Developmental Brain Plasticity

• Focus on situationally induced brain plasticity, synaptic pruning, benefits, mechanisms, and implications when it goes awry.

• Event-driven brain plasticity discussed with navigation and the hippocampus and the effects of visual deprivation (e.g., learning Braille).

Synaptic Pruning

• Definition: The process where excess synaptic connections in the brain are eliminated during development to improve the efficiency of neural networks.

• Occurs particularly in the prefrontal cortex (PFC) around age 16 due to maturation and experience.

Mechanisms of Synaptic Pruning

• Neuronal connections that remain unused gradually deteriorate, which is correlated with increased cognitive performance.

• Key study: Sowell et al. (2001) analyzed 35 children aged 7 to 16 to investigate gray matter density in the frontal cortex and its relationship with cognitive function, finding that increased gray matter density correlates with improved memory functions, indicating brain maturation.

Effects of Experience on Synaptic Pruning

• Children aged 4 to 8 showed that higher rates of pruning (thinner cortical areas) predicted better working memory scores, though this does not imply causation. Study by Botdorf & Riggins with 186 children.

Mechanism of Pruning Process

• Involves microglia, which act as the brain's immune system, removing inactive synapses based on two major triggers: low activity levels of synapses and associated calcium ion levels.

• The process mirrors general brain functions repurposing them to prune unnecessary connections effectively.

Consequences When Pruning is Aberrant

• Consequences of Excess Pruning:

  • Correlated with conditions such as schizophrenia. Postmortem studies indicate a 16-23% decrease in dendritic connections in affected individuals.

  • Genetic studies connect this over-pruning to specific genes. Imaging studies reveal cortical thinning in regions typically rich in gray matter.

  • Elevated cerebrospinal fluid protein levels (C4) have been noted in first-episode schizophrenics, signaling excessive pruning activity.

• Consequences of Insufficient Pruning:

  • Linked to autism spectrum disorders (ASD), which exhibit less pruning in the temporal lobe. Studies compare autistic individuals with controls concerning synaptic spine density, finding greater retention of synapses in autistic brains.

Key Maturational Changes in the Brain

• Cognitive changes align with maturational changes in the brain:

  • White matter density increases through myelination continues until the third decade of life.

  • Prenatally, there is significant proliferation of axonic and dendritic branches, while postnatally, there’s an initial increase followed by synaptic pruning as a function of both experience and maturation.

  • Different areas of the brain (e.g., visual cortex, auditory cortex, prefrontal cortex) experience pruning at varied rates corresponding with cognitive advancements.

Clinical Correlates of Pruning

• References for further reading on clinical implications of synaptic pruning and its link to psychiatric disorders:

  • http://www.nytimes.com/2016/01/28/health/schizophrenia-cause-synaptic-pruning-brain-psychiatry.html

  • Reports on density of synaptic connections in autistic children indicating reduced pruning in comparison to control children.

  • Additional articles discussing brain synaptic density in autism and schizophrenia prevalent in late childhood.

Event-Driven Brain Plasticity

• Introduction of how psychological phenomena correlate with momentary cognitive and behavioral changes supported by independent neural changes. These changes occur incrementally as learning unfolds in response to experience.

Examples of Experience-Induced Behavior and Neural Changes

• Navigation skills (e.g., study of London taxi drivers illustrating brain structure and spatial navigation).

• Sensory deprivation cases such as studies on learning Braille; related to changes in the occipital lobe.

• Discussions on real-time studies using transcranial magnetic stimulation (TMS) to demonstrate brain adaptability over different modalities (e.g., new motor skills).

Conclusion on Brain Plasticity

• Brain plasticity encompasses multiple time scales,

  • Evolutionary changes driven by environmental adaptations and social behaviors.

  • Personal lifetime changes reflect correlated experiences, leading to shifts in gray and white matter densities.

  • Event-driven experiences direct the real-time organization of neural structures, impacting behavior and cognition at the synaptic and cellular levels through alterations in receptor counts and gray matter volumes effectively.