There is some currently promising research being done on brain plasticity.  Below is a recently published study.

http://medicalxpress.com/news/2013-09-cognitive-brain-function-cancer-survivors.html

This is not the only perspective available. The practice of mindfulness meditation as well as the effects of depth psychotherapy have all shown that the mind has a capacity for growth and change.  I explain this to myself and my clients in a simple way: it’s like the brain has grooves that represent the well-worn patterns of thought and beliefs that we carry inside of us, with enough experiences that are different we can actually shift these grooves  into different patterns.  In essence, there is hope that we do not need to be trapped inside a fuzzy mind!