BASIC · EP 08 · CNS
Before You Listen
Episode Setup
- Topic in one line: Part 2 of BASIC-08 covers the system-level half of the CNS recovery curriculum: the three patterns of cortical reorganization after focal injury (perilesional, contralesional, diaschisis), the Kleim and Jones ten principles of experience-dependent plasticity, the constraint-induced movement therapy (CIMT) protocol that operationalizes intensity and task specificity, the pharmacology that enhances recovery (amantadine, methylphenidate, modafinil) versus impairs it (benzodiazepines, typical antipsychotics, chronic phenytoin), and the maladaptive plasticity that drives phantom limb pain, central neuropathic pain, and spasticity.
- Prerequisites: the cellular plasticity material from BASIC-08 Part 1 (Hebbian principle, long-term potentiation (LTP), long-term depression (LTD), unmasking, collateral sprouting), the Brunnstrom stages of motor recovery, the Modified Ashworth Scale, the major motor cortex maps, and the role of dopamine in motivation and reward.
- Runtime: approximately 30 minutes.
Vignette. A 58-year-old right-handed woman is 6 weeks out from a left middle cerebral artery (MCA) ischemic stroke that left her with right hemiparesis. She has 15 degrees of active wrist extension, 25 degrees of active finger extension, and Modified Ashworth Scale 1+ in the wrist flexors. She is independent with bed mobility and stand-pivot transfers. Her speech is fluent. She is highly motivated and has good family support. Her prior medications include lisinopril, atorvastatin, aspirin, and clopidogrel. The inpatient rehabilitation team is considering constraint-induced movement therapy (CIMT) and discussing whether a benzodiazepine should be added for situational anxiety, whether a selective serotonin reuptake inhibitor (SSRI) is indicated to enhance recovery, and what therapy intensity is supported by the evidence.
Does she meet the upper extremity criteria for CIMT, what is the standard CIMT protocol, why are benzodiazepines specifically problematic during her current recovery window, what does the most recent evidence (FOCUS, AFFINITY, EFFECTS trials) say about prescribing fluoxetine for motor recovery alone, and approximately how many therapy repetitions per session does the basic-science literature suggest are needed to drive cortical reorganization?
(Answer at the end of this chapter)
Section 2: Cortical Reorganization After Injury
Bottom line: after focal CNS injury, three reorganization patterns dominate. Perilesional reorganization is the functional takeover of lost cortical territory by immediately adjacent surviving cortex and is the form most strongly correlated with motor recovery (Nudo squirrel monkey studies, 1996). Contralesional recruitment is increased activation of the uninjured hemisphere; the interhemispheric competition model frames this as adaptive in the early phase but maladaptive if persistent, providing the rationale for CIMT and non-invasive brain stimulation. Diaschisis is depression of activity in regions distant from but functionally connected to the lesion; its reversal accounts for some of the early spontaneous recovery seen in the first weeks. Recovery proceeds through three phases: acute (days; edema resolution, reperfusion, unmasking), subacute (weeks to 3-6 months; perilesional sprouting and cortical reorganization, the maximal plasticity window), and chronic (beyond 3-6 months; ongoing slower plasticity and behavioral compensation).
After focal CNS injury, the cortical map of the affected body part undergoes reorganization that is visible on transcranial magnetic stimulation (TMS) mapping, functional magnetic resonance imaging (fMRI), and positron emission tomography (PET). Three reorganization patterns emerge, and each carries a different implication for therapy design.
Perilesional reorganization is the functional takeover of lost cortical territory by immediately adjacent surviving cortex. In the somatosensory and motor cortices, the representation of the affected body part progressively expands from neighboring face or arm representations into the denervated territory over weeks to months. This is the most beneficial form of cortical plasticity and the primary structural substrate for motor recovery after stroke. Animal studies by Nudo and colleagues (1996) demonstrated that after experimental cortical infarcts in squirrel monkeys, spontaneous perilesional reorganization was minimal and the infarct territory actually expanded into surrounding cortex. When animals received intensive, repetitive motor training of the affected limb, perilesional cortex was preserved and even expanded its representation. These findings provided the neurobiological rationale for intensive task-specific rehabilitation after stroke.
Source: Pancrat, Wikimedia Commons (after Penfield & Rasmussen 1950), via Wikimedia Commons, CC BY-SA 4.0. https://commons.wikimedia.org/wiki/File:Motor_homunculus.svg Contralesional recruitment is increased activation of the uninjured hemisphere during attempted movement of the affected limb, demonstrated on functional imaging studies. The ipsilateral motor pathways from the uninjured hemisphere (the uncrossed anterior corticospinal tract and the corticoreticulospinal pathways) can contribute to motor output to the affected side. The functional significance is debated. The interhemispheric competition model (Murase et al., 2004) holds that the two motor cortices normally exert mutual inhibition through transcallosal pathways. After unilateral injury, the damaged hemisphere loses its inhibitory influence on the contralesional hemisphere, producing excessive contralesional activity that paradoxically suppresses the residual ipsilesional motor cortex. In this framework, contralesional recruitment is adaptive in the early phase (compensating for severely reduced ipsilesional output) but becomes maladaptive if persistent, preventing optimal ipsilesional recovery. This model provides the neurobiological rationale for CIMT and for non-invasive brain stimulation protocols (TMS, transcranial direct current stimulation (tDCS)) that suppress contralesional overactivity and enhance ipsilesional excitability.
Diaschisis is depression of activity in regions distant from but functionally connected to the lesion. Examples include a thalamic infarct producing depressed cortical activity, a cortical infarct producing depressed cerebellar activity through the corticopontocerebellar pathway, and a cerebellar lesion producing crossed cerebellar diaschisis in the contralateral cortex. Reversal of diaschisis (resolution of edema, recovery of remote function over the first weeks) accounts for some of the early spontaneous recovery and explains why some neurologic deficits resolve more rapidly than the underlying injury would suggest.
Recovery proceeds through three phases. The acute phase (days) reflects edema resolution, reperfusion of viable penumbra, reversal of diaschisis, and unmasking of latent pathways. The subacute phase (weeks to 3-6 months) is dominated by perilesional sprouting and cortical reorganization, and represents the maximal plasticity window. The chronic phase (beyond 3-6 months) features ongoing but slower plasticity and behavioral compensation. The proportional recovery rule (Prabhakaran et al., 2008) suggests that approximately 70 percent of patients recover a fixed proportion (about 70 percent) of their maximum potential motor deficit within the first 3 months post-stroke, although this rule does not apply to patients with severe injuries or extensive corticospinal tract damage. The rule does not mean that recovery ceases after 3 months. Plasticity continues indefinitely, and meaningful functional gains can be achieved in the chronic phase with sufficient intensity of practice; the EXCITE trial enrolled patients 3-9 months post-stroke and still demonstrated significant gains with CIMT.
High Yield — Cortical reorganization after injury
- Perilesional reorganization: takeover of lost territory by adjacent cortex; correlates with motor recovery; driven by intensive task-specific practice (Nudo squirrel monkey studies, 1996).
- Contralesional recruitment: ipsilateral motor pathways from uninjured hemisphere; adaptive early, maladaptive if persistent (interhemispheric competition model, Murase 2004); rationale for CIMT, TMS, tDCS.
- Diaschisis: depression of activity in regions distant from but functionally connected to the lesion; reversal contributes to early spontaneous recovery.
- Three phases: acute (days, edema/reperfusion/unmasking), subacute (weeks to 3-6 months, maximal plasticity window, perilesional sprouting), chronic (beyond 3-6 months, ongoing slower plasticity plus behavioral compensation).
- Proportional recovery rule (Prabhakaran 2008): approximately 70 percent of patients recover ~70 percent of their maximum potential motor deficit in the first 3 months; does not apply to severe injuries with extensive corticospinal tract damage.
- Recovery does not stop at 3 months — chronic-phase gains achievable with sufficient intensity (EXCITE trial enrolled 3-9 months post-stroke).
Board Trap — “Recovery plateau means therapy should stop”
A vignette describes a stroke patient at 4 months post-event whose motor function appears to have plateaued; the family asks whether outpatient therapy should be discontinued. The trap is to conclude that the plasticity window has closed. Plasticity continues indefinitely, and chronic-phase gains require sufficient intensity of practice. The EXCITE trial enrolled patients 3-9 months post-stroke and demonstrated significant gains with CIMT. The correct response is to confirm whether the patient has the residual motor capacity to participate in intensive practice (10 degrees active wrist extension, 20 degrees active finger extension for upper extremity CIMT) and to escalate intensity if so, rather than withdraw therapy.