Specifically, normal people who suffer brain injuries may develop increased mental abilities.
How could damage to the brain increase brain function?
Because damage to portions of the brain which inhibit our brain-processing power allow us to become aware of such faculties.
Scientists at the University of Australia who have studied this issue conclude that we all probably have the ability to activate heightened brain functions without comprising normal brain functions (and we don't need to get hit in the head to do it):
So, if all of us have latent super-abilities, is it possible to activate them permanently, or at least periodically, without compromising normal brain functioning? Probably, say the Australian scientists who used transcranial magnetic stimulation to temporarily switch off the frontal temporal lobe of volunteers. Afterwards the subjects showed an immediate improvement in calendar calculating, naming the day of the week of any recent history event, and in their artistic abilities. Of course these were just the abilities tested. Scientists do not know all of the latent abilities that humans may possess.