The first artificial neuron

In 1943, two researchers asked a simple question: what is the minimum a neuron needs to do?

Their answer: receive signals, add them up, and fire if the total is high enough.

To keep things simple, they made every signal binary — either on or off, nothing in between. Click the input neurons on the left to toggle them.

Every circle is a neuron. The three on the left send signals. The one in the middle receives them and decides whether to fire. The threshold is 2 — one signal isn't enough, two crosses the line.

When the middle neuron fires, it sends its signal onward. That output could feed into more neurons further down the chain.

Neurons don't only receive signals from the outside world (the way your eyes send signals to your brain when you see something, or the way a camera feeds images into a machine). They also receive signals from each other. One neuron fires, and that triggers the next.

That's the key idea. The threshold of 2 here is just an example — we'll get to where numbers like that actually come from in a few slides.