I recently came across an article in Scientific American which explores the potential and limitations of the human brain as it relates to physics. Many people, including myself, wouldn’t mind doing something that could improve our brain’s capacity for intelligence, but is this a realistic goal? Some scientists argue that the brain is so close to its physical limits of neural communication that evolving or developing a more intelligent, faster working brain is physically impossible. Understanding why this might be the case has been ongoing for a couple of centuries.

                When it comes to brains, size does and does not matter. A cow has a larger brain than a mouse, but a cow is not any smarter than a mouse. Elephants have larger brains than humans, but we are vastly more intelligent creatures. Some theories propose that bigger animals need larger brains because there is more “housekeeping” to do within the body. This certainly makes sense, but it also demonstrates that more neurons does not necessarily mean a higher intelligence, but it does mean more energy and oxygen consumption within the organism. So how could humans become smarter?

If humans brain size increased dramatically, the toll on our metabolism would simply be too great. The human brain already comprises 2% of our body mass (on average) and consumes over 20% of the calories we burn every day. In addition to oxygen consumption, more neurons and a larger brain would also mean more connections, longer pathways, and larger neurons but to make effective use of a larger brain, increasing the speed of transmission between neurons would also have to take place, and therein lies the problem.

                Many physicists agree that myelinated neurons are operating almost as quickly as possible. Perhaps slight increases in transmission speed are possible, but would that really do anything? If you double the width of the axon, you get about a 40% increase in transmission speed, yet you double the amount of energy it takes to operate that neuron. Thus increasing size and speed of actions potentials is ultimately unsustainable. Additionally, as brains get bigger, most of the size difference is devoted to wiring between neurons rather than increasing the size or number of the parts of the neuron that do the actual computing. So if increasing speed of transmission is unsustainable, and increasing size is counter-productive, how can humans become smarter?

Some researchers attribute differences in intelligence simply to more efficient and effective neuronal connections. Is it possible to shape and mold these connections artificially? Rather than increasing speed of transmission or size of the brain, perhaps researchers should focus on organization and creating stronger and more effective pathways in the brain. Perhaps decreasing the size and density of neurons in the brain could create the potential for more neuronal connections? Researchers have determined that this is what separates our brain from say a rats. Would decreasing size, density, and effectiveness of communication lead to a “smarter” brain? Some certainly think so.

http://www.scientificamerican.com/article.cfm?id=the-limits-of-intelligence