Many of us look upon sleep as a huge, boring waste of time, but nothing could be further from the truth: your sleep time is when your brain is literally rebuilding itself and is critical for memory and neurotransmitter levels. I would argue that Sleep, Exercise and Diet: are your greatest and truest friends.
During the REM cycles of the night, the body replenishes badly needed stores of neurotransitters. Particularly important is the rebuilding of seratonin and norepinephrine, which are critical neurotransmitters used for learning and retention that are normally depleted during the day.  In fact, during REM sleep the cells that use seratonin and norepinephrine actually become inactive, allowing the brain to more effectively rebuild itself. Again, one secret to brain power is quality of sleep.
Evidence is continuing to mount that lack of sleep helps lead to dementia. Of course, this is no shock because anything that leads to increased arteriosclerosis, inflammation and high blood pressure is bound to lead to troubles for your grey matter as I discuss in this link on Sleep and Erectile Dysfunction. In addition, scientists recently found that poor sleep also directly increases beta amyloid and the associated plaques that are so characteristic of Alzheimer's.  You don't want plaque in your brain anymore than you want it in your arteries!
Lack of sleep also whacks testosterone and growth hormone and both of these are critical for proper male brain function and cognition. Studies have shown that both are about linear based on the amount of sleep. In other words, the more sleep, the more testosterone and growth hormone. You can read more in my pages on Sleep and Testosterone and Sleep and Growth Hormone.
Many sleep experts believe ten hours of sleep is optimal. The reason? Well, for one thing, they have found that cultures without all the insane busyness of modern life typically sleep ten hours. Of course, to most of us that would seem impossible. But it still pays to know their reasoning: studies have shown that at ten hours we run at optimum performance. In other words, if you have times in your day where you need sheer speed and responsiveness, then ten hours is what you need. In other words, lots of sleep is required for the brain to achieve its maxium speed and responsiveness. (CAUTION: Too much sleep has been shown to lead to weight gain, so be careful here.)
In fact, some would argue that you are so efficient with this much sleep that it more than makes up for the loss of time while you are sleeping. Here is a quote from Dr. Haas in his excellent book Power Sleep that perfectly describes this concept: "[Researchers] have demonstrated that alertness significantly increases when eight-hour sleepers who claim to be well rested get an additional two hours of sleep. Energy, vigilance, and the ability to effectively process information are all enhanced, as are critical thinking skills and creativity". 
If you are looking for sheer mental and physical horsepower, sleep needs to be your engine.
16) Power Sleep, Dr. James B. Mass, 2001, p. 54.
17) Power Sleep, Dr. James B. Mass, 2001, p. 41
27) Science, Science Express Index, DOI: 10.1126/science.1180962, Published Online September 24, 2009, Submitted on August 24, 2009, Accepted on September 11, 2009, "Amyloid- Dynamics Are Regulated by Orexin and the Sleep-Wake Cycle", Jae-Eun Kang, et. al