Brian 
viju 
ClockLink 
Kai 
DreamersI.com 
partha.mukherjee 
Kenichi Uchikura 
quecrookie 
brett 
MES, Inc. 
You may sometimes hate your job, but if it's intellectual taxing or involves a lot of multitasking, organizing, and managerial skills, then you should be thankful for it.
A study conducted by psychiatrists at Duke University showed that mentally demanding jobs keep the brain healthy. Healthy brain keeps one way from dementia as well as Alzheimer's disease. The research studied found that the jobs that were most beneficial to these folks included the higher degree professions such as law, medicine, journalism and other careers that required multitasking, organizing and managerial skills.
But I say it's not only careers that can make our brain active. Not contrary to the research, but based on personal experience. These are people who took their hobbies as their job, meaning you get paid for it. One example is photographers, film-makers, writers, and many others that which doesn't belong to the degree proper. These Artists are equally keeping positive mind-setting to hone their craft. Always on-the-go!
It only means that, if your mind works positively all the time it surely is an active brain.