Fear not, Binkie...
The "tiny empty cavities" in your brain are really a good deal larger than you may think.
The brain has a very large capacity for information storage.
It was once thought that brain cells (i.e., nerve cells) could not be regenerated if they were destroyed. I believe this has come into question.
There is one thing that I am aware of—even if we cannot INCREASE the number of brain cells that we have, we can definitely INCREASE the number of interconnections BETWEEN the brain cells.
So, all is NOT lost.