Brain Plasticity and 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.

  • Genetic information (nature) and experiences (nurture) shape the brain's structure and organization.

  • Neurons are the building blocks of the nervous system, organized into neural pathways.

  • Information continuously travels through these pathways.

  • Neurons and their connections change in response to experiences, enabling learning and memory.

  • Forming new connections in the brain allows you to remember what you learn.

  • Repetition strengthens connections, reinforcing memory.

  • The brain can 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 link up or interconnect with existing ones.

  • Changes occur to the brain's physical structure and function.

  • The brain reorganizes based on overuse, underuse, or injury.

  • Examples:

    • Brain development in youth.

    • Learning throughout life.

    • Drug use.

    • Brain injury.

  • The brain's overall shape doesn't change; changes happen at a cellular level.

Factors Influencing Brain Plasticity

  • Genes provide the biological basis for plasticity, but experiences influence the process.

  • The type and timing of experiences are influential.

  • Two types of plasticity in the healthy brain:

    • Experience-expectant plasticity

    • Experience-dependent plasticity

Experience-Expectant Plasticity

  • Brain change in response to expected environmental experience.

  • Occurs largely during development; species-wide (occurs in all members of a species).

  • Example: Exposure to light and patterned visual information for visual cortex development.

  • Specific brain structures require specific environmental input at certain times.

  • If the experience doesn't occur when expected, brain development may be impaired.

Experience-Dependent Plasticity

  • Brain change that modifies existing neuronal structures.

  • Occurs when learning something new.

  • Based on experiences unique to each individual; can occur at any time.

  • Not time-dependent; no sensitive or critical period.

  • Brain structure changes in relation to the experience; influenced by intensity/frequency. For e.g. Pianists have larger cortical areas for finger control.

Neuroplasticity in Response to Brain Injury

  • Experience-dependent plasticity occurs in response to brain injury.

  • Enables the brain to recover or compensate for lost function.

  • Also called functional or adaptive plasticity.

  • How the brain changes depends on the cause, location, degree, extent, and age at injury.

  • Some brain areas (hindbrain, brainstem) don't recover easily.

  • Severe injuries may result in indefinite life support/coma.

  • Recovery is more likely in infants and children due to greater plasticity.

Types of Change

  • Neuroplasticity enables compensation/recovery by reorganizing the structure.

    • Generating new neural connections/pathways.

    • Changing intact neuronal networks.

  • Sprouting: Damaged neurons grow new connections to replace lost ones.

  • Generation of new networks allows functions to shift from damaged to undamaged areas; brain function lost through injury is rerouted via new connections.

  • Neurons need stimulation through repetitive activity to reconnect/form new connections.

  • Individuals may need to relearn tasks.

  • Successful relearning is more likely in younger individuals.

Rerouting and Sprouting

  • Rerouting: New connections 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 areas of the brain can sometimes be reassigned to other undamaged areas of the brain to compensate for changing input from the environment as a result of Neuroplasticity.

  • Neurogenesis: the production or ‘birth’ of new neurons. Evidence suggests a role for adult-generated neurons in learning and memory, and for treatment of neurodegenerative disorders and brain injuries.

Types of Brain Injury

  • Brain injury: any type of brain damage or disorder that impairs or interferes with the normal functioning of the brain, either temporarily or permanently.

  • Acquired brain injury: any type of brain damage or injury that occurs after birth.

  • Brain injury is common.

    • Estimated that about 1 in 45 Australians have a brain injury that impairs everyday life in some way.

    • Three out every four of them 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, and degenerative brain disorders.

  • 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 organize, 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 Acquired Brain Injury

  • Sudden onset (blow to the head, infection, stroke, drug overdose) or gradual development (prolonged substance use, tumor, degenerative disease).

  • Impairments can affect physical/cognitive/emotional/behavioral functions.

  • Impact depends on individual, nature, location, severity, and timing of treatment.

Psychological Impacts

  • Memory problems.

  • Difficulty problem-solving.

  • Poor concentration and attention.

  • Reduced ability to organize 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 (irritability, anger).

  • Slowed responses.

  • Impulsive behavior and/or a lack of emotional control.

Biological Impacts

  • 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.

Social Impacts

  • Social isolation (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

  • Definition: A type of acquired brain injury caused when an external force causes damage to the brain.

  • Examples:

    • Blow to the head.

    • Head forced to move rapidly forward or backward.

    • Object pierces the skull and enters brain tissue.

  • Causes: fall, motor vehicle accident, sporting accident, a ‘king hit’, repeated blows over time in contact sports.

  • Brain slams against the inside of the skull.

  • Brain tissue may bleed, bruise, stretch, tear, twist, or become swollen.

  • Neurons may be killed or starved of oxygen and nutrients.

  • Effects can be mild, moderate, or severe.

  • Momentary or long-term loss of consciousness.

Aphasia

  • Definition: A language disorder resulting from acquired brain injury to an area responsible for language production or processing.

  • Difficulties in expressing oneself, understanding speech, reading, and writing.

  • The type and severity depends on the location and extent of damage.

  • Aphasia does not affect intelligence, and it is not a mental health disorder.

  • The disorder may change over time through speech and language therapy contributing to neuroplasticity.

  • Improvement tends to be a slow process, generally viewed as not curable.

  • If caused by a stroke and the symptoms of aphasia last longer than 2 or 3 months after a stroke, a complete recovery is unlikely.

Types of Aphasia

  • Fluent aphasias: speech is easily produced and flows freely (i.e. fluent) but the 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: there are specific impairments in reading (alexia), writing (agraphia) or recognising spoken words despite being able to hear them (word deafness).

Broca's Aphasia (Non-Fluent)

  • Damage to Broca's area (left frontal lobe).

  • Difficulty producing speech.

  • Speech is labored, hesitant, short sentences (3-4 words), mainly verbs and nouns; small parts of speech omitted.

  • Reading and writing may also be impaired.

  • Speech comprehension is good for everyday conversation, but difficulty understanding complex speech/instructions.

  • Aware of their language difficulties.

Wernicke's Aphasia (Fluent)

  • Damage to Wernicke's area (left temporal lobe).

  • Difficulty understanding spoken or written language and speaking in a meaningful way.

The human brain exhibits neuroplasticity, which is its ability to change throughout life based on experience. This includes forming new neural connections and reorganizing existing pathways in response to learning or injury. Factors influencing this plasticity include genetics, specific experiences, and timing. There are two types of plasticity: experience-expectant, which occurs during development, and experience-dependent, which happens when learning something new.

In cases of acquired brain injury, neuroplasticity enables recovery by allowing the brain to compensate for lost functions, although recovery varies based on the type and severity of the injury. Types of brain injuries range from mild to very severe, affecting physical and cognitive abilities. Psychological impacts may include memory problems and mood changes, while biological impacts could manifest as movement disorders. Social consequences involve challenges in relationships and work capabilities. There is also trauma-related brain injury that results from external forces, leading to varying degrees of damage and symptoms. Aphasia, a language disorder resulting from brain injury, can affect speaking and understanding but does not affect intelligence. Types of aphasia include fluent, non-fluent, and pure