Figure 3.

Precise and specific wound-directed grooming behaviors show discriminative pain experience in octopus

Top panel shows examples of wound-directed behaviors, and colors surrounding each image correspond to shaded frequencies in stacked bars, below. Arrowheads indicate the location of AA injection on the arm. Behaviors were observed during training trials and 24 h later. AA-injected octopuses showed sustained wound attention and concealment that persisted for at least 24 hr after AA injection. Skin removal behavior was observed in all AA-injected animals, suggesting a specific representation of acid-induced pain that elicits a highly specific behavioral response. Bar acronyms: AA, acetic acid injection; S, saline injection; L, lidocaine injection after earlier AA injection; LC, lidocaine control (lidocaine injected after earlier saline injection). Numbers inside bars in first panel (5 min) are group sample sizes, which are the same for each subsequent interval. Asterisks indicate significant difference in proportions of animals performing each behavior, relative to saline-injected controls (fishers exact tests, ∗p < 0.05, ∗∗p < 0.01, ∗∗∗p < 0.001.