How fast does the human brain compute, and how much information can it store?
There are several ways to answer the question about how fast the brain processes information.
The best answer for this question can be obtained because we have good estimates for the three main variables that enter into it: how many neurons (brain cells) we have, how fast a neuron can fire, and how many cells it connects to. A human being has about 100 billion brain cells. Although different neurons fire at different speeds, as a rough estimate it is reasonable to estimate that a neuron can fire about once every 5 milliseconds, or about 200 times a second. The number of cells each neuron is connected to also varies, but as a rough estimate it is reasonable to say that each neuron connects to 1000 other neurons- so every time a neuron fires, about 1000 other neurons get information about that firing. If we multiply all this out we get 100 billion neurons X 200 firings per second X 1000 connections per firing = 20 million billion calculations per second.
This estimate might easily be off by an order of magnitude- that is, it might be 10 times too high or low. It also is a bit misleading because it estimates the raw 'clock speed' of the brain, which is much higher than the number of real useful calculations we do in a second. An apparently much simpler way to approach the problem is to note that the time it takes for the brain to make a really simple decision- like naming a picture or reading a word aloud- is about 300-700 milliseconds. So we can say that brain can only make about two conscious calculations per second. However, this is also misleading, for a bunch of reasons. One reason is that many well-trained brains can make incredibly complex decisions that quickly. Moreover, even simple tasks like reading a word aloud are actually very complex, actually requiring huge amounts of low-level computation. Finally, note that your brain is doing all sorts of things unconsciously at the same time- maintaining your body and its relation to the world- whenever you are engaged in conscious calculations. So depending on whether you want the raw clock speed, or some higher-level measure of information processing, your question has two answers that differ widely.
It is interesting to put this into the perspective of contemporary technology. The 'clock speed' of a neuron is abysmal by technological standards. The central processing unit in the machine on which I wrote this document has a 1 Ghz. clock speed, which means it runs1000 million clock cycles per second. If we divide 1000 million by 200, we see that the CPU on my computer is 5 million times faster than the clock speed of a neuron. Of course the computational power of our brains comes from the fact that we have a lot of neurons. Nevertheless, the gap between technology and neurons is closing fast. It has been estimated many times by many different people, using uncontroversial projections into the future (the exponential growth curve suggested by Moore's law), that we will have a computer that can process as many bits per second as the human brain within a few decades at most. Soon thereafter, computers will exceed human beings in raw processing power. If you are under 50 years old as you read this, then you can reasonably bet that you will own a cheap desktop computer that will process more information than your brain does before you die (Ray Kurzweil estimates that cheap computers will process this fast by 2023). If you are under 25 years old, there is a good chance that you will own a cheap desktop computer that processes more information than the whole human race (Ray Kurzweil estimates that cheap computers will process this fast by 2049). This does not necessarily mean that the computers will be as intelligent as you or as a small town full of people, since at the moment we have no idea how to program computers to be generally intelligent.
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