I thought I'd share this article with you because it explains very well why people with Parkinson's behave the way we do. The lack of motivation, mood swings, binge eating, gambling, risk taking behaviour, constant craving for something to lift your mood, pleasure seeking activities.
Some interesting questions are raised ~ read on, I think you'll find it interesting?...
"...It is the role that dopamine plays in pleasure and motivation that attracts the most neurobiologists attention as well as mine.
In certain areas of the brain when dopamine is released it gives one the feeling of pleasure or satisfaction. These feelings of satisfaction become desired, and the person will grow a desire for the satisfaction. To satisfy that desire the person will repeat behaviours that cause the release of dopamine. For example food and sex release dopamine. That is why people want food even though their body does not need it and why people sometimes need sex. These two behaviours scientifically make sense since the body needs food to survive, and humans need to have sex to allow the race to survive. However, other, less natural behaviours have the same effect on one's dopamine levels, and at times can even be more powerful. Often these behaviours can result in addiction due their effect on dopamine, and that addiction can have negative effects on a person's well-being."
You can read the full article at: http://serendip.brynmawr.edu/bb/neuro/neuro05/web1/isiddiqui.html