You might want to consider carefully how much time you spend awake and thinking. Recent research has shown that the aggregate number of connections in your brain increases during wakeful states and, as is well known from previous decades' brain research, losing connections during childhood is a major part of developing a mature, intelligent mind.
Super geniuses Stephanie Maret, Ugo Faraguna, Aaron B. Nelson, Chiara Cirelli, and Giulio Tononi of the University of Wisconsin have been monitoring the brain growth of groups of mice in order to learn more about neuronal dynamics. What they've discovered and the work it's built on may come as quite a surprise.
Using mice that were genetically engineered to express a yellow fluorescent protein in their brains and two photon microscopy, the researchers took a look at isolated dendritic branches in their motor cortices. They photographed the section of dendrites in a mouse, then subjected it to a regimen of normal sleep, reversed sleep (diurnal rather than nocturnal), or sleep deprivation. Then they photographed exactly the same group of dendrites again to get a comparison of the spines. These science fiction techniques revealed a tiny world teeming with activity.
The dendritic spines, the tiny projections between a target neuron and an input from a neighboring neuron, moved about with vigorous life and with all sorts of different kinds and activity levels. Lots of connections were being made and lost, mostly in the smaller dendrites. As many as about 10% of the connections within view in the researchers' pictures were made new or disconnected in the span of about 15 hours during which all this research took place. The rule seemed to be that the smaller the dendrite, the less stable the connection. Filopodia, the tiny dendrite buds that can mature into full connections, were bubbling away on the surfaces of the neurons; though they constituted only about 1 in 40 dendrites they accounted for nearly a quarter of all changes observed. On the other hand, large and mature mushroom dendrites didn't change at all in this study.
What was most important though, and the thing the researchers most wanted to know, is what role sleep played in building and losing dendrites. They hypothesized that the mice would have a net gain in dendrites during wakeful states and a net loss during sleep. Using three groups of mice they determined that their hypothesis was correct. They found that forcing the mice to stay awake during the day when they prefer to sleep and having them sleep at night instead had no effect so long as the total amount of time they slept was the same as the mice who got to sleep on their natural schedule. Even more interesting, they found that sleep deprivation would cause the number of dendrites to keep climbing and climbing until the mice reached such a state of exhaustion that they were really in a state of half-wakefulness, at which point the number would stop increasing.
This research could help to explain something about mental exhaustion and why those late night study breaks don't really help so much. Apparently the brain has a limit to the number of mental acrobatics it can do in any given wakefulness cycle before it needs to shut back down and recharge, the meaning of the recharging partially being that it's removing a massive number of dendrites. Then again, it helps to elucidate the lives of children and babies with their long sleep cycles which are apparently necessary to accommodate all the extra dendrite loss they experience.
This research is only the first in what could be a wide world of new discoveries of the differences between the waking and sleeping brain. For a closer look into this study and to review its excellent and exciting references, find it in the November, 2011 issue of Nature Neuroscience under the title "Sleep and waking modulate spine turnover in the adolescent mouse cortex".