Topic 20 Plasticity and recovery of CNS following insult

Question 1

Discuss the physiology of functional recovery following an insult to the CNS

Answer 1

• Immediately following stroke the CNS is in shock (no electrical output, no movement)
• Direct neuronal damage
• Increased inhibitory activity to protect CNSfrom further damage

This is followed by spontaneous neurologic recovery which is:
• a prompt initial improvement in function as the pathologic processes associated with the penumbra-ischemic metabolic injury, edema hemorrhage, and blood pressure (BP) resolve.
• The time frame for recovery of function in these reversibly injured neurons is relatively
short, accounting for improvement in the first several weeks.

• There is: an initial restitution of CNS activity (days to weeks depending on size of lesion) (some electrical output, some movement)
• Regression of oedema
• Degradation of necrotic tissue

2 mechanisms of recovers
-Spontaneous recovery 3-6 months

Question 2

2 mechanisms of recovery from stroke

Answer 2

• Spontaneous Recovery-(3-6 month period)
Recovery of neural tissue, movement and activity as it was prior to insult (lost functions are restored)
• Diaschisis reversal- return to same circuits
• Cortical reorganization- neurogenesis, axonal
sprouting, dentritic growth, synaptogenesis,
angiogenesis
• Changes to movement patterns

• Training Induced Recovery-(not necessarily time limited)
Compensation recruitment of new neural circuits, training of new
movement and activity (new movements/functions acquired)
• Compensation- new brain areas or neural networks enlisted to complete previous functions
• Synaptogenesis- increase in size and complexity of arbor, increased number of dendritic spines and synapse excitability
• Synaptic plasticity- LTP (increased efficiency)

Question 3

Describe the 10 elements of experience dependent plasticity

Answer 3

Experience dependent plasticity
1. Use it or lose it
Degradation of neural circuits over time if not actively engaged .Evidence that rehabilitation can protect neurons and networks that would otherwise be lost after brain injury. * timing very important
2. Use it and improve it Cortical reorganization, Synaptic plasticity- synaptogenesis and dendritic growth
3. Specificity ( Task, Environment, Meaning)
4. Repetition matters
5. Intensity matters
Low intensity stimulation can cause Long Term Depression (LTD) as opposed to high intensity stimulation causing Long Term Potentiation (LTP). After brain injury it is possible to worsen function if overuse and attempt stimulation too early.
6. Time matters
Time necessary to allow plastic changes- gene expression, synapse formation, cortical reorganization. More time required after brain injury but there appear to be time-dependent sensitivity to the neural processes. Potential time windows for effectiveness following brain injury i.e. outcomes at 30 days vs 5 days post stroke
7. Salience matters
Rehabilitation task has to have meaning. Tasks that have attention and meaning drive neural processes which are critical for experience dependent plasticity. Sufficient motivation and attention critical. Task has to be relevant, novel and have meaning
8. Age matters
Neuroplastic responses, experience dependent potentiation, synaptogenesis and cortical map reorganization all reduces with aging. Effects differ in different individuals and generally better in those with greater physical and mental activity. Plastic changes still occur in older brains
9. Transference
Refers to ability of plasticity in one area can promote concurrent or subsequent plasticity. Training in one activity can enhance the acquisition of similar activities- i.e. teaching a bed to wheelchair transfer is not the same as teaching bed to toilet but one will help the other.
10. Interference plasticity
Learning to compensate can limit the ability for developing a different neural connection for the lost function. Sometimes we are really good compensators. And developing neural connections that help us compensate for lost function may actually interfere with the likelihood of developing a different neural connection related to that function.

Question 4

Discuss the terms redundancy and compensation

Answer 4

Redundancy: Undamaged brain regions are recruited; these areas generate commands to the same muscles as were used before the injury .
• Training allows the unmasking of redundant neurons, pre-existing cortico-cortical connections are facilitated
• Rehabilitation can shape subsequent recovery related re-organisation in adjacent intact cortex

Compensation: Alternate muscles can be used to accomplish the task goal. (Another way of achieving the movement) last resort