The Neuron was inspired by a paper on neural computing and is a variation of a typical analogue neuron circuit. It can be used as a complex audio waveshaper, gate or pulse generator, CV shaper or to generally mess things up. The diff-rect is a hybrid of two basic op amp ‘building blocks’ – a difference circuit and a rectifier. Not sure if I have ever seen the two merged together before. It is probably a bad idea except for synth use, where it is a wonderful idea!
The Difference Rectifier has 4 inputs (two + & two -) and two outputs. The Neuron has 3 inputs and one output, the pots control when the neuron will react to incoming signals and how much it will react.