"Octopuses make it notoriously difficult to get recordings from electrodes inserted into the brain, because they can selectively shut off blood supply to an area of their body or brain. That's if they allow the researchers to insert electrodes at all. Jennifer Basil, a cephalopod researcher at the City University of New York tells the story of one colleague who took on that challenge: "He thought the octopus was anaesthetised, so they put the electrode in and the octopus reached up with an arm and pulled it out." That marked the end of his work with octopuses. "He has worked with lots of animals but he said 'that animal knows what I'm thinking. He doesn't want me to do this so I'm not going to'," Basil says."
Eight arms, big brain: What makes cephalopods clever, Caroline Williams, New Scientist 2816, 2011