Extrasynaptic receptors are essential for producing activity in this striatal neuron. Neurons were recorded from brain tissue slices in three different conditions. In graph 1, the researchers electrically stimulated a neuron without any extrasynaptic response, or in a "down" state. In graph 2, the researchers added the neurotransmitter NMDA. This lifted the membrane potential, and made it possible to provoke many action potentials with electric stimulation. In graph 3, the researchers added memantine and showed that the drug blocks nearly all action potentials by blocking most extrasynaptic activity.