Neural Plasticity

Lifespan Psychology: Neural Plasticity

LO

• To be able to outline adaptive and developmental plasticity.

• To describe the 5 stages of neural plasticity across the lifespan by completing review activities and a card sort.

Syllabus

• PKU 1.9 Role of neural plasticity in development through the lifespan- Adaptive and developmental plasticity

  • Stages of plasticity – proliferation, migration, synaptogenesis, synaptic pruning, myelination

  • Effect of changes in brain structures during adolescence – amygdala and pre-frontal cortex

Glossary

• Adaptive plasticity

• Developmental plasticity

• Proliferation

• Migration

• Synaptogenesis

• Synaptic pruning

• Myelination

• Amygdala

• Pre-frontal Cortex

Plasticity

• Infancy, adolescence = periods of rapid brain development.

• The brain is capable of learning throughout the lifespan because of its plasticity.

• Brain plasticity: The brain's ability to grow and reorganise neural connections in response to stimulation, necessary for learning, and present throughout life.

Adaptive and Developmental Plasticity

• Developmental (structural) plasticity: Neural connections form in response to sensory input; more changes occur in infancy, childhood, and adolescence.

• Adaptive (functional) plasticity: Neural connections reorganise to learn new information or compensate for lost functions; rerouting and sprouting can occur throughout life.

  • Examples: Stroke patients, Brain trauma patients

Key Definitions

• Rerouting: New connections are made between neurons to create alternate neural pathways.

• Sprouting: Existing neurons sprout new axons and dendrites that grow and make new connections with other neurons.

• Proliferation: The growth and division of cells, including neurons, that leads to the increase in total cell number.

• Migration: The movement of neurons throughout the brain.

• Synaptogenesis: Forming connections through electrochemical messages sent between neurons.

• Synaptic pruning: The reduction in the number of neurons, allowing remaining neural connections to strengthen and grow in complexity.

• Myelination: The growth of myelin over the axons of the neurons.

5 Stages of Plasticity (Developmental)

• Proliferation

• Migration

• Synaptogenesis

• Synaptic pruning

• Myelination

Infancy and Adolescence

• Infancy: Between birth and childhood (0 to 1 years of age).

• Adolescence: Between childhood and young adulthood (12/13 to 18/19 years of age).

Proliferation

• The growth and division of cells, including neurons, that leads to the increase in total cell number.

• Most neurons are formed in the fetal stage before birth.

• However, some neurons are still formed in infancy and early childhood.

Migration

• Newly formed neurons move outwards to their destined location.

• Positioning allows for connections between neurons (neural circuits) to be formed.

• The role of the neuron can be determined by where it is located at the time of its formation.

• Chemical trails left by other neurons guide or scaffolding fibres in the brain newly formed neurons to migrate to specific locations.

• Research suggests that migration finished at approximately five months old.

Synaptogenesis

• The axons of new neurons grow out to dendrites of target cells and form synapses with them, e.g., axons for motor neurons grow to the spinal cord where the neuron forms synapses with other neurons in this location.

• This allows the neurons to communicate with each other.

• During infancy and a small part of childhood, neural circuits form rapidly, especially in the primary sensory cortex and primary visual cortex.

Synaptic Pruning

• Infants are born with many more neurons than will ever be used - the excess will eventually be eliminated through pruning.

• A neuron that does not fire at the same time as its neighboring neurons is probably a neuron that has found its way into an inappropriate area during synapse formation and might be part targeted for pruning

• Elimination of excess neurons and synapses and those that have not established a connection with a neighboring cell will die.

• By removing this excess grey matter (neurons) the remaining connections can grow and increase in complexity

• Pruning occurs during infancy and childhood, and there is a second wave of pruning in early adolescence.

Synaptic Pruning Analogy

• Pruning is like a spring clean and throwing out all the junk you no longer use or need.

• Now when you want to get something specific, it is much easier to find.

Synaptic Pruning (Efficiency)

• Synaptic pruning increases the efficiency of the nervous system by allowing the remaining neural connections to strengthen and grow in complexity.

Myelination

• Where the axons of the neurons in a child’s brain become insulated by myelin, the last stage before the brain becomes fully mature.

• Myelin is a white, fatty, waxy substance that coats some axons and protects them from electrical interference from other neurons.

• Myelin speeds up the rate of transmission of signals within a neuron.

Myelination Timeline

• The myelination process begins before a baby is born and does not finish until about 23 years of age.

• Myelination starts in the spinal cord.

• Then, the lower structures of the brain (hindbrain, midbrain, and forebrain) are next to be myelinated.

• This is followed by the cerebral hemispheres, where myelination begins at the occipital lobes, followed by the temporal and parietal lobes and, finally, the frontal lobe.

Brain Plasticity and Learning

• Research has found that during this time of heightened brain plasticity, learning new skills, such as how to speak a second language or how to play a musical instrument, can be easier than in later life.

• Because a child's brain has greater plasticity than an adult's, they are able to use other parts of the brain to form alternative neural connections.

• A child's brain is also able to compensate for any missing or damaged part of the brain as a result of this plasticity.- E.g., it is more likely that a child will recover from damage to part of the brain responsible for language than an adult will.

Adolescence

• Stereotypical changes in behavior mark adolescence.

• Teenagers sleep more, experience mood swings, and have increased sensitivity to issues related to body image and sexual development.

• They also begin to engage in risky and novel-seeking behaviors such as reckless driving.

• Adolescence is characterized by immense changes – hormonally, physically, psychologically, and socially, which can explain some behaviors.

• However, modern neuroimaging studies have provided further insights and the relationship between these behaviors and an underdeveloped brain.

The Role of Brain Plasticity in Adolescence

• Circuit formation continues during childhood, and by approximately age 11 in females and 12 years old in males, the volume of grey matter is at its maximum.

• Synaptic pruning continues throughout adolescence and into early adulthood, increasing brain efficiency and specialisation of brain areas in response to sensory experiences.

• Loss of grey matter as a result of synaptic pruning progresses from the back to the front of the brain, with the prefrontal cortex being the last to structurally change

• The neural connections that remain after synaptic pruning undergo myelination, and while this process occurs in a few areas of the brain during adolescence, it does not occur in the prefrontal cortex until age 20.

• While young children can perform goal-directed behavior through planning, attention, and impulse control, these executive functions controlled by the prefrontal cortex are not able to be consistently used until the brain plasticity occurs during adolescence.

Key Brain Regions Undergoing Changes in Adolescence

• Prefrontal Cortex

• Amygdala

The Amygdala

• A part of the limbic system.

• A collection of nuclei deep within each temporal lobe that play a role in emotional response (including fear) and the immediate behavioral reactions to a response.

• It grows in volume during adolescence and becomes more active.

Amygdala Functions

• Roles of the amygdala include conditioning, a type of learning, the expression and regulation of emotions, particularly fear and aggression, social processing, and recognition of emotions.

• Human studies have shown that stimulation of the amygdala can intensify emotions and that psychopaths who struggle with recognizing fear have different activity in the amygdala than people who are not psychopaths.

• The combination of an overactive amygdala and an underdeveloped prefrontal cortex can explain the increase in risky behavior and mood swings in adolescents.

• They tend to experience heightened emotions but lack the cognitive function to help them regulate their responses, such as considering the consequences of their actions.

• This combination could also explain why adolescence is more susceptible to peer pressure.

• Neuroimaging studies have shown that, compared to adults, adolescents are more easily swayed by others (especially peers) and are worse at interpreting emotions in others due to their heightened reliance on their limbic system rather than the prefrontal cortex.

Amygdala and Prefrontal Cortex

• In adults, the prefrontal cortex regulates the amygdala, but during adolescence this is not the case, as the prefrontal cortex is still developing, as are other connections between the amygdala and prefrontal cortex.

• Instead of the prefrontal cortex leading actions based on rational and logical thinking, the volatile amygdala guides many of the automatic actions.

• The amygdala is highly reactive to emotional stimuli, such as facial expressions of other people and situations perceived as distressful.

• This leads to teenagers being more likely to misinterpret emotions of others in social cues and consequently get into accidents or behaving appropriately without thinking before they act.

Frontal Lobe

• The frontal lobe evaluates emotions and uses rational thinking and referring to past experiences before responding in a conscious manner.

• This control of voluntary behavior is not characteristic of teenagers as these lobes are one of the last regions of the brain to mature.

• The frontal lobes are not completely myelinated until around the age of 30; therefore, teenagers have less white matter (Myelinated axons) in this region compared to adults.

• Myelinated neurons improve connectivity between parts of the brain; with the frontal lobe not yet fully connected, the reduced ability to integrate information from brain regions affects cognition and emotional processors.

• The connection between frontal lobes and the amygdala is still strengthening during adolescence; therefore, teenagers may exhibit limited impulse control, poor decision-making and planning, and reduced emotional regulation.

Prefrontal Cortex

• The prefrontal cortex is the layer of the frontal lobes just beneath the forehead that continues to undergo myelination during adolescence, leading to an increase in white matter.

• In addition to myelination, synaptic pruning continues in the prefrontal cortex during this period of development, reducing the amount of grey matter and allowing for increasingly complex and efficient connections to be created in the brain.

• Synaptic pruning begins at the back of the brain and continues forward, with the prefrontal cortex being the last part of the brain to develop.

• This region is responsible for problem-solving, attention, and the ability to predict the consequences of behavior by referring to past experiences and assessing whether these behaviors will lead to reaching a desired goal.

• This makes it easier to understand why some teenagers do not seem to assess potential risks and end up engaging in risky and dangerous behavior.

• The ability to regulate emotion continues to improve during adolescence, as does the ability to recognise emotions in other people.