The top-half is a "Neuron" circuit. This is a three-input mixer that runs into a half-wave rectifier and comparator. The comparator's bipolar output is summed with the rectified signal. SENSE adds a positive DC signal to the mix, while RESPONSE affects the magnitude of the comparator's output. The values of the knobs here are accurate to the original hardware, and are not bipolar like my first Euro Reakt port.
The Diff-Rect (Difference Rectifier) is another creative mixer. The two "+" inputs are summed together, and the two "-" inputs are summed together. The "-" mix is then subtracted from the "+" mix. If the result is positive, it goes out the "+" output, otherwise it goes out the "-" output.
If this seems complicated, just experiment!