Recovery from stroke and spinal cord injury

Question 1

Outline the corticospinal tract

Answer 1

Also known as the pyramidal tract: largely originates from M1 and is responsible for voluntary movement.

Axons from the cortex travel to the brainstem where 90% of them decussate.
When reach spinal cord level contact neurons in the ventral horn (interneurons and motor neurons)
Neurons in ventral horn go on to connect to muscles.

In SCI this is damaged, in stroke m1 is damaged.

Question 2

What is recovery of function after stroke thought to be down to?

Answer 2

Plasticity…there are 2 different ways this could happen. Not well understood.
1)Cortical reorganisation and 10% of the ipsilateral side.
2) Due to contralateral side of the body.

Question 3

What are the 2 different phases of recovery and how do they differ?

Answer 3

1) Acute: up to 12 weeks (or 6 months) after injury with 4 weeks the greatest abililty to recover function.
* There are neurotrophins that enhance plasticity and survival of neurons in this phase.
2) Chronic: In general where patients reach plateau in recovery of function. Occurs at around 6 months after injury.

Question 4

How does recovery of function compare to normal motor function?

Answer 4

Full motor function not regained. In particular fractionation of fingers etc.

Question 5

What is the ARAT?

Answer 5

Action Research Arm Test
Motor test: : Assesses a patient’s ability to handle objects differing in size, weight and shape and therefore can be considered to be an arm-specific measure of activity limitation.

Question 6

Outline Fugl Meyer Assessment

Answer 6

initial severity of upper limb Paresis is the best predictor of good functional outcome.
STROKE SPECIFIC: motor function, sensation, pain
*higher score = better function

The FMA at 30 days explained 86% of the variance at six months
You can actually predict what would be the recovery at 6 months based on the first 30 days
Because nothing happened after 30 days

Question 7

Outline the proportional recovery rule

Answer 7

Biological recovery (Δ FMA): change in impairments in the FMA from the first three days post stroke to 3 months later
ΔFMA-UEpredicted = 0.7·(66 − FMA-UEinitial) + 0.4

What does this imply?: recovery is spontaneous and current interventions do nothing.

Question 8

Compensatory strategies

Answer 8

As recovery for stroke patients is not complete compensatory strategies have been developed and even some physical therapy teaches this.

Somewhat controversial as tells patients that they can never recover function. On the other hand, chronic patients need to perform tasks so functional more important than performing movemments the ‘correct’.

1980’s when switch occurred, before that daily living was not taken into account and more focus on normal muscle tone and correct reflexes.

Question 9

Outline motor learning.

Answer 9

motor learning is the core idea that drives current task based approaches to neural rehabilitation as well as robotic and constraint based therapies in chronic stroke.
Statement: recovery after stroke is a form of learning or relearning.
The relearning rests on three assumptions
That the target to be rehabilitated has been properly identified
That a framework exists for choosing the proper learning mechanism
That learning mechanisms are intact in patients with stroke

NB: assumptions are likely to be untrue which makes statement untrue.

Question 10

Outline Instruction and imitation.

Answer 10

Form of motor learning.
1st there was a big emphasis on the adaptation tasks
However it is obvious that motor skills like cooking driving cannot be acquired without instruction or knowledge
Subjects cannot learn motor tasks with even minimal redundant structure without explicit instruction
Motor learning is not synonymous with low level automatic implicit processes.

Question 11

Outline reinforcement learning

Answer 11

Actions will be selected with increased or decreased frequency depending on the schedule of rewards and punishments, respectively.
The balance between present and future rewards is of central importance to reinforcement learning.
Constraint induced movement therapy(CIMT) is based on ideas from reinforcement learning. The good arm is constrained in an attempt to prevent adoption of the bad habits.
Reinforcement learning is also used as an attempt to train out of synergy movements in patients for example to decouple muscles involved in the flexor synergy after stroke.

Question 12

Outline sensorimotor adaptation.

Answer 12

Adaptation refers to reduction of errors in response to a perturbation.
This is a form of supervised learning with the goal of minimising the error between prediction and observations.
The relevance of sensorimotor adaptation to rehabilitation protocols remains unclear: changes in behaviour do not seem to last once the perturbation is removed.
For example in an experiment using a split belt treadmill to reduce step asymmetry in hemiparetic gaits the desirable after effects are very short lived.

NB: glasses experiment.

Question 13

Outline use dependent plasticity.

Answer 13

Neural changes induced via repetition of movements.
Behavioural consequences referred to as use dependent learning.

Question 14

Link between learning and plasticity

Answer 14

Learning implies plastic change.
Plastic change does not imply learning.

Question 15

UDP and voluntary movement.

Answer 15

In this experiment transcranial magnetic stimulation of the motor cortex was used to evoke isolated and directionally consistent thumb movements.
Subjects were then required to practise thumb movements for 30 minutes in the direction approximately opposite to the elicited by TMS .
The critical finding was that subsequent TMS was found to evoke movements in the direction practised rather than in the pre training baseline direction .
This is very interesting with regard of how movement repetition can lead to changes in cortical representation.

Question 16

Outline motor sequence learning

Answer 16

Motor sequence learning refers to the process in which a predetermined ordered lists (sequence) of motor actions is performed with increasing spatial and temporal accuracy.
Explicit and implicit motor learning are fundamental concepts for the understanding of sequence learning.
The differentiation is mainly based on awareness of the learned skill.
While explicit learning requires active attention and some form of rules that can be stated
Implicit motor learning takes place without awareness and in the absence of verbal knowledge of the performed motor task.

Question 17

Implicit vs explicit sequence learning

Answer 17

The classic example of implicit motor learning is to learn to walk as a child or to ride a bicycle. Accomplished without instructions. Learned skills are retrieved from implicit memory. However, some authors object that implicit learning also comes along with conscious inputs, which then lead to unconscious implications that are learned.
Explicit motor learning is defined “learning which generates verbal knowledge of movement performance (e.g., facts and rules), involves cognitive stages within the learning process and is dependent on working memory involvement”: learning dance steps.

Question 18

How is sequence learning measured?

Answer 18

The most commonly used method to examine motor sequence learning is the serial reaction time task (SRTT)
Participants receive visual stimuli (cues) appearing at different locations on a screen.
The participants are asked to respond to each cue by pressing the correct button as fast as possible. The time between cue presentation and motor response defines the reaction time. A decrease in reaction time is considered learning.

Question 19

Enriched environments.

Answer 19

In animal studies it has been shown that enriched environments promote motor recovery in animal models
how can one apply the principle of enrichments to patients
video games and virtual reality experiences have the potential to create more immersive, stimulating and mood enhancing experiences than conventional therapy

Enrichment consisted of four to six animals being housed in large wire-mesh cages filled with a variety of objects intended to stimulate general (bimanual) limb use.
Animals were exposed for 6 hr per day (5 d per week) to a Plexiglas reaching apparatus filled with highly palatable mini M&Ms (M&M/Mars, Hackettstown, NJ) used to encourage (rather than force) coordinated use of the impaired forelimb. The design of the apparatus prevented retrieval of pellets with the “good” limb.

Question 20

Video games

Answer 20

Video games also offer the possibility for general aesthetic enhancement of the clinical environment and may provide the opportunity for multiplayer interpersonal engagement
Patients spend a lot of time in their rooms alone or with bored relatives and friends
Making clinical and home environments more stimulating and encouraging motor activity even outside of therapy.
The mechanisms of enrichment are not known precisely but they likely work through promoting more time on task, adding task variety increasingly gain on skill learning and retention through the provision of reward perhaps mediated through dopamine

Question 21

Increased plasticity after injury?

Answer 21

Recovery due in part to increase of neurotrophic factors present after injury, increases chance of plasticity and survival of new neurons.
NB: not all plasticity is good plasticity.
Krakauer et al., 2016: showed that induced stroke after initial stroke able to restore function.

Question 22

Extra reading: motor learning.

Answer 22

Sanders et al., 2022: MusicGlove device, thousands of movements thought to be necessary to cause plastic changes. This cannot be achieved in clinic so often sent home with paper to follow.
Wearable device that is linked to computer.
Participants perform grasping movements, according to scrolling music notes. This group had better functional improvement and greater number of grasps than control.
Enriched matters.