Questions: Brain Plasticity and Recovery After Injury

Question 1

Six months after a stroke affecting left motor cortex, Patient A shows predominantly left perilesional activation during hand movements. Patient B shows strongly bilateral activation (both hemispheres active). Which patient likely has better motor function?

• A. Patient A — perilesional recovery is more efficient and indicates fuller functional takeover by surviving tissue
• B. Patient B — bilateral engagement shows the brain is using maximum resources to compensate
• C. They are likely similar — both patterns indicate successful neural reorganization
• D. Patient B — recruiting both hemispheres doubles the available processing power for movement

Answer: (A)

Greater bilateral activation in chronic stroke survivors correlates with poorer outcomes. When perilesional cortex fully assumes the lost function, activation is predominantly lateralized to the recovering hemisphere. Contralesional recruitment provides partial but suboptimal substitution — the right hemisphere homologues of motor areas can partially take over, but the result is less efficient. Bilateral activation therefore signals that the preferred perilesional mechanism is incomplete, not that the brain is deploying more resources successfully.

Question 2

Two post-stroke rehabilitation protocols are compared: (1) passive massage and gentle range-of-motion exercises 30 min/day; (2) constraint-induced movement therapy (CIMT), immobilizing the unaffected arm and forcing 6+ hours of daily task use of the impaired arm. Which is more effective and why?

• A. Protocol 2 — intensive, task-specific use of the impaired limb drives perilesional reorganization through experience-dependent plasticity
• B. Protocol 1 — gentle stimulation avoids overloading damaged circuits and allows natural recovery processes to proceed
• C. They are equivalent — the key variable is time since stroke, not therapy intensity
• D. Protocol 2 — but only because immobilizing the good arm weakens it, making the impaired arm seem more functional by comparison

Answer: (A)

CIMT works because cortical reorganization is proportional to how much recovering circuits are actually used. Intensive, task-specific use of the impaired limb drives perilesional motor cortex to expand its representations and form new synaptic connections — the same experience-dependent plasticity that explains map expansion in musicians. Passive treatment generates insufficient neural activation to drive reorganization. Low dosage or passive approaches consistently produce worse outcomes than intensive, ecologically valid protocols.

Question 3

After a stroke, lost neurons in the infarcted core cannot regenerate; functional recovery therefore requires reorganization of surviving neural tissue.

• T. True
• F. False

Answer: True

This is the foundational constraint on recovery: unlike peripheral nerves, neurons in the CNS do not regenerate after infarction. The infarcted core is permanently lost. Recovery must work through perilesional reorganization (surviving tissue adjacent to the lesion assuming lost functions) and contralesional recruitment (opposite hemisphere homologues partially substituting). Understanding this constraint is what makes intensive rehabilitation essential — you cannot restore what's gone, only reorganize what remains.

Question 4

Bilateral cortical activation during a motor task is a reliable sign of strong, complete recovery in chronic stroke survivors.

• T. True
• F. False

Answer: False

Neuroimaging evidence shows the opposite: in chronic stroke survivors, bilateral activation during motor tasks correlates with residual impairment and poorer performance, not better recovery. When perilesional cortex fully assumes the function, activation patterns are predominantly lateralized (ipsilesional). Bilateral activation reflects incomplete perilesional recovery and dependence on contralesional substitution — a less efficient backup system. It indicates the brain is working harder to produce impaired performance, not evidence of fuller compensation.

Question 5

Why does constraint-induced movement therapy (CIMT) produce better recovery outcomes than passive rehabilitation, and what principle of neural organization explains this?

Model answer: CIMT forces intensive use of the impaired limb by making it the only tool available for daily activities. This drives sustained activation of perilesional motor cortex circuits — exactly the experience-dependent plasticity mechanism that expands cortical representations in proportion to use. Passive treatment or gentle exercises generate insufficient circuit activation to drive reorganization. The core principle is that cortical maps reorganize in proportion to how heavily they are used: the brain cannot reorganize toward function that is not being practiced.

The principle at work is experience-dependent plasticity — the same mechanism that produces enlarged finger representations in string musicians. Applied to recovery: perilesional cortex can assume lost functions, but only if driven by intensive, task-specific activation. CIMT creates this activation by eliminating compensatory strategies (using the good arm). Rehabilitation that is low-dosage, passive, or delayed capitalizes on plasticity far less effectively, producing substantially worse recovery at the same post-stroke timepoint.