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اوه وال
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STRUCTURAL BASES OF FUNCTIONAL
RECOVERY
*Neuroblast Migration
* Angiogenesis
¢Axonal Sprouting and Regeneration
¢Specific Issues in Intracerebral Hemorrhage
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STRUCTURAL BASES OF FUNCTIONAL
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A myriad of evidence from animal experiments suggests that
neurogenesis does occur after stroke. Neuroblasts usually originate from their
source location in the brain, such as the subgranular zone in the dentate gyrus of
the hippocampus and the subventricular zone. In rodent stroke models,
neuroblasts divert from the rostral migratory system and move to the ischemic
penumbra. These migrated neuroblasts may replace injured neurons or glial cells,
and help with remodeling and reorganization processes . This has long been
considered a unique process in animals; however, recent evidence shows that
neuronal migration occurs in adult human brains as well. Brain biopsy and autopsy
studies in humans have shown that neurogenesis occurs after stroke . However, it
still remains to be elucidated whether the neurogenesis directly translates into
clinical functional benefit in the human brain.
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STRUCTURAL BASES OF FUNCTIONAL
RECOVER
Neuronal death after vascular occlusion is a major underlying pathophysiology of
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STRUCTURAL BASES OF FUNCTIONAL
RECOVER
Axonal sprouting and regeneration also
play a significant role in neurologic recovery. The major stimuli for this
process are thought to be peripheral deafferentation. Axonal sprouting is
mainly driven by the balance between a growth-promoting status and
reduction of growth-inhibitory environment. Axonal sprouting may alter
cortical sensory or motor maps, and robust evidence exists to show that
new connections are formed in peri-infarct cortex areas . Nogo-A protein is
closely related with this process. It limits plasticity via inhibiting neurite
outgrowth. AntiNogo-A antibody enhances functional recovery and
promotes reorganization of the corticospinal tract with axonal plasticity.
Therefore, it is currently a hot topic for modulating regeneration
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STRUCTURAL BASES OF FUNCTIONAL
RECOVER
In intracerebral hemorrhage,
extravasated blood forms a clot and generates thrombin which is a potent source
for post-hemorrhage inflammation. However, recent animal research shows that
thrombin might be important in the functional recovery process by stimulating
neuroblasts, enhancing neurogenesis, promoting secretion of nerve growth factors,
and affecting neurite outgrowth . Thrombin also enhances angiogenesis and
synaptic remodeling, and has a strong effect on brain plasticity. By contrast,
Hirudin, a specific inhibitor of thrombin, decreases neurogenesis in a rat
intracerebral hemorrhage model, suggesting the importance of thrombin in
neurogenesis. Moreover, statin has a pleiotropic effect, and has strong beneficial
effects on angiogenesis, neurogenesis and synaptogenesis in animal models.
However, this should be re-evaluated in prospective clinical trials.
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FUNCTIONAL CORTICAL REORGANIZATION
٠ Advanced functional imaging helps us understand the underlying
mechanisms of functional recovery from a neurologic deficit. The
suggested mechanisms of cortical functional reorganization are
peri-infarct reorganization, recruitment of ipsilesional or
contralesional cortex, changes in interhemispheric interactions, or
bihemispheric connectivity . Active rehabilitation treatment might
improve the neurologic deficit mediated by one of the above
mechanisms.
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FUNCTIONAL CORTICAL REORGANIZATION
Several functional imaging studies using SPECT or PET have demonstrated
that functionally connected but structurally distant brain regions acted suboptimally
after primary brain injury, which is called diaschisis . After the acute phase,
spontaneous neurologic recovery happens with the reversal of this type of functional
impairment. Therefore, reversal of diaschisis is one of the mechanisms of
spontaneous functional improvement. The most common form is crossed cerebellar
diaschisis which occurs in the contralateral cerebellum after hemispheric stroke,
mediated by the descending glutamatergic crossed corticopontocerebellar pathway. In
middle cerebral artery infarction, the degree of crossed cerebellar diaschisis is well
correlated with the neurologic deficit early after stroke . Moreover, functional
inhibition may occur ipsilaterally to the subcortical lesion (thalamocortical diaschisis),
which is regarded as an underlying mechanism of subcortical aphasia or neglect
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FUNCTIONAL CORTICAL REORGANIZATION
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showed that the representative hand areas in the motor cortex started to shrink after
lesioning, and the cortical areas representing elbow or shoulder expanded. Even in humans,
ipsilateral perilesional cortical activation including premotor or supplementary motor area is a
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at least in the acute period. Inhibition of those recruited areas using transcranial magnetic
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FUNCTIONAL CORTICAL REORGANIZATION
In the recovery phase, the corresponding area in the contralateral
cortex frequently shows coactivation. However, it is still debatable whether contralateral
cortical activation is beneficial. In patients with aphasia, the contralateral nondominant
hemisphere helps with neurologic recovery . Studies from aphasic patients showed that
cerebral blood flow was increased in the right inferior frontal lobe along with recovery. Other
studies showed bihemispheric temporal and frontal engagement in auditory verbal
processing during the recovery process. Meanwhile, a new balance in the cortical activation
is needed in the chronic stage. Therefore, a decrease in the activation in the contralateral
cortex is observed in patients with better functional recovery. Continuous coactivation of the
mirror cortex represents maladaptive cortical mapping, which is related with nonoptimal
functional recovery. The underlying mechanisms of change in contralateral cortical
activation share similar physiologic changes such as unmasking of latent synapse,
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FUNCTIONAL CORTICAL REORGANIZATION
. A growing number of
evidence supports that the contralesional (ipsilateral) motor cortex was
activated after stroke . Although the exact mechanism of coactivation of the
contralesional motortor cortex is still elusive, the disinhibition hypothesis is
the most widely accepted . With the development of hemispheric stroke,
interhemispheric transcallosal inhibition is decreased from the affected side,
which is translated into more activation of the contralesional motor cortex.
The potential descending motor pathway from the contralesional hemisphere
to the ipsilateral arm is via uncrossed ipsilateral descending corticospinal
fibers, or noncorticospinal fibers, which is the corticoreticular projection,
fibers passing through the red nucleus and pontine and olivary nucleus .
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FUNCTIONAL CORTICAL REORGANIZATION
* Generally, the neurologic outcome of the patients who recovered with
ipsilateral (contralesional) motor cortex activation is worse than of those who
recovered with perilesional reorganization . Moreover, those patients
experience mirror movements with recovery, which is attributed to the
ipsilateral motor pathway . The severity of mirror movements showed a
reverse correlation with hand motor function. Therefore, abnormal involuntary
mirror movement, or proximal-distal interjoint coupling may have a
detrimental effect on functional recovery. Even with these conflicting results,
the ipsilateral descending pyramidal tract helps trunk muscle recovery, and is
an important factor in motor recovery in children.
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FUNCTIONAL CORTICAL REORGANIZATION
¢In patients who recovered from unilateral
cerebellar infarction, it seems that the
cerebellocortical loop on the opposite side might
be important . When recovering from thalamic
infarction, a somatosensory gaiting process plays
a significant role in sensory improvement.
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PHARMACOLOGIC OPTIONS TARGETING
FUNCTIONAL IMPROVEMENT
* With the help of a sound understanding of the underlying mechanisms of the neurologic
recovery and neural plasticity, pharmacological and nonpharmacological approaches to
augment neurologic recovery were attempted.
۷ Amphetamine is a monoamine agonist which increases
norepinephrine, dopamine, and serotonin levels in the brain. Animal experimental studies
using rats and cats showed that administration of amphetamine concomitantly with motor
practice accelerated recovery from cortical injuries. Although amphetamine is a potent
psychomotor stimulator, this effect is thought to be independent of its psychostimulatory
effect, which is mediated by dopamine. Several human randomized clinical trials were
performed to identify the beneficial effect of amphetamine on neurologic recovery. Although
several anecdotal reports support that it may help a ‘speedy recovery’ in small numbers of
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PHARMACOLOGIC OPTIONS TARGETING
FUNCTIONAL IMPROVEMENT
Antidepressants may promote neuroplastic changes mediated
by surges of the amount of synaptic monoamines. Based on this, a pivotal
randomized controlled clinical trial was performed and the results were recently
published [30]. Patients treated with fluoxetine and physiotherapy showed
better distal motor power improvement and less dependency at 3 months,
compared with those with physiotherapy alone. Although the precise underlying
mechanisms are unknown, fluoxetine seems to be effective via modulating
brain plasticity. With the positive results, it is still unclear whether other
selective serotonin reuptake inhibitors have a similar effect on neurologic
recovery, or whether the routine use of fluoxetine is justifiable in patients
without post-stroke depression. More studies are needed.
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PHARMACOLOGIC OPTIONS TARGETING
FUNCTIONAL IMPROVEMENT
* Dopaminergics A randomized single-blind crossover trial was
done before using levodopa administration in the chronic stage of
stroke patients. Although the treated dose was low (100 mg per
day), the treatment group showed better motor performance at 5
weeks after treatment, and better cortical excitability measured
by repetitive transcranial magnetic stimulation . This study was
based on a small number of patients; therefore, it needs to be
verified in a larger study.
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NONPHARMACOLOGIC THERAPEUTIC OPTIONS
* Noninvasive Cortical Stimulation Repetitive transcranial magnetic
stimulation or transcranial direct current stimulation are
noninvasive cortical stimulation methods to modulate cortical
excitability in humans . These noninvasive cortical stimulation
techniques administered alone or in combination with various
methods of neurorehabilitation were reported to be safe in the
short term. However, more studies are needed to verify their
long-term effect on motor recovery
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NONPHARMACOLOGIC THERAPEUTIC OPTIONS
* Constraint-Induced Movement Therapy After severe motor stroke, patients
may preferentially use the nonaffected limbs. This pattern of movement
activates the contralesional hemisphere which may inhibit the damaged
hemisphere via interhemispheric transcallosal inhibition. Constraint-
induced movement therapy consists of forced use of the paretic arm
aiming to decrease transcallosal inhibition in the affected hemisphere.
Reduced unwanted inhibition improves the latent pathway and helps motor
recovery via unmasking of the latent pathway. With constraint-induced
movement therapy, expansion of ipsilesional motor maps with concomitant
decreases in contralesional motor cortex activation was observed, strongly
correlating with motor gains .
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* سیناپتوژنزیس رژنراتیو: جوانه زدن اکسون های آسیب دیده در تلاش برای
برقرارى ارتباط
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1.spontaneus recovery:
Diachisis or resolution of edema and
absorption of necrotic tissue (first 3- 4 week)
2.Functional induced recovery (neural
reorganization)
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¢ 2.Functional induced recovery (neural
reorganization)
¢ Vicariance:
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* Unmasking-sprouting (after 4 week)
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Reduction of cerebral edema
¢ Absorption of damaged tissue
¢ Improved local vascular flow
* Collateral sprouting
¢Unmasking of neuropathway
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¢ Initial return of movement in the first 2 weeks is
one indicator of the possibility of full arm recovery
* failure to recover grip strength before 24 days is
correlated with no recovery of arm function at 3
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*Flaccidity
*Spasticity
*Relative recovery
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1. Use it or lose it
The skills we don’t practice often get worse.
2. ولا 1] 500 ۱۳۵۳۵۷۵
The skills we practice get better
3. Specificity
We must practice the exact tasks we want to improve.
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We must do a task over and over again once we've got it right to
actually change the brain.
5. Intensity matters
More repetitions in a shorter time are necessary for creating new
connections in the brain.
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SUMMARY
* Here, we briefly reviewed the basic neurologic recovery
mechanisms after stroke. Modern functional imaging helped with
the understanding of basic mechanisms underlying functional
improvement; however, more studies are needed to better
understand the optimal mechanism in individual patients.
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منابعی برای مطالعه بیشتر
* O Sullivan, B. O, Schmitz T, Fulk G. D. Physical Rehabilitation, seventh edition,
Davis Co.
* Shumway cook A, Woollacott M H. Motor Control, translating research into
clinical practice, Fifth edition, Wolters Kluwer Company, 2017
* Sang-Bae Ko, Byung-Woo, Mechanisms of Functional Recovery after Stroke,
Naritomi H, Krieger DW (eds): Clinical Recovery from CNS Damage. Front Neurol
Neurosci. Basel, Karger, 2013, vol 32, pp 1-8 (DOI: 10.1159/000346405)
* Nudo RJ: Neural bases of recovery after brain injury. ) Commun Disord 2011;
44:515-520