Neuroplasticity

What is neuroplasticity?

The capacity of the central nervous system to reorganise itself by forming, modifying and strengthening neural connections to both internal experiences and external stimuli

What is neural reorganisation and what is it dependent on?

Neural reorganisation can include both function - enabling and function disabling pasticity

The nature of the neural reorganisation depends largely on the inputs received and the outputs demanded post-lesion

List the mechanisms of neuroplasticity

Synaptic plasticity

Structural plasticity

Neurogenesis

Neuronal plasticity and network adaptations

what is synaptic plasticity?

• Change that occurs at synapses - the junctions between neurons - controls how effectively two neurons communicate with each other

• Fundamental mechanism involved in learning and memory

• Can result in either strengthening or weakening of synaptic connections - dependent on activity

structural plasticity

physical changes in neural architecture

1. Synaptogenesis: formation of new synapses

2. Dendritic branching: dendrites grow as cells adapt and respond to new information

3. Synaptic pruning: process of synapse removal

• Helps to refine neural networks and increase efficiency

• Occurs as part of brain maturation

• Structural plasticity is vital for re-establishing function after injury

Neurogenesis

• Refers to the generation of new neurons - in humans this occurs predominantly in the hippocampus and the subventricular zone

• Integral to learning, memory, emotional regulation and cognitive flexibility

• Declines with age

Neuronal plasticity; network adaptations and plasticity; functional reorganisation

• Changes in the electrophysiological properties of individual neurons - instantaneous (minutes to hours)

• Modifications in ion channel expression, metabolic activity, neurotransmitter density

• Can increase or decrease neuronal excitability and enhance responsiveness to incoming stimuli

• Large scale reorganisation of neural circuits and connectivity patterns - weeks to months

• Shifts in functional connectivity between brain regions

• Allows for adaptation to need experiences and learning

• Allows for compensatory mechanisms after injury

what is the same post-brain injury?

Processes of neural plasticity remain the same (i.e. behavioural demands drive neural plasticity)

what is different post-brain injury?

• The damaged neural environment complicates things

• Oedema, inflammation and altered neuronal excitability can significantly impair neuronal function

• When entire neural circuits are gone, structures that were not designed to perform a specific function may need to compensate

grey matter plasticity

• Synaptic plasticity occurs with motor learning, not with repetitive practice alone

• Relies on intensity, challenge, variability of practice, motivation, salience

 

white matter plasticity

• Remyelination of axons

• Axonal sprouting (expansion of new axonal branches from preexisting neurons) + Axonal remodelling

• Connectivity reorganisation (altered long range connection between regions)

• Activity = increased axonal firing = proliferation of oligodendrocytes

 

mechanisms of recovery after brain injury

1. spontaneous recovery

2. recruitment

3. retraining

4. structural connectivity changes

5. cortical reorganisation

6. window of heightened sensitivity

Spontaneous recovery

• Returning function to a brain area where the neurons were not lost but became dysfunctional following injury

• Spontaneous recovery/restoration - occurs in the early stages after injury

• Resolute of local oedema

• Improvement of local circulation

• Resorption of local toxins

• Recovery of partially damaged ischaemic neurons

Recruitment

 increasing the involvement of a brain area to perform a function that was lost after injury

Retraining

• adapting a brain area to perform a completely novel function

• Changes in structural connectivity and cortical reorganisation

Cortical reorganisation of motor skills

• Reorganisation of cortical maps are dependent on the cortical structure that was damaged

• Strokes that occurs in the motor cortex cause remapping of movement representation

• Can involve a change in spatial location in the brain

1. A greater degree of bilateral motor cortex activity

2. Increased recruitment of secondary cortical areas in the affected hemisphere

3. Increase in ipsilateral cortical involvement early on

window of heightened sensitivity

• Ischemia triggers

• Upregulation of genes responsible for neuronal growth (heightened neuroplasticity)

• Increases in long term potentiation, which enables strengthening of synapses and improved neurotransmission

• Alterations in excitation and inhibition via neurotransmitters

• Axonal sprouting around the infarct site

• Starts from a few hours after the stroke and lasts up to 3 months in humans

principles of experience

1. Use it or lose it

2. Use it and improve it

3. Specificity

4. Repetition matters

5. Intensity matters

6. difficulty: 11th principle

7. Time sensitive

8. Salience, motivation and attention

9. Age matters (a little)

10. Transference

11. Interference

Use it or lose it

• Failure to drive specific brain functions can lead to a functional degradation

Use it and improve it

• Training that drives a specific brain function can lead to an enhancement of that function

Specificity

• The nature of the training experience dictates the nature of plasticity

• Different motor training experiences, drive different patterns of neural plasticity

• Task specificity

  • Patients require task-specific training (skilled training) in order to drive neural plastic changes

  • Unskilled repetition of existing motor movements does not cause significant changes in the brain

  • Key message:  if you want your patient to learn to walk then you must practice walking

  • Specificity of timing:

    • We learn new motor skills by coordinating movements in time

    • Neurons that are synchronously activated tend to strengthen their connections between one another

Repetition matters

• Repetition is required to drive neural plasticity

• Total number of stimuli provided think 1000s of repetitio

Intensity matters

• Plasticity requires sufficient training intensity

• Total number of stimuli per until time

difficulty

• Induction of plasticity requires the appropriate level of difficulty

• Not too hard//not too easy

• Too easy = little behavioural demand = little change in behaviour

• Too hard = large behavioural demand = little change in behaviour

Time sensitive

• Neural restructuring should work anytime, however there is a time window in which it is the particularly effective, after brain damage

• Called lesion-induced reactive plasticity

Salience, motivation and attention

• The task to be learnt must be important to the individual

• Salience = increased attention = increased neural plasticity

Age matters (a little

• Reactive neuronal synaptogenesis declines

• Sprouting responses are less robust

• Synaptic replacement rates diminish

• However age should not be regarded as a limiting factor in the rehab of stroke patients

Transference

• Plasticity in response to one training experience can enhance the acquisition of similar behaviours

• i.e. the learning from one skill can be transferred to another

Interference

• Plasticity in response to one training experience can interfere with the acquisition of other behaviours

• i.e. the learning from one skill can interfere with the learning of another

5 key components of rehab program:

1. Task specific skill training

2. Neuromuscular training (e.g. muscle strength)

3. Flexibility

4. PT specific interventions to target impairments

5. Cardiovascular fitness/physical activity

+ advice, education and equipment prescription = OVERALL MANAGEMENT

Task specific or task orientated training of a skill

• Skill training = the acquisition and/or refinement of combinations of movement sequences

Task specific or task-orientated training

• Also known as functional task practice

• Practice of a relevant, real-world skill with the intention of acquiring it or reacquiring it

• It involves active participation of the patient, who focuses on achieving success at the task, in as realistic context as possible

• Quality of movement and safety

• Appropriate challenge

• Progress

Neuromuscular training

• Ask yourself - which muscles are weak and how are you going to strengthen them? Do you need to focus on strength, power or endurance?

• Need to be strengthened specifically for the task you are trying to retrain

• How does the muscle work in the particular functional task we are trying to acquire?

• Closed chain or open chain?

• Concentric or eccentric?

• Inner, mid and outer range?

• Speed of force production

Strength training

Power training

Endurance training

Flexibility 

• Ask yourself - which muscles/joints are at risk of adaptive changes?

• What positions/stretches are you going to incorporate?

• Passive ranging

• Positioning

• Stretching

• Flexibility habits

Cardiovascular and physical activity

• Patients with a neurological injury are less active compared with their peers

• Interventions that focus on maintenance of improving aerobic fitness have the benefits of:

• Increasing balance, walking ability and walking speed

• Positive affects on cardiovascular function

• Neuroprotective affects/supports neuroplasticity

• Improves memory, attention and executive function

• Reduces depression and anxiety

• Increases quality of life

Specific physiotherapy modalities

• Management of impairments that are interfering with function

• Require specific physiotherapy assessment and management separate to other categories - respiratory function, pain, oedema, subluxation, joint stiffness, vestibular dysfunction, visual deficits, sensory deficits, neglect, spasticity, fatigue

When should rehab start?

• For acute patients: as soon as they are medically stable

• For chronic patients/neurodegenerative conditions: as soon as they are referred

• All stroke patients should commence out of bed activity within 48 hrs of stroke onset unless receiving palliative care

How much physiotherapy should they have?

• Learning is directly related to the type and amount of practice

• Repetition +++

• Fatigue and quality of movement should guide the therapist as to intensity and repetitions

• Stroke foundation recommendation:

• A minimum of 3 hours a day of therapy (occupation therapy and physiotherapy) should be provided for stroke survivors, at least 2 hours of active task practice)

How can we increase practice time?

• Circuit classes and use of workstations

• Independent practice both inside and outside therapy time, alone or with family

• Requires structure, safety and feedback

• Forced use paradigms (i.e. constraint induced movement therapy)

• Goal setting

• Fostering self-management

• Mental practice

Circuit classes/group therapy approach

• Group therapy involving task-specific training should be used to increase the amount of practice in rehabilitation

• The use of circuit classes is a strong recommendation for the treatment of stroke

Independent practice

• Have an "open door policy" in the gym

• Active practice

• Positioning/ranging exercises

• Specific exercises with specific goals

• Functional activities that can be safely performed

• Use practice books with clear description of exercise, dosage and goals

• Ensure safety

• Mental/verbal rehearsal of tasks

• Mental imagery has been shown to be useful in neurorehabilitation

Designing a rehab program

Remember the following:

• Brain is plastic and able to change

• Brain learns what is practiced - task specificity

• Skill acquisition requires - repetitive practice, intense practice, challenging practice

• Learning requires - active participation

• The PT needs to be an effective coach and motivator