I was thinking yesterday about the difference between the way things are computed/processed in digital electronics and the way they work in the brain. What are the differences? What are the advantages of each? How would a computer work with neural networks and how would a brain work with digital circuits?

Digital Logic:

In a computer, everything is built out of transistors. All signals are discrete, either on or off, 0 or 1. Latches and flops are built out of transistors, and nand, nor, and not gates are built out of transistors. From these come all the processing in a computer. Each of these gates takes some number of inputs, which are all defined as either 0 or 1. Then depending on the type of gate, it has some defined rules, and there will be an output of either 0 or 1. Everything in digital logic is deterministic: if you know what the inputs are, you can always tell what the output will be.

Neural networks:

In a neural network, everything is arranged from neurons rather than transistors. The neurons connect to each other through synapses. One neuron can have many others connected to it. Each of these neurons may fire and send a signal through their synapses to the next neuron. If one neuron has enough neurons sending signals to it then it will eventually reach a point where it will fire and send a signal through its synapses. It could fire if one neuron sends a particularly strong signal to it, or if many neurons together send small signals that add up to a significant one. Basically it sums the incoming signals over time and space and if they cross some threshold, this neuron will be activated. The thresholds change and adapt depending on how often each synapse fires. As the firings decrease, the neuron becomes more sensitive to it, and as it fires more the neuron becomes less sensitive to that synapse. Neurons can also grow new connections to other neurons. The neural network is non-deterministic, the same inputs may not always result in the same outputs because the thresholds at different synapses may have changed or completely new neuronal connections may have been created.

Differences/Benefits:

One main difference is that neural networks can adapt and change. Another difference is that neural networks have more values than just on and off. A neuron could be not firing at all, it could be firing a little, it could be firing a lot, or somewhere in between. A neuron could fire so often that other neurons become insensitive to its input. Instead of a simple OR gate in digital logic, where the gate turns on when either input is on, neurons would be less discrete. The neuron may turn on some if either input firing a lot, or if both are firing some, and the neuron may fire a lot if both inputs are firing a lot.

How could a computer be designed using neural networks?

Well, to start, it wouldnt be too hard to design a chip that could act like a neuron, summing inputs over time and measuring them against some changing threshold. I’m not sure how new neural connections would work since these connections would seemingly be hard wired. But all the logic used for computer processing would have to be changed since it is all set up for digital design. Instead of AND/OR gates you might have neurons that require a strong input to activate and neurons that require a small input to activate. And how their adaptations would affect the computing, I have no idea.

How would a brain work with digital circuitry?

Any “brain” that uses digital circuits could not really be considered a brain. There would be no adaptation or change in the brain and so it doesn’t seem much like a brain to me.

This brings up another good question: what is it that gives us our humanity? our consienceness and intelligence? Is it the fact that the brain adapts and changes and develops? Or is it something inherent in the circuitry of the brain? What separates our brains from monkeys? What separates our brains from computers? What makes us who we are?