Gating can occur by shunting inhibition in which inhibitory interneurons change the membrane conductance of an excitatory target axon, thereby diffusing its excitatory signal. A gating signal from the gatekeeper triggers these inhibitory interneurons in order to prevent one set of neurons from firing even when stimulated by another set. In this state, the gate is closed. Examples of this kind of gating have been found in visual cortical neurons and areas of the prefrontal cortex (PFC) in primates that may be responsible for suppressing irrelevant stimuli. Studies suggest that this kind of inhibition can be attributed in part to GABA receptor-mediated synapses.