Motor learning is what everyone does to learn any new movement. Motor relearning is what stroke survivors do to recover any lost movement. In some ways learning movement and relearning movement after stroke are the same; they both rely on the neurons in the brain to control movement. In some ways learning and relearning a movement are inherently different because a new and different part of the brain is used to control the movement. And there is a more obvious and less science-heavy difference: Learning a movement is fun. Relearning a movement is fraught with frustration.
Motor Learning And Motor Relearning: The Differences.
For stroke survivors, the part of the
brain that was used their entire lives to control particular movements is dead.
The dead portion of the brain becomes a fluid-filled cavity (called an infarct). Some of the neurons used in the pre-stroke movement may be reengaged. But those neurons will have to create novel relationships with other neurons to recover the pre-stroke movement. There is no potential to relearn a movement in the same way it was originally
learned.
Motor relearning after stroke has another distinction from motor
learning. Most motor learning that we do is derived from play. The joy of
learning a new skill propels us the development of that skill. Consider skiing.
You start out and you fall (and fall and fall) and you get very wet and very
cold. And then you do something right and that feeling of making the turn and
carving the snow becomes the carrot at the end of the motor learning stick. But
stroke survivors are not learning new skills; they’re simply relearning
movements that they used to do perfectly well as they attempt to cajole new
neurons to do old tricks. Where’s the fun in that?
The fact that motor relearning is not
necessarily fun provides a supreme challenge to the coaching abilities and
motivational skills of therapists as they shepherd stroke survivors, not towards
the joy of playful motor learning, but towards the monumental task of motor
relearning.
Motor
Learning And Motor Relearning: The similarities.
In some ways relearning to move after
stroke and “regular” motor learning are similar. Both require neuroplastic
rewiring of the motor and sensory portions of the brain. Both types of learning
require the learner to do the hard work (or play) of learning. No therapist, no
matter how talented, can learn it for them. This is where the coaching skills
of clinicians are tested. Motor relearning only happens if the stroke survivor
remains motivated to move. And stroke survivors will only remain motivated if
they know why they're doing what they're doing. The neuroscience is clear: only
through the volitional movement of the
stroke survivor does neuroplastic brain rewiring take place. Providing
stroke survivors with a nervous system “user’s manual” complete with
“instructions” and even “troubleshooting tips” is vital to the process of recovery.
And just like any good manual, the simpler the better.
Motor
learning simplified
Therapists usually think about the
nervous system in terms of upper motor neuron vs. lower motor neuron, brain vs.
spinal cord or central nervous system vs. peripheral nervous system. There is
another way to view the part of the nervous system that impacts motor learning:
front vs. back.
Consider the following thought experiment.
You decide you will scratch your head, but you don’t want to mess up your hair,
so you need a single nail to fall on the exact epicenter of itchiness. You begin
by estimating where your arm and hand is in space (proprioception). Messages
from the muscle spindles, Golgi tendon organs and other proprioceptors provide the
feeling of the position of the hand and arm. That feeling becomes a sensory
impulse that enters the back (dorsal root) of the spinal cord. The impulse
travels up the spinal cord and ends up in the back of the brain, in the sensory
portion of the cortex, just behind the central sulcus, a large fissure that separates
the front of the brain from the back. The impulse, with “fine-tuning” by other
parts of the brain, jumps to the anterior portion of brain and provides a
movement strategy. These instructions descend the spinal cord and exit the front
of the spinal cord. The impulse then goes into peripheral nerves which
terminate at the target muscles that power the movement. To review:
The
impulse goes from the proprioceptors in the limb
toàthe back of the spinal cord
toà the back of the brain
toà the front of the brain
andà out the front of the spinal cord.
toàthe back of the spinal cord
toà the back of the brain
toà the front of the brain
andà out the front of the spinal cord.
Back to front. You scratch your head. But
let’s say you miss your target and your nails land in the wrong place. You use this
feedback to self-correct and you again send an impulse from the back to the
front of your nervous system. Your nails target the exact point of itchiness. The
adjustment that you’ve made is the essence of motor learning. In this thought
experiment each attempt was felt and each feeling was used to mitigate the next
attempt.
Now let's continue the thought
experiment with a more complicated movement. Consider typing. Typing involves
precise and delicate movements of the fingers. Learning how to type involves
feeling the position of the fingers (proprioceptive input) followed by repeated
attempts to hit the correct keys on the keyboard (motor output). Each time the
pinky finger makes a foray towards the “enter” key the feeling of a correct
attempt is processed by the brain. If enough repeated attempts are successful,
the movement is learned. If the learned movement is done over weeks or months
or years, it is seared as a neuronal pathway into the brain. This is why we
never forget how to ride a bike or swim even if we haven't done either in
years. The motor strategies are “hardwired”. Hardwiring useful patterns of
movement in stroke survivors is motor relearning.
