Brain Plasticity and Brain Injury Notes

Brain Plasticity and Brain Injury

Overview

  • Factors influencing brain plasticity
  • Impact of an acquired brain injury
  • Chronic traumatic encephalopathy (CTE)

Introduction

  • No two human brains are identical.
  • Brain development is influenced by:
    • Genetic information (nature)
    • Experiences (nurture)
  • Neurons are the building blocks of the nervous system.
  • The entire nervous system is comprised of neurons organised into neural pathways.
  • Neurons and their connections change throughout life in response to experiences, enabling learning and memory.
  • Repetition strengthens neural connections and memories.
  • The brain can sometimes repair itself, with healthy areas taking over functions of damaged areas.

Neuroplasticity

  • Definition: The ability of the brain and nervous system to change in response to experience.
  • Neurons and their connections are modified.
  • New neural pathways form and existing pathways interconnect.
  • Changes occur in the brain’s physical structure and function.
  • The brain reorganises its neural connections based on overuse, underuse, or injury.
  • Examples of when neuroplasticity happens:
    • Brain development in youth
    • Learning throughout life
    • Drug use
    • Response to brain injury
  • Change occurs at the microscopic, cellular level.
  • Some brain areas (e.g., sensory and motor cortices) have higher plasticity.
  • Younger brains are more plastic, especially during sensitive periods.
  • Children learn languages faster and recover from brain injuries more quickly due to greater plasticity.

Factors Influencing Brain Plasticity

  • Genes provide the biological basis, but experiences influence the process.
  • The type and timing of experience are influential.
    • Experience-expectant plasticity
    • Experience-dependent plasticity

Experience-Expectant Plasticity

  • Brain change in response to expected environmental experiences.
  • Occurs largely during development.
  • 'Species-wide': all members of a species usually have the experience.
  • Example: Exposure to light and patterned visual information for normal visual cortex development.
  • Specific brain structures need specific experiences at certain times to develop according to genetic instructions.
  • If the expected experience does not occur during its sensitive period, brain development may be impaired.

Experience-Dependent Plasticity

  • Brain change that modifies existing neuronal structures.
  • Occurs when learning something new.
  • Unique to each individual and can occur throughout the lifespan.
  • Not time-dependent, no sensitive or critical period.
  • The brain’s structure changes in relation to the intensity and frequency of the experience.
  • Example: Concert pianists have larger cortical areas for finger control.

Neuroplasticity in Response to Brain Injury

  • Enables the brain to recover from or compensate for lost function and maximise remaining functions.
  • Also referred to as ‘functional plasticity’ or ‘adaptive plasticity’.
  • How the brain changes depends on:
    • Cause, location, degree, and extent of damage
    • Age at injury (neuroplasticity is age-dependent)
  • Some brain areas (especially hindbrain or brain stem structures) do not recover easily.
  • Severe injuries to these areas can lead to a coma.
  • Recovery from traumatic brain injury is usually more likely in infants and children, but not always.

Types of Change

  • Neuroplasticity enables the brain to compensate or recover by reorganising its structure.
    • Generating new neural connections and pathways
    • Changing remaining intact neuronal networks

Sprouting

  • Damaged neurons grow new connections to replace lost ones.

Generation of New Networks

  • Functions shift from damaged to undamaged areas.
  • Neurons that have lost a connection seek new neurons to connect with.
  • Brain function lost through injury is rerouted via new connections.
  • Neurons need stimulation through repetitive activity to reconnect or form new connections.
  • A person with a brain injury may need to relearn tasks.
  • Younger individuals have a greater likelihood of successful relearning and new learning.

Rerouting and Sprouting

  • Rerouting: New connections are made between active neurons to create alternate neural pathways
  • Sprouting: New axon and dendrite extensions allow existing neurons to form new connections

Types of Change

Reassignment of Function

  • Functions performed by certain brain areas can be reassigned to undamaged areas to compensate for changing input.
  • For example, when a function is taken over by the opposite cerebral hemisphere.

Neurogenesis

  • The production or ‘birth’ of new neurons.
  • Offers possibilities for treating neurodegenerative disorders and brain injuries and for learning and memory.

Acquired Brain Injury

  • Definition: Any type of brain damage or disorder that impairs normal brain functioning, either temporarily or permanently, that occurs after birth.
  • Common: Estimated that about 1 in 45 Australians have a brain injury.
  • Three out of four are aged under 65.
  • As many as two out of every three of these people acquired their brain injury before they turned 25.
  • Three out of every four people with acquired brain injury are male.

Causes of Acquired Brain Injury

  • Falls, sporting incidents, intentional blows to the head, violent shaking of the head
  • Alcohol and other drugs, lack of oxygen, brain surgery, infection (such as meningitis)
  • Stroke, brain inflammation (such as encephalitis), epilepsy
  • Degenerative brain disorders such as Parkinson’s disease, Alzheimer’s disease, motor neurone disease, and chronic traumatic encephalopathy (CTE)
  • Injuries sustained by infants in the uterus such as Foetal Alcohol Spectrum Disorder

Severity of Brain Injury

  • Mild: Good recovery, limited concentration, able to return to work.
  • Moderate: Improvement over time, difficulties with coordinating movements, inability to organise, may require different line of work.
  • Severe: Decreased movement control, decreased ability to communicate, requires support with daily living, unable to return to work.
  • Very severe: Unable to control movement, unable to communicate, requires 24-hour support, unable to return to work.

Impact of an Acquired Brain Injury

  • Sudden onset (e.g., blow to the head, infection, stroke, drug overdose) or gradual development (e.g., prolonged substance use, tumor, degenerative brain disease).
  • Impairments can affect physical, cognitive, emotional, and behavioral functioning.
  • Impact depends on the individual, the nature, location, and severity of the injury.
  • Timing of appropriate treatment is vital for recovery.

Impact of an Acquired Brain Injury

  • Biological:
    • Movement disorders
    • Dizziness and balance problems
    • Eyesight, hearing problems
    • Loss of taste and smell
    • Headaches
    • Chronic pain
    • Impaired speech, reading, writing
    • Fatigue and sleep problems
    • Hormonal imbalances
  • Psychological:
    • Memory problems
    • Difficulty problem-solving
    • Poor concentration and attention
    • Reduced ability to organise and plan
    • Lack of initiative and motivation
    • Lack of insight and awareness, and poor judgment
    • Loss of self-esteem
    • Personality changes
    • Distress, anxiety, panic attacks
    • Mood disturbance, (e.g., irritability, anger)
    • Slowed responses
    • Impulsive behavior and/or a lack of emotional control
  • Social:
    • Social isolation, (e.g. difficulties in making and keeping friends)
    • Altered personal relationships
    • Disrupted family relationships
    • Changes to living arrangements
    • Social role changes
    • Different vocational capabilities
    • Different educational opportunities
    • Financial hardship
    • Legal restrictions
    • Social stigma

Traumatic Brain Injury

  • A type of acquired brain injury caused by an external force damaging the brain.
  • Can result from a blow to the head, rapid head movements, or an object piercing the skull.
  • Causes include falls, motor vehicle accidents, sporting accidents, or repeated blows.
  • Brain tissue may bleed, bruise, stretch, tear, twist, or become swollen.
  • Neurons may be killed outright or starved of oxygen and nutrients.
  • Effects can be mild, moderate, or severe.
  • May be a momentary loss of consciousness or a long-term coma.

Aphasia

  • A language disorder resulting from an acquired brain injury to an area responsible for language production or processing.
  • Individuals may have difficulty expressing themselves, understanding speech, and with reading and writing.
  • The type and severity of language impairment depend on the location and extent of brain tissue damage.
  • Aphasia does not affect intelligence and is not a mental health disorder.
  • May change over time through speech and language therapy, contributing to neuroplasticity.
  • Improvement tends to be slow and is generally viewed as not curable.
  • If caused by a stroke and symptoms last longer than 2 or 3 months, complete recovery is unlikely.

Types of Aphasia

  • Fluent aphasias: Speech is easily produced and flows freely, but sentences don’t make sense, and the person often has difficulties understanding what is heard or read (e.g., Wernicke’s aphasia).
  • Non-fluent aphasias: Difficulties in speaking clearly, often in short sentences with words omitted; speech is effortful and includes only key words necessary for communication but no difficulties understanding what is heard or read (e.g., Broca’s aphasia).
  • Pure aphasias: Specific impairments in reading (alexia), writing (agraphia), or recognising spoken words despite being able to hear them (word deafness).

Broca’s Aphasia (Non-Fluent Aphasia)

  • Damage to Broca’s area (left frontal lobe).
  • Most commonly due to stroke.
  • Difficulty producing speech; speech is labored, hesitant, and consists of short sentences with mainly verbs and nouns.
  • Small parts of speech are omitted, as are proper grammatical endings.
  • Example: ‘went house, visit cousin’.
  • Reading and writing may also be impaired.
  • Speech comprehension is good for everyday conversation, but difficulty understanding complex speech and lengthy instructions.
  • Individuals are usually aware of their language difficulties and have a clear understanding of their condition.

Wernicke’s Aphasia (Fluent Aphasia)

  • Damage to Wernicke’s area (left temporal lobe).
  • Most commonly due to stroke.
  • Difficulty understanding spoken or written language and speaking meaningfully.
  • The individual hears the voice or sees the print but cannot make sense of the words.
  • Speech is fluent but nonsensical; often sounds like a word salad.
  • Example: ‘I feel very well. In other words, I used to be able to work cigarettes. I don’t know how. Things I couldn’t hear from are here’.
  • Individuals have little or no conscious awareness or understanding of their condition and lack awareness that others cannot understand them.

Concussion

  • A type of traumatic brain injury caused by a blow to the head or a hit to the body that causes the head and brain to move rapidly back and forth.
  • This movement can cause the brain to bounce around or twist in the skull, disrupting neuronal activity and sometimes damaging brain tissue and cells.
  • Concussions can occur during:
    • A sporting injury, particularly in body contact sports, such as boxing, AFL football and rugby
    • Horse riding, cycling, skiing and trail bike riding
    • Whiplash injury in a car accident
  • A ‘black out’ or loss of consciousness is not required for the diagnosis of concussion.
  • Concussions are commonly described as ‘mild’ brain injuries because they are usually not life-threatening, symptoms are short-lived and people return to normal functioning fairly quickly.
  • However, the effects of a concussion can be serious when a person has a previous history of concussion.

Chronic Traumatic Encephalopathy (CTE)

  • Progressive brain degeneration and fatal condition thought to be caused by repeated blows to the head and repeated episodes of concussion.
  • Particularly associated with contact sports.
  • Rare disorder that is not yet well understood.
  • First diagnosed in the early 2000s during an autopsy of the brain of a former professional (American) footballer.
  • Over the last few years, CTE has been identified in ex-players of Australian Rules football, rugby league, and rugby union.
  • There’s still some debate about how common CTE is, its symptoms and its diagnostic criteria.

CTE Symptoms

  • Symptoms vary between individuals.
  • Generally, symptoms are initially mild but progress over time to become more severe.
  • Symptoms may not be experienced until years or decades after the brain injury occurs.
  • Symptoms may include:
    • Loss of memory, (e.g. asking the same question several times, or having difficulty remembering names)
    • Mood changes, (e.g. frequent mood swings, depression, feeling increasingly anxious, frustrated, agitated)
    • Personality changes
    • Difficulty controlling impulsive or erratic behavior
    • Increasing confusion and disorientation, (e.g. getting lost, wandering or not knowing what time of day it is)
    • Difficulty thinking, (e.g. finding it hard to make decisions, impaired judgments)
    • Motor impairments, (e.g. involuntary movement (tremor), slow movements, difficulty with balance, slurred speech).

CTE Diagnoses and Treatment

  • There is currently no medical or psychological test to diagnose CTE in a living person.
  • Changes to the brain don’t always show up on brain scans, and if they do, they may be similar to other conditions.
  • Diagnosis is primarily based on a history of participating in contact sports and the symptoms the individual presents.
  • If CTE is suspected, a range of assessments may be undertaken to rule out other causes.
  • CTE can only be properly diagnosed in an autopsy by examining sections of the brain for atrophy and the presence of an abnormal build-up of tau.
  • As with most other types of neurodegenerative brain disorders, treatment for CTE is based around supportive treatments.

CTE Research

  • Not all athletes who experience repeated concussions or people with a history of head or brain injuries go on to develop CTE.
  • In addition, CTE has been diagnosed in people without a history of head or brain injuries.
  • According to Sports Australia (2022), the link between sport-related concussion and CTE is based on ‘low-level evidence’.
  • The contribution of potential confounding variables, such as genetic predisposition, alcohol and drug use or a co -existing dementia, ‘is not adequately accounted for in the research evidence’.
  • More research is needed to learn about the causes of CTE, its symptoms, and how it affects the brain.
  • In particular, research on the role of genetics, age at first concussion, physical health, and other factors (such as environmental or lifestyle factors) is needed to better understand the risk factors for CTE.