Structural Changes of the Brain

The brain is a complex system of highly interrelated elements, and its successful development requires that each component be formed in a timely, fully integrated manner with the others.  This process happens throughout four stages, each being crucial for the functional and structural components of our brains. The processes are:

• Neurogenesis 

• Migration

• Differentiation

• Pruning

Brain Development

• A complex system of interrelated elements

• Successful development requires timely, complete, and correct integration of components.

Neurogenesis 

• Involves the production of new nerve cells (neurons), which help transmit information throughout the nervous system.

  • Neurons play major roles in various cognitive functions, including but not limited to mood regulation, cognitive flexibility, and memory encoding.

  • Neurons contribute to various cognitive and functional aspects of human life, such as mood regulation, memory encoding, flexibility, and more.

• Neurogenesis is a critical stage of structural change 

  • It sets the foundation for brain function

  • While neurogenesis mostly occurs during early development, it can still happen during adulthood.

Migration 

• The neurons produced in neurogenesis migrate to their “designated” location around 9 weeks after conception

• They travel along glial fibers which are supported by the central nervous system

• These fibers go from the brain’s inward structure to the cortical layers

  • Glial Fibers: non-neuronal cells in the central nervous system that form early in the fetal brain

    • Function: provide support and protection for neurons

Process

As the brain grows, the glial fibers stretch and curve, these fibers then form pathways that direct neurons to the “correct” position in the brain

• Neurons “climb” along the fibers like a snake of a tree

• At the cells' final position, dendritic growth starts

  • Dendritic growth: allows neurons to connect with other neurons

• The process then begins building layer-by-layer, progressing outward from the brain cortex (outermost layer of the brain, located on the top of your cerebrum

Neuronal Growth

• Neuronal growth occurs in the brain cortex

  • New neurons form below the previously layers 

  • The new neurons then travel outside while passing existing layers of neurons 

Differentiation 

• The growth of connections between neurons (synapses)

  • Synapse: a junction between two nerve cells, consisting of a minute ages across which impulses pass by diffusion of a neurotransmitter

• Synapses start growing shortly after conception 

• Eventually becomes rapid, with 40,000 synapses per second

• Rapidness continues until nearly 2 years of age 

• This is followed by a plateau and then a rapid reduction of the number of synapses

Pruning 

• The elimination of the connections between neurons made in Differentiation 

• Elimination of neurons themselves 

• Elimination occurs at a rate of 100,000 synapses per second

Timing 

• Pruning is most active during childhood and adolescence, correlating with critical periods of learning and development.

• The brain undergoes significant reorganization during these periods, allowing for the acquisition of complex skills and adaptive behaviors.

• Pruning lasts until the end of puberty

  • At this point, around 50% of initially formed synapses are eliminated 

• This is followed by another plateau and then another drop in the number of synapses in old age 

Lifespan Changes

• Synaptic pruning continues into old age

• Contributes to changes in cognitive functions associated with aging

• The balance between synapse formation and pruning shifts throughout life

• Reflects the brain's ongoing adaptation to experiences and environmental demands

Impact on Cognitive Development 

• Efficient pruning is essential for healthy cognitive development.

• Excessive or insufficient pruning can lead to neurological and psychiatric conditions.

• Excessive pruning has been linked to disorders such as schizophrenia.

• Insufficient pruning is associated with autism spectrum disorders.

Brain Structure-Function Relationship

Complexity and Maturation

Understanding human psychological development involves more than just changes in brain structure. 

It requires integrating knowledge across several domains:

• Structural Changes: While structural changes in the brain occur throughout development, they alone cannot fully explain psychological maturation.

• Integration of Knowledge: To gain a comprehensive understanding, it's essential to combine insights from studies on structure-function relationships in the adult brain, behavioral changes observed in adults with brain lesions, and evidence from advanced neuroimaging techniques.

Synaptic Density and Cognitive Abilities

• Infants vs. Adults

  • Infants have a higher synaptic density compared to adults. 

  • This abundance of synaptic connections reflects the brain's plasticity early in life.

• Misconceptions

  • Having more synaptic connections does not necessarily translate to superior cognitive abilities. 

  • Synaptic pruning plays a critical role in cognitive development.

    • It refines and strengthens essential connections

• Supporting Studies

  • Werker and Tees (1992)

    • Focus: Studied infants' ability to discriminate phonemes from English and Hindi.

    • Method: Used the High-Amplitude Sucking (HAS) technique to measure infants' responses to speech sounds

    • Findings:

      • Infants initially discriminated between speech sounds from both English and Hindi.

      • Infants primarily discriminate speech sounds from their parents' language by one-year-old.

      • Showed synaptic pruning refines cognitive abilities, focusing sensitivity on native language sounds.

    • Significance: Emphasized synaptic pruning's role in language development, illustrating how early experiences shape perceptual abilities.

Historical and Modern Methods of Study

Understanding brain development has evolved from early post-mortem studies to modern neuroimaging techniques. Initial studies focused on brain size, which increased until about 9-10 years old, but didn't directly determine cognitive ability. The advent of MRI and PET scans enabled real-time insights, emphasizing neuronal connectivity over brain size.

Early Studies

• Post-Mortem Studies: Early understanding of brain development was primarily derived from post-mortem studies focusing on brain size and anatomical features.

• Limitations: While these studies provided foundational insights, they were limited by their inability to observe dynamic changes in the living brain and their focus on anatomical rather than functional aspects.

• Findings: They revealed that brain size increases steadily until around 9-10 years of age. However, the relationship between brain size and cognitive ability is not linear, underscoring the need for more nuanced approaches to studying brain development.

Brain Imaging Technologies

• Advancements: The advent of modern brain imaging technologies, such as MRI (Magnetic Resonance Imaging) and PET (Positron Emission Tomography), has revolutionized our ability to study the brain in real time.

• Significance: These technologies enable researchers to examine not only the structural aspects of the brain but also its functional organization and activity patterns. This shift has emphasized the importance of neuronal connectivity and networks over simple measures of brain size or density.