The prefrontal cortex sits curled up behind your forehead, and monitors your actions like an overprotective mother. Don't run with scissors. Don't eat the whole box of thin mints. Don't jump off the roof into a dumpster.
It busies itself with impulse control, making sure we don't do every crazy thing that pops into our heads. Unlike most other animals which survive on reflex, our brains have evolved to plan ahead, allowing us to change our behavior based on the calculated consequences of our actions. These calculations occur in the prefrontal cortex, which evaluates potential behaviors, and vetoes the ones with negative outcomes. Interestingly, the prefrontal cortex doesn't so much ensure that we do the right thing, but rather makes sure we don't do the wrong thing (n.b. make note of the distinction as it can lead to problems in itself). In short the prefrontal cortex has evolved to say "No."
The prefrontal cortex is the newest development in the evolution of the brain (if you believe in stuff like evolution). It's very fashionable these days, all your favorite mammals have one. An advanced subdivision of the neocortex, which is itself the most advanced processor of the brain, it is most highly developed in dolphins, monkeys, chimps, and humans. Lizards, geckos, dinosaurs, eagles only have/had a brain stem and other structures that lie buried deep in our own brain. The reason these reptilian structures lie buried inside us is because once mammals came along, we laid down more processing power on top of the archaic hardware. The newer processing power comes from the neocortex, which covers the surface of the brain, and causes our brains to wrinkle and fold like the backside of a newborn Benjamin Button.
As humans evolved from lower animals (I apologize for the blatant speciesism), the front part of the neocortex (frontal cortex) began to blossom. Once evolution reached monkeys and chimps, the leading edge of the frontal cortex (the prefrontal cortex) mushroomed even more to become the monstrosity it is today. In fact the prefrontal cortex may be too big for our own good, sometimes causing unnecessary anxiety and getting in the way of our happiness.
The prefrontal cortex makes us each unique. Emotion, belief, motivation and behaviors are all influenced by activity in the prefrontal cortex. As a neuroscientist I've studied how the roots of depression can largely be attributed to erroneous prefrontal processing. It can pay particular attention to all the bad things in life and ignore the good, making people feel sad and helpless. As a coach I've informally, but more practically, examined the effects of belief, practiced behaviors, and motivation on athletic performance. The prefrontal cortex might be the reason Kobe misses an important free throw, even though he's practiced it thousands of times (ok, bad example, Kobe would never miss a clutch free throw).
As I try to procrastinate from finishing my dissertation, I'll use this blog to explore the interesting facts and theories I've learned in neuroscience and how they apply to living a life full of happiness and free of anxiety. I haven't mastered this myself, but I have learned something about the neural processes that contribute to it. If you have any specific questions about neuroscience, the brain, or behavior, please leave a comment. Whatever part of the brain you're interested in, I'll be happy to expose it.