I'm a big believer in neuroplasticity. That just means the brain getting better with practice. As scientists are better able to map the brain's acitivity levels, there's more physical evidence emerging to demonstrate that the brain adapts according to the demands placed on it. It used to be common thinking that only the developing brain could be adaptable. In neuro-psych terms, "developing" refers to up to the age of twelve, not eighteen or twenty-one or whatever age is considedred "adult".
After that age, we're losing more neurons than replacing them. This view makes the adult brain sound set in its ways and very reluctant to incorporate new information and skills. Teach an old dogs new tricks? Hmm, unlikely!
But the good news is that even if we aren't scoring any new ones, they can still form new connections. And those connections become stronger every time we practice them. Some areas of the brain can be taught to take on tasks that typically weren't part of its job description (the brain is a structured organ, with particular areas being responsible for very specific skills, such as Broca's and Wernicke's areas being the parts of the brain responsible for understanding and producing language).
What's my point? What's that got to do with procrastination? Heaps, actually. Procrastination is a bad thinking habit. If I believe that I have more important things to do than to write, such as watch television, I am training my brain to become a passive absorber of ridiculous information presented to be on the screen. But if I force myself to write (to write anything) then I'm getting into the habit of exercizing my brain to generate sentences, paragraphs, and pages of narrative. I'm making it choose words. I'm forcing it to sound out sentences to judge how well they flow. I'm asking it to make decisions about my characters and situations. I'm projecting the situations into the future and planning what sorts of actions my characters will take to solve their problems. In short, I'm practicing the very skills that I really want to become efficient at doing. Sure, often I produce crap. And, yes, it's tiring and I sometimes wake up feeling hung-over. But it's all good.
Everytime I make the choice to write rather than to do something else, I'm shaping my brain to become the brain I want.