98 billion neurons are plenty

This is your brain after a stroke.

There are over 100 billion nerve cells in the human brain. A typical stroke kills only 2 billion of them.

That's where neuroplasticity comes in. Neuroplasticity is the ability of our brain neurons to take on -- or change -- their functions. Neuroplasticity occurs during normal brain development when the immature brain first begins to form. But it also occurs all the time (think, learning) and plays a major part after a stroke, as the brain tries to compensate for lost function or to maximize remaining functions.

We use 100% of our brains, but which the neurons are used for which functions can change. This is why stoke survivors can get back functionality, like walking. The brain can simply re-route and re-use old neurons to new uses.

Some books about neuroplasticity:


Four principles of neuroplasticity
  1. Use it or lose it: It has been shown that movement of the affected limb in hemiparetic stroke patients improved when they were forced to use the limb and overcome“learned nonuse.” This method, constraint-induced movement therapy (CIMT) is centered on massed practice and with the forced use of the affected limb. These principles have been applied to aphasia treatment as well in what is called constraint-induced language therapy (CILT) with encouraging results.
  2. You’re never too old: The injured brain, regardless of age, is flexible and capable of change throughout its lifespan. This means you can improve both -- sometimes significantly -- many years following your stroke. 
  3. Repetition matters: Repetition is important in maintaining changes in the brain and their corresponding functional benefits. This supports the need for long-term, consistent use of a skill to produce lasting changes. 
  4. Intensity matters: The more intense the treatment, the greater the skill acquisition and change. Therapy provided at a higher frequency for a shorter period of time gets better results.
A simple animation about neuroplasticity:

For a more in-depth discussion, you can view this Ted talk by neuroscientist Michael Merzenich: