Brain circuit for scratching. We have cells 1: Output cell it fires action potentials to cause scratching , Cell 2: excitatory neurons outside circuit presynaptic cell at excitatory synapse with cell 1 ,and Cell 3: neurons outside of circuit is excited when someone isnt scratching for presynaptic cell for inhibitory synapse at cell 1 . If itchy human tries not to scratch but does start scratching the circuit is doing what? A person who is itchy decides not to scratch what happens to the circuit?.