasticity and Lifelong Learning

• Brain plasticity enables learning throughout life.

• Education and cognitive training in adolescence and early adulthood can be impactful.

• The brain stops developing fully around 40 years, though this varies by individual.

ADHD: Neural Abnormalities

ADHD is characterized by inattention, hyperactivity, and impulsivity. Research has identified several structural and functional deviations in the brains of individuals with ADHD:

SYMPTOMS AND EFFECTS OF ADHD

Prefrontal Cortex Dysfunction

The prefrontal cortex, critical for executive functions such as attention, impulse control, and decision-making, often shows reduced activity in ADHD patients. This underactivity is linked to difficulties in maintaining focus and regulating behavior.

2. Delayed Cortical Development

MRI studies reveal delayed cortical maturation, especially in the prefrontal cortex. This delay can persist into adolescence, contributing to symptoms like inattention and poor emotional regulation.

3. Reduced Brain Volume

Overall brain volume, particularly in regions like the basal ganglia and cerebellum, is smaller in individuals with ADHD. The basal ganglia play a role in motor control and attention, while the cerebellum contributes to coordination and cognitive processes.

4. Dysregulated Dopamine Pathways

ADHD is associated with abnormalities in dopamine transmission. The dopamine system, essential for reward processing and motivation, may be less efficient, leading to challenges in maintaining sustained attention and motivation for tasks.

5. Abnormal Neural Responses to Emotion

Studies, such as those by Chronaki et al. (2015), show atypical neural responses to emotional stimuli. For example, children with ADHD exhibit a larger N100 brainwave for angry or happy voices compared to neutral voices, suggesting heightened sensitivity to emotional cues.

Depression: Neural Abnormalities

Depression is characterized by persistent sadness, loss of interest, and cognitive disturbances. Structural and functional changes in several brain regions underpin these symptoms:

SYMPTOMS OF DEPRESSIONS

1. Amygdala Overactivation

The amygdala, which processes emotions and stress responses, often shows hyperactivity in depression. This heightened activity is associated with an exaggerated response to negative stimuli, contributing to mood dysregulation.

2. Hippocampal Volume Reduction

The hippocampus, responsible for memory formation and emotional regulation, is frequently smaller in individuals with depression. This reduction is linked to difficulties in managing emotional memories and a heightened vulnerability to stress.

3. Prefrontal Cortex Hypoactivity

Similar to ADHD, the prefrontal cortex in depression is less active, especially in the dorsolateral prefrontal cortex. This contributes to impaired decision-making, concentration, and regulation of negative thoughts.

4. Impaired Connectivity

Functional connectivity between the amygdala and prefrontal cortex is often disrupted. This impairs the brain’s ability to regulate emotional responses, exacerbating symptoms of hopelessness and anxiety.

5. Neurotransmitter Imbalances

Depression is associated with deficiencies in neurotransmitters like serotonin, norepinephrine, and dopamine. These chemical imbalances affect mood, motivation, and energy levels, contributing to the disorder's hallmark symptoms.

DEPRESSION VS ADHD

Similarities and Contrasts Similarities:

• Both ADHD and depression involve abnormalities in the prefrontal cortex, impacting decision-making, impulse control, and emotion regulation.

• Dysregulated neurotransmitter systems, particularly dopamine, are central to both conditions.

Contrasts:

• While ADHD features heightened impulsivity and hyperactivity, depression is often marked by lethargy and withdrawal.

• The amygdala in ADHD is typically underactive or neutral, whereas it is hyperactive in depression.

Abnormalities in the brain

Hippocampus is responsible for memory and emotion and this is where depression is seen, they behave differently to those who haven’t got it.

Hippocampus tends to get smaller and smaller and grey matter shrinks and this part of the brain doesn’t function well.