Timid does not like the light. With one rod photoreceptor, it senses light and drives the wheels forward when it senses light. When the photoreceptor leaves the light, the NeuroBuggy stops.
Paranoid has 1 rod photoreceptor that it uses to navigate its environment. It uses two interneurons and two motor neurons to do so, but the two sides of the circuit are connected a bit differently. The "light" output on the rod drives both wheels forward, while the dark output drives just the left wheel backward. This results in a NeuroBuggy that follows the edge of a light halo.
Stubborn has paired two neuron oscillators on it. When the front touch sensory neuron is activated, the touch inhibits the "forward" oscillator and activates the "backwards" oscillator. When the rear touch sensory neuron is activated, the opposite happens. This circuit causes the NeuroBuggy to run back and forth between two objects.
The Indecisive NeuroBuggy can't make up its mind. When it's in the light, it will drive forward until it reaches a shadow. When it reaches a shadow, it will reverse and drive back into the light.
Driven is a phototropic vehicle, meaning that it moves towards the light. The connections between Interneurons and Motor Neurons are crossed from right to left, so light shone into the left Rod Photoreceptor will cause the right Motor Neuron to drive the right wheel forward, and vice versa.