Figure 2.

Conditioned place avoidance (CPA) and conditioned place preference (CPP) assays reveal the affective component of pain in octopus

In trials where initially preferred chambers were paired with 0.5% acetic acid (AA) injection, octopuses spent less time in their initially preferred chamber in a post-training period of free exploration, compared with octopuses receiving saline. In trials where octopuses received lidocaine over an area of prior injection (either saline or AA), octopuses preferred the chamber paired with lidocaine only if they had previously been given AA injection. Points show individual change in time values for each subject. Different animals were used to test each condition. Central, wide bars show the mean and whiskers show standard error of the mean. Asterisks indicate significant between-group differences (Bonferroni post-hoc test, ∗∗p < 0.01).