Brain Connections

The human brain has more than 100 billion neurons, with each neuron receiving input signals from 10 to 1,000 other neurons. Schematic representations of these connections in the brain always show an incredible web of lines representing the neurons, either as a 2-D or a 3-D image. Suppose you created a scaled down computer model of this human brain using only 1 million neurons in a 3-D space. On average, how many input connections would each neuron have? What is the surprise here?

Answer

A million neuron model of the brain is still quite a formidable programming task for a computer simulation, but there would be no information transfers from neuron to neuron. Why not? Because any neuron in this model of the human brain would have on average nearly zero inputs. One calculates as follows: if 1011 neurons have 1,000 connections each, say, then the average is 1 connection per 108 neurons. Therefore, a model with 106 neurons will not work as a useful scale model of the real brain.

Of course, one could simply take a small volume of the brain containing 1 million neurons and ignore connections to other parts. Or one could artificially modify the unusable computer model above by ensuring a few connections or more to each neuron. Whether the behavior that ensues is realistic must be determined. The more practical approach is to model a small section of the brain perhaps tens of thousands of neurons and all their interconnections in a focused study and simulation. A grid of computers, each representing one small section, could then be used to simulate a larger portion of the brain. Hopefully, when quantum computers become a reality, they will be able to simulate the whole brain. Whether the brain behaves quantum mechanically and requires quantum superposition for its operations is presently unknown.

There is the remarkable problem of information storage in the brain that is, where exactly is information stored? If each neuron stores only one bit of information, then the human brain is not large enough by many factors of ten! In 1989 Roger Penrose suggested that each neuron must be capable of storing many bits of information, in contrast to the prevailing ideas. Subsequently, the numerous microtubules in each neuron were found to participate in the information storage game. There still remains the question of what each stored bit of information represents.