 In some instances of pain perception, mental imagery plays an even more central role: for example, phantom limb pain (pain some subjects feel in amputated limbs) consists of cortical pain processing (in S1/S2) that is not triggered by nociceptors (Ramachandran et al. 1995) for the simple reasons that the relevant nociceptors are missing (they have been cut off with the rest of the limb). Further, the thermal grill illusion (where applying warmth to the index and the ring finger and cold to the middle finger triggers strong pain sensation in the middle finger) is also an instance of sensory pain processing that is not triggered by nociception (Defrin et al. 2002). In both cases, as the nociception is missing, there is no pain perception, but only pain imagery.