keywords: stroke rehabilitation myelin
“Someday we’ll find it, the rainbow connection, the lovers, the dreamers, and me.” — Kermit the Frog, 1979
There is an image that captures something the standard account of stroke recovery cannot quite reach.
A rainbow is not two separate arcs. It is one continuous arc, and we perceive it as such even when cloud or hill obscures the middle section. We see the colours rising on the left and the colours descending on the right and we know, without calculating, that they belong to the same bow. The arc completes itself in our perception even when it cannot complete itself in the sky.
Stroke, viewed through the Myelin Mind thesis, is a broken rainbow. The arc exists at both ends. The colours are still there. What the lesion has destroyed is not the intention or the capacity but the connection between them. The task of rehabilitation is not to paint a new rainbow. It is to rebuild the bridge across the gap so the existing arc can complete itself.
The intentional arc
Maurice Merleau-Ponty described what he called the intentional arc: the prereflective trajectory that connects the body’s sense of what it wants to do with its capacity to do it. This is not a conscious process. You do not decide to reach for a cup and then instruct your arm to move. The wanting and the doing are continuous, a single arc from intention to action, from vouloir to pouvoir, from wanting to being able.
This arc is not located in the brain alone. It runs through the whole body, through the myelinated pathways of the peripheral nervous system that constitute what Merleau-Ponty called the body schema: the body’s prereflective knowledge of its own capacities and position in space. When you reach for a cup, the arc involves your visual system, your motor cortex, your spinal cord, the myelinated peripheral nerves of your arm, your hand, your fingers. It is a distributed, embodied trajectory, and it flows continuously when the myelinated structure is intact.
Stroke breaks this arc. Not at both ends, but in the middle. The vouloir end persists: the patient knows what they want to do, the intention is intact, the desire to reach is real. The pouvoir end also persists: the peripheral myelinated pathways in the arm, the hand, the fingers, the decades of accumulated motor habit inscribed in white matter throughout the body, are untouched by the cerebral lesion. What the stroke has destroyed is the central connection between them. The arc exists at both ends. The middle has collapsed.
This is why stroke is so particular in its cruelty. The patient wants to speak and cannot. Wants to move their hand and cannot. The wanting is vivid and intact. The capacity is there, waiting, in the myelinated structure of the peripheral nervous system. But the connection is gone. The rainbow is broken.
The biology of the gap
The previous article in this series described the three-stage process by which stroke recovery proceeds at the biological level. Inhibitory myelin proteins must be suppressed to allow axon sprouting in the peri-infarct zone. Astrocytes provide the scaffold along which new axonal pathways can be routed. Intense neural activity then triggers astrocytes to shuttle lactate, which is simultaneously the fuel for active axons and the building block of myelin synthesis, and the signal that recruits oligodendrocytes to remyelinate the new pathways.
The final stage of this process, remyelination by oligodendrocytes, is what Deleuze would recognise as the first passive synthesis of time: the contraction of habit. Not time itself but the biological condition for habituated time, for the body that knows how to do things without thinking. Myelination is the material substrate of habitus. The stroke ruptures this substrate at the level of the central pathways. Rehabilitation is the process of reconstituting it.
Current rehabilitation drives this process through repetition. The patient repeats the lost movement, again and again, generating the neural activity that drives the lactate signal, recruiting oligodendrocytes to the rerouted pathways. The repetition works. The biological logic is sound.
But something is missing.
The problem with bare repetition
Clinicians have long observed that rehabilitation works better when it has meaningful context. A patient recovering arm function after stroke improves faster when reaching for a real object they actually want than when performing the same movement as an abstract exercise. The movement is identical. The neural pathway recruited is the same. But the outcome differs.
The standard account has no good explanation for this. If rehabilitation is motor learning, and motor learning is synaptic strengthening, then the meaning of the movement should be irrelevant to its neurological effect. A repetition is a repetition.
Deleuze’s account of repetition suggests otherwise. Bare repetition, the same movement performed for its own sake, does not produce the same thing as repetition with difference, repetition that is going somewhere, that completes something, that means something. The first passive synthesis, the contraction of habit, is not built from bare repetition. It is built from repetition that has a trajectory, that pulls toward a future, that anticipates.
This is where the intentional arc and the biology of myelination converge.
The animator’s insight
Henri Bergson wrote about grace as the felt quality of movement that flows naturally toward its completion, movement that the observer can anticipate before it arrives. The great animators formalised this intuition in what they called the spacing and timing chart: the precise distribution of an object’s positions across frames that gives the observer the felt sense of where the movement is going.
When an animator places an object at point A, then B, then C, with the right spacing and timing, something happens in the observer’s nervous system. They do not calculate where D will be. They feel it coming. The intentional arc completes itself in the observer’s body before the object arrives. This is not intellectual prediction. It is the prereflective anticipation that Merleau-Ponty described, the vouloir end of the arc engaging before the pouvoir end is required.
The proposal the Myelin Mind thesis generates is this: use this felt anticipation as the scaffold for stroke rehabilitation.
Instead of asking the patient to perform a meaningless repetition, give them a trajectory to complete. Show them a movement: A to B to C, with spacing and timing that carries the Bergsonian quality of grace, that makes D feel inevitable, felt, wanted. The vouloir end of the broken arc is intact. The patient’s nervous system will reach toward D not as an exercise but as the completion of a perceived intention in space. The repetition that follows is not bare repetition. It is repetition with difference, in the Deleuzian sense: repetition that produces something, that completes something, that the nervous system recognises as meaningful.
The biological consequence follows from the lactate argument. Meaningful, directed neural activity, activity that is reaching for something real, drives a stronger and more targeted lactate signal than mechanical repetition. Oligodendrocyte recruitment follows the active pathways. The pathways that are most active are the ones most urgently reaching toward completion. Meaningful rehabilitation does not just feel better. It is, on this account, biologically more effective.
A new logic of rehabilitation
This proposal does not replace the three-stage biological protocol described in the previous article. It supplements it. The suppression of inhibitory myelin proteins creates the conditions for axon sprouting. The astrocyte scaffold routes the new pathways. The lactate signal recruits the oligodendrocytes. Rehabilitation drives the lactate signal.
What the intentional arc argument adds is a principle for the design of rehabilitation itself. The repetition should not be bare. It should be the completion of a felt trajectory. The patient should be reaching for D, not performing movement for its own sake.
In practical terms, this suggests a rehabilitation approach built around mixed reality: a headset that combines a real world camera with a virtual overlay, so that the patient sees their actual environment, their actual hand, their actual body, while a virtual object moves through that real space with Bergsonian grace.
The virtual object traces a path: A to B to C, with spacing and timing that carries the felt quality of anticipated movement, that makes D inevitable before it arrives. The virtual object slows at D, or implies arrival, and the patient reaches with their real, recovering hand to catch it in real space. The vouloir end of the arc is engaged by the felt trajectory of the virtual object. The pouvoir end is engaged by the real physical reach. The mixed reality environment is the bridge across the broken rainbow, virtual intention meeting real capacity in the space where the connection needs to be rebuilt.
The choice of mixed reality rather than pure virtual reality is not incidental. In a fully virtual environment the patient reaches into a simulation. In mixed reality they reach into their actual world with their actual hand. The embodiment is real. The arc completes in the world, not in a representation of it. The cup may be virtual but the reaching is not, and it is the reaching that drives the lactate signal, recruits the oligodendrocytes, and rebuilds the myelinated pathway.
This is a testable hypothesis. The prediction is specific: mixed reality rehabilitation designed around projected trajectories with Bergsonian spacing and timing will produce faster and more durable recovery of motor function after stroke than equivalent repetition without projected trajectory, because it drives more intense and more targeted neural activity along the recovering pathways, generating a stronger lactate signal and more efficient oligodendrocyte recruitment. The measurement is the recovery. The therapy is the test.
The hardware to run this experiment exists today, off the shelf. The Meta Quest 3 and similar mixed reality headsets already incorporate markerless hand tracking using onboard cameras, allowing the patient’s bare hand to move and grasp naturally within the mixed reality environment without a controller or instrumented glove. The hand is free. The reach is real. The grasp completes the arc without the interposition of any tool between intention and world. For finer grip and force sensing in later trial phases, thin stretchable sensor gloves or single-ring trackers are already in development and clinical validation. But the core protocol requires nothing that does not already exist. The experiment is not waiting for technology. It is waiting for a trial.
The rainbow does not need to be repainted. It needs a bridge, built from the patient’s own anticipation, across the collapsed middle section, so that the arc that exists at both ends can finally complete itself. The virtual cup traces the path. The real hand completes it.
Jack Parry is a philosopher and biomedical animator at Swinburne University of Technology. He is the author of The Myelin Mind: The Genesis of Meaning.A longer academic treatment of this argument is in preparation.