This ability suggests two scenarios. The first is that we could scan portions of a brain to ascertain the architecture of interneuronal connections in different regions. The exact position of each nerve fiber is not as important as the overall pattern. Using this information, we could design simulated neural nets that will operate in a similar fashion. This process will be rather like peeling an onion as each layer of human intelligence is revealed. That is essentially the procedure Synaptics has followed. They copied the essential analog algorithm called center surround filtering also found in the first layers of mammalian neurons.

A more difficult, but still ultimately feasible, scenario would be to noninvasively scan someone's brain to map the locations, interconnections, and contents of the somas, axons, dendrites, presynaptic vesicles, and other neural components. The entire organization of the brain -- including the contents of its memory -- could then be re-created on a neural computer of sufficiently high capacity.

Today we can peer inside someone's brain with MRI scanners whose resolution increases with each new generation. However, a number of technical challenges in complete brain-mapping -- including achieving suitable resolution, bandwidth, lack of vibration, and safety -- remain. For a variety of reasons, it will be easier to scan the brain of someone recently deceased than a living brain. Yet noninvasively scanning a living brain will ultimately become feasible as the resolution and speed of MRI and other scanning technologies improve. Here too the driving force behind future rapid improvements is Moore's law, because building high-resolution three-dimensional images quickly from the raw data an MRI scanner produces requires massive computational ability.

Perhaps you think this discussion is veering off into the realm of science fiction. Yet, a hundred years ago, only a handful of writers attempting to predict the technological developments of this past century foresaw any of the major forces that have shaped our era: computers, Moore's law, radio, television, atomic energy, lasers, bioengineering, or most electronics -- to mention a few. The century to come will undoubtedly bring many technologies we would have similar difficulty envisioning, or even comprehending today. The important point here is, however, that the projection I am making now does not contemplate any revolutionary breakthrough; it is a modest extrapolation of current trends based on technologies and capabilities that we have today. We can't yet build a brain like HAL's, but we can describe right now how we could do it. It will take longer than the time needed to build a computer with the raw computing speed of the human brain, which I believe we will do by around 2020. By sometime in the first half of the next century, I predict, we will have mapped the neural circuitry of the brain.

Now the ability to download your mind to your personal computer will raise some interesting issues. I'll only mention a few. First, there's the philosophical issue. When people are scanned and then re -- created in a neural computer, who will the people in the machine be? The answer will depend on whom you ask. The "machine people" will strenuously claim to be the original persons; they lived certain lives, went through a scanner here, and woke up in the machine there. They'll say, "Hey, this technology really works. You should give it a try." On the other hand, the people who were scanned will claim that the people in the machine are impostors, different people who just appear to share their memories, histories, and personalities.