Compensatory contribution of the contralateral pyramidal tract after experimental cerebral ischemia

Many people escape sudden death from ischemic brain stroke, but suffer from severe disabilities such as aphasia and/or paralysis. These survivors of focal brain injury need chronic care to recover from and/or compensate for the impaired sensory and motor functions previously controlled by the focal ischemic core. Functional compensation not only involves the remaining brain areas around the infarction but also the areas contralateral to the stroke lesion, with the need for remodeling of neuronal circuits in some cases. In this review, recent human and animal studies are presented to aid in the understanding of such plasticity in areas contralateral to the stroke lesion providing a new model for rehabilitation. It is well known in the medical field that the intact contralateral hemisphere is recruited for functional remodeling of modalities such as speech. However, the detailed mechanisms underlying these phenomena are less clear. In rodents, in vivo imaging techniques combined with other traditional techniques such as electrophysiology and behavior have revealed that functional recovery is achieved by specific synaptic (neuronal circuit) remodeling of the contralateral area in the 1st week after a focal stroke. The intact contralateral hemisphere can therefore potentially adopt a bilateral function, even in adults, following proper remodeling of neuronal circuits. These recent results suggest a possible new pathway using the intact hemisphere's function to recover lost functions stroke patients.