M5 Post-injury neuroplasticity (cortical reorganization)

Topic

Following a brain injury, remaining brain tissue can undergo functional reorganization through plasticity mechanisms that directly utilize the same cortical network effective connectivity and synaptic weight plasticity previously described in other models.

Rehabilitation promotes the recruitment of cortical areas adjacent to the injured zone by the remaining brain tissue; the closer a cortical area is to the injury site and the more intensive the rehabilitation training, the more that adjacent area is recruited to take over the lost function. Furthermore, rehabilitation can transiently reopen a plasticity window within the remaining brain tissue—similar to the critical plasticity window described for nervous system development—which explains why early rehabilitation is generally more effective than late rehabilitation.

Functional recovery of the remaining brain tissue follows an exponential learning curve: improvement is rapid at the start of rehabilitation and subsequently slows down until a stable level of residual function is reached. During this process, different cortical representations within the remaining brain tissue compete for available territory; in this dynamic, the representation that activates most strongly or frequently tends to claim the majority of the available space, at the expense of other representations competing for the same area.

In cases of extensive injury to the remaining brain tissue, some lost function may shift to the contralateral hemisphere—a process known as homotopic reorganization. Additionally, rehabilitation intensity has a direct dose-response effect on the speed of recovery in the remaining brain tissue: the more intensive the rehabilitation, the faster the recovery. Ultimately, it is this very remaining brain tissue—recruiting adjacent cortical areas, transiently reopening its window of plasticity, competing for territory among its cortical representations, and, in extensive cases, transferring function to the contralateral hemisphere—that determines the extent and rate of functional recovery following a brain injury.

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