6. Neuroplasticity

neuroplasticity

brain’s capacity to physically change in response to development, experience, damage, or dysfunction

plasticity mechanisms

axonal sprouting (structural level)

dendritic branching (structural level)

pruning (structural level)

synaptic plasticity

• homosynaptic plasticity

• heterosynaptic plasticity

functional modular plasticity (network level)

• homologous area adaptation

• cross-modal reassignment

• map expansion

• compensatory masquerade

axonal sprouting

new growth from one growth cone - developing axons

• growth cone is navigator of axon: fan shaped tip; probes environment by extending and retracting membranous projections called filopodia and lemelliopodia

• axon outgrowth and guidance to targets depends on coords; ination of cytoskeletal proteins (actin and microtubules) and environmental guidance cues

  • protrusion: extension of new membrane at the edges of the growth cone

  • engorgement: microtubule driven transport of organelles and vesicles into the peripheral regions

  • consolidation: stabilization of the proximal growth cone into a cylindrical axon shaft

• collateral sprouting from healthy axons: allow axons to make multiple connections with various targets

  • occurs during development and in response to injury/disease

protrusion: axonal sprouting

• protrusion: extension of new membrane at the edges of the growth cone

engorgment: axonal sprouting

• engorgement: microtubule driven transport of organelles and vesicles into the peripheral regions

consolidation: axonal sprouting

• consolidation: stabilization of the proximal growth cone into a cylindrical axon shaft

bottom is cut axon

dendritic branching and spine formation

involves cytoskeletal proteins (predominately actin)

occurs during development in response to experience

dynamic: branching nd spine re-modeling correlates with enriched environments, learning, memory

dendritic spine morphology varies between apical and basal dendrites

apical dendrites may be more sensitive to age related changes

abnormalities in dendritic branching and spine formation implicated in brain disorders (ASD, Schizophrenia)

synaptic pruning

process of removing synapses as part of brain maturation

plasticity

dynamic process of axonal and dendritic branching/elimination, spine formation/elimination underlie synaptic remodeling resulting in changes of wiring of the brain

changes occur in response to development, injuries, dysfunction, experience

synaptic plasticity: homosynaptic plasticity

only neurons that are specifically innervated undergo changes in synaptic plasticity

synapses that were directly activated at the time of the information transfer

heterosynaptic plasticity

synaptic pathways not specifically stimulated undergo changes

long-term potentiation

synaptic strengthening

high frequency stimulation, glutamate released from presynaptic cell to postsynaptic

depolarization

influx of calcium into postsynaptic membrane receptors

more amberoceptors into membrane

responds more strongly to future releases of glutamate

long term depression

synaptic weakening

low frequency stimulation

glutamate release; depolarization

small influx of calcium

subsequent releases results in weaker response

functional modular plasticity: homologous area adaptation

damage to brain region can be compensated for; shifting operation to other areas

allows for the shifting of operations from one region of the brain to another region

specific process is carries out by homologous region in opposite hemispherefu

functional modular plasticity: cross-modal reassignment

an area that previously processed a specific type of sensory input now receives input from another sensory source

functional modular plasticity: map expansion

representational area carrying out a specific function expands as a result of the performance of that function or repeated exposure to a stimulus

functional modular plasticity: compensatory masquerade

reorganization of preexisting neural networks allowing performance of a function to be carried out successfully in the absence of networks that previously supported that functionp

promoting neuroplasticity

maximize activity-dependent plasticity

• train impaired limb (skilled limb movements)

• start early

• avoid compensation

• high-dose training

  • challenge participant

task-oriented training

task gradation and progression

• tasks graded to match motor capabilities: challenge; do not overwhelm

• grade up or grade down

10 principles of experience dependent neuroplasticity

• How can activity-dependent plasticity be amplified? OT!! 

• Upper extremity recovery post-stroke as a model: 

▪ Which limb? – think - paretic limb

What kind of training? – think - goal directed activities (functional, motivating, stimulating, challenging, etc.) aimed at reducing impairments– avoid compensation! *Remember the challenge for us will be striking an appropriate balance!! 

▪ When to start? – think – ASAP!! 

How much? – think – high dosage – lots and lots of repetitions – but remember needs to be challenging/motivating/stimulating, etc…. So repetition without repetition – lots of repeated movements but with some variability/novelty (e.g. reach to grasp items of various sizes placed in various locations in the workspace - not one item in one location over and  over again!)