To give you a little additional detail:
Most Inputs are only ever positive. The exceptions are the Sensory Angle Inputs for Vision and Scent, which give the angle from the Critter to the strongest Scent or "most significant" (as a function of size, proximity, and taking camouflage into account) nearby visual object. The Angle inputs are positive or negative according to which side of the Critter the sensation comes from.
Similarly, some outputs only really do something if they're Active with a positive value, but there are also exceptions. Left and Right rotation do nothing if negative, but the Forward/Back output neuron causes the Critter to swim forward if positive, backward if negative. The "Breed" output acts the same as long as it's active, regardless of positive or negative -- if the Critter has the energy, it will reproduce with a nearby compatible partner. If there's no nearby partner, it will check its energy levels again and reproduce asexually if it has the energy (Partnered breeding is half as expensive.) Finally the "Adrenaline" output works like this -- if the Critter is not "exhausted" (on cooldown) it will either puff its body up and go into a "Rage", temporarily boosting Strength, or stretch out its tail and "Sprint," boosting its Speed.