Data for this review were identified by searches of peer‐reviewed journals with the terms “CNS plasticity”, “stroke”, “brain reorganisation”, “MEG”, “TMS”, “fMRI”, “PET”, “post-stroke recovery”, and “stroke rehabilitation”. Relevant findings from the authors' own studies are included.
ReviewPost-stroke plastic reorganisation in the adult brain
Section snippets
Physiology of sensorimotor brain areas and of related plasticity
The primary sensory and motor cortices, visual cortices, and secondary sensorimotor areas are all involved in sensory perception. The basal ganglia and thalamic‐relay circuits contribute to motor planning, perception, and sensorimotor integration. The supplementary motor and premotor cortices are essential for motor preparation and execution, the latter being implemented by corticospinal fibres from the primary motor cortex under the parallel control of other descending systems. Cerebellar
Physiology of motor plasticity
The extent to which neuronal sprouting—or the unmasking of existing, but functionally silent, synapses—is involved in reshaping motor output during learning or after a lesion is debatable. Changes in synaptic efficiency, such as long‐term depression and long‐term potentiation, significantly affect the extent of inhibition or excitation. These basic mechanisms underlie learning and memory as well as cortical plasticity. Long‐term potentiation is the prototype of modified synaptic efficacy;37 it
Neurophysiology of post‐stroke recovery
Several factors may contribute to brain reorganisation after stroke—e.g., changes in neuronal‐membrane excitability, removal of inhibition, improved synaptic transmission (possibly due to long‐term potentiation), loss of perilesional GABAergic inhibition (possibly associated with downregulation of GABAA receptors), and increased glutamatergic activity.45, 46, 55 After partial damage of the primary motor cortex in animal models,3 or after partial infarction of primary sensory and motor cortices
Techniques for functional brain imaging
Various imaging techniques are currently available; they either map regional blood flow and metabolic changes linked with neuronal firing (eg, PET and functional MRI [fMRI]) or analyse electromagnetic brain activity (eg, electroencephalography, magnetoencephalography, and trans‐cranial magnetic stimulation [TMS]). PET and fMRI are three dimensional imaging techniques that allow reconstruction of data according to tomographic slices.63
PET measures regional cerebral blood flow as a marker of
Interhemispheric asymmetry and clinical outcome
In studies of patients with first ever, monohemispheric stroke in stable conditions, 63% of those with recordable somatosensory evoked fields in the affected hemisphere had excessive interhemispheric signal‐strength asymmetry, and nearly 80% of dipole pairs (from homologous regions in the two hemispheres) were asymmetrical with increased signal strength in the affected hemisphere compared with the unaffected hemisphere after a cortical lesion. Asymmetry has been defined in control individuals.23
Effect of rehabilitation procedures
Plastic changes after stroke can result from passive adaptation of the brain to the lesion, spontaneous recovery of (partially) damaged brain tissue, behavioural consequences of the lesion (eg, decreased use of a formerly paretic limb), or therapeutic intervention. Reorganisation in response to therapeutic intervention can be studied in patients in the chronic stage of stroke. At this stage, the probability of any spontaneous recovery is negligible and, therefore, any recovery is likely to be
Combined imaging techniques
Methods of functional brain imaging have been combined in a few studies. In a patient with aphasia and severe right paresis after stroke who showed excellent motor recovery over a period of 12 months, fMRI, TMS, and magneto‐encephalography all indicated an asymmetrical enlargement and posterior shift of the sensorimotor areas in the affected hemisphere.132 In patients with asymmetrical organisation of the affected hemisphere, there is a good correlation between fMRI during median‐nerve
Conclusions
The study of neuroplasticity has clearly shown the ability of the developing brain—and of the adult and ageing brain—to be shaped by environmental inputs both under normal conditions (ie, learning) and after a lesion.134 Neuronal aggregates adjacent, or distant, to a lesion in the sensorimotor area can progressively adopt the function of the lesioned area. Imaging studies indicate that recovery of motor function after stroke is associated with a progressive change of activation patterns in
Search strategy and selection criteria
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