Table 1.

Criteria for pain perception [10,98].

Criteria	Species
(1) Nociceptors	M, B, A, F, C, D, I
(2) Pathways to central nervous system	M, B, A, F, C, D, I
(3) Central processing in brain	M, B, A, F, C, D, I
(4) Receptors for analgesic drugs	M, B, A, F, C, D
(5) Physiological responses	M, B, A, F, C, D
(6) Movement away from noxious stimuli	M, B, A, F, C, D, I
(7) Behavioral changes from norm	M, B, A, F, C, D, I
(8) Protective behavior	M, B, A, F, C, D
(9) Responses reduced by analgesic drugs	M, B, A, F, C, D, I
(10) Self-administration of analgesia	M, B, F
(11) Responses with high priority over other stimuli	M, F, C, D
(12) Pay cost to access analgesia	M, B, I
(13) Altered behavioral choices/preferences	M, B, A, F, C, D, I
(14) Relief learning	M, B, I
(15) Rubbing, limping or guarding	M, B, F, C, D
(16) Paying cost to avoid stimuli	M, B, F, D
(17) Trade-offs with other requirements	M, B, F, D

M = Mammals, B = Birds, A = Amphibians/reptiles, F = Fish, C = Cephalopods, D = Decapods, I = Insects.