A bowl of popcorn??? So here is how I think of it. You have a bowl of popcorn and you want to see a double feature. You want to eat all the popcorn but it is important to eat it sparingly during the first movie so you have some left over for the second.
After brain injury (stroke, trauma, infection, surgery), the brain displays an impressive ability for neuroplasticity. There are increased proteins and special signalling molecules that create an environment ripe for new connections to be made between neurons. This is called “injury-induced plasticity”. Some researchers suggest that the conditions within the brain after injury resemble the brain during the early developmental stages. (Most of this research has been done in rodents that are given an experimental ‘stroke’ but research results likely apply to humans and to brain injury conditions other than stroke).
So this heightened period of sensitivity after injury is an opportunity to sculpt neural circuits. This is essentially the “neuroplasticity window” (if you forgot about the neuroplasticity window, read The brain opens a neuroplasticity window under Neuroplasticity Basics). But the window is open for a select period of time and there is only so much capacity. This is the bowl of popcorn (which will make sense shortly I promise). The experiences of the brain-injured person within weeks after the event will influence how the neural circuits are sculpted (read What is Neuroplasticity? and Neuroplasticity is all about chemicals and synapses to refresh your memory). This is why after brain injury, it is important the survivor has the right type and intensity of therapy to help recover physical abilities, thinking, emotion and language.
Let’s go back to the bowl of popcorn. Imagine that after a stroke or brain injury, a right-handed person has weakness of their right hand. Well-meaning health care staff and family encourage that person to use their unaffected left hand to eat, to wash and to move about in bed. Within a week or two, the formerly right-handed person and their family are quite pleased with his level of independence using his left hand. He can now button up his shirt and tie his laces with one hand! The capacity of the brain is remarkable and it has only been 3 weeks! Remember that the neuroplasticity window is limited by both time and capacity. Our brain injury survivor has just used up about 1/3 of his ‘open-window’ time and about ½ of his neuroplastic capacity to improve the control of his unaffected hand (not his affected hand). So in terms of the bowl of popcorn, he has very little left for the second show-the synaptic connections that need to be made to promote recovery.