Past experiments by Kruk and other researchers have demonstrated the ability of cephalopods to produce a reflexive response to stimuli by learning not to make contact with them. The fresh experiment went further. After training in a 3-chamber box, clams that had been injected with acetic acid in their tentacle no longer swam into the chamber in which it happened. And those injected with normal saline did not produce a similar reaction.
Next, the cephalopods who received the painful injection were injected with an anaesthetic, and they subsequently preferred to stay in the chamber in which they felt rapid pain relief. Those who received a saline injection showed no interest in the “painkiller” chamber.
In addition, as Crook found out, cephalopod mollusks are capable of distinguishing different types of pain in different places of their own body. The specialist recorded a prolonged peripheral response on the way to the clam’s brain, in all likelihood reflecting the intensity of pain from acetic acid injections.
