The understanding part is not easy. These octopuses (mostly Pacific Giant species), scary as they can be, have followed such an entirely different evolutionary path that our assumptions can’t possibly fit, and yet interacting directly with them feels personal, both in their impact on the human and in the projection of individuality from each of them. They’re quite distinct from each other.
An octopus has no brain like ours, though their “head” has “eyes” quite a bit like ours. Each tentacle has its own brain and can continue to live when separated, at least for a while. The nose/mouth complex of a human (taste and smell) is in each suction cup ranged in rows down the arms: they taste with those suction cups but also can vary the suction through a little hole in the center and can fold themselves enough to pinch up small things, one cup separate from another. When they are handed the little fish or crab they eat, they accept it at the tip of the tentacle, and then pass it down the “arm” to the mouth which is a venomous beak. Their siphon can blast a person with water. When they “ink” with a cloud of obscuring darkness, they need to leave because it will suffocate them as well as their enemy.
Sy explores all this with adventures, including her own struggle to learn to scuba dive, and with her empathic reaching out and sharing the reaching out with others. She picks up on a multi-armed starfish that lives in the same tank as the octopus and which has NO BRAIN AT ALL, but constantly tries to sneak over to steal the octo’s fish, except that it gets hosed with a blast of water from the octo. It has no eyes, nor ears, so it must be picking up its sensory information from molecules in the water or maybe vibrations. The starfish is “thinking” — or at least reacting — with its whole body.
Somehow, that’s easier to understand than eight brains. How do they interact to achieve consensus? Sometimes it has been observed that an octo seems to have dissension in the ranks: some arms want to retreat and some arms want to advance. Octo’s also have favorite tentacles, something like being right-handed.
From wikipedia: “Fish intelligence is "...the resultant of the process of acquiring, storing in memory, retrieving, combining, comparing, and using in new contexts information and conceptual skills" as it applies to fish. According to Culum Brown from Macquarie University, "Fish are more intelligent than they appear. In many areas, such as memory, their cognitive powers match or exceed those of ‘higher’ vertebrates including non-human primates.” All bony fish have a hippocampus.
“Fish hold records for the relative brain weights of vertebrates. Most vertebrate species have similar brain-to-body mass ratios. The deep sea bathypelagic bony-eared assfish, has the smallest ratio of all known vertebrates. At the other extreme, the electrogenic elephantnose fish, an African freshwater fish, has one of the largest brain-to-body weight ratios of all known vertebrates (slightly higher than humans) and the highest brain-to-body oxygen consumption ratio of all known vertebrates (three times that for humans).
The fancy language (bathypelagic and electrogenic) refer to the depth in the ocean they occupy and what their source of energy might be. By the time discussion turns to things like “electrogenic” the real subject is ions and atomic dynamics in molecules. But those esoteric subjects are what explain how brains work, all those acquiring, storing, retrieving, combining, comparing and using functions, interacting through the various evolved cells and their structures.
One whole category of research is called “the Hippocampal Indexing Theory. It’s about those two little seahorse-shaped blobs just above the ears (inside— you can’t see them) which we’ve known for a long time are about memory. This field of study wants to know how it is that a particular smell, slant of light, tone of voice, can summon up a strong memory of a whole situation. So now I want to know whether an octopus has a hippocampus or eight hippocampuses or what precursor of a hippocampus might be like. The animals clearly do remember.
PZ Myers, writing in “Pharyngula” says: “We know that the octopus is amazingly smart. They are capable of associative and observational learning, they are curious and adaptive, and can invent new solutions to problems. They have a large brain relative to their body size, containing about 500 million cells, and they have condensed the classically distributed invertebrate central nervous system into a dense, discrete brain. One of the problems that stymied Young was that, rather than retaining the very large and accessible identifiable neurons we associate with invertebrates, the cephalopods have paralleled the vertebrates, microminiaturizing neurons to pack more cells into a given space. They’ve also built layered structures into their brains, and thrown the tissue up into folds that increase surface area, much as the vertebrate cortex has.”
It appears that a part called the vertical lobe handles long-term memory, similar to the hippocampus. “What does the VL do? Octopuses are tough and resilient, and as it turns out you can do some fairly invasive surgeries, stitch them up, and they recover just fine. The VL can actually be extirpated, and VLless octopuses, once they’ve got over the surgery, seem perfectly normal in swimming, feeding, and other ordinary behavioral functions. Deficits show up, though, when they are tested on learning and memory tasks: long term memory function is lost, and learning is greatly impaired. The VL and the median superior frontal lobe (MSF) together form a structure that is functionally analogous to the vertebrate hippocampus.”
“The findings emerging from recent electrophysiological studies in the octopus suggest that a convergent evolutionary process has led to the selection of similar networks and synaptic plasticity in evolutionarily very remote species that evolved to similar behaviors and modes of life. These evolutionary considerations substantiate the importance of these cellular and morphological properties for neural systems that mediate complex forms of learning and memory. In particular, the similarity in the architecture and physiological connectivity of the octopus MSF-VL system to the mammalian hippocampus and the extremely high number of small interneurons in its areas of learning and memory suggest the importance of a large number of units that independently, by en passant innervation, form a high redundancy of connections. As these features are found in both the octopus MSF-VL system and the hippocampus, it would appear that they are needed to create a large capacity for memory associations.”
Comparisons are a strong scientific method of investigation. Odious as comparisons between the worth and accomplishments of people, including the scientists, may be, looking for difference and sameness can reveal much information. So the octopus, which has evolved with no skeleton at all (it cannot develop Avascular Necrosis which in humans causes bones to disintegrate since it has no bones) might possibly reveal something about how to cure bone diseases.
In the meantime Sy and her friends create attachment and intimacy with creatures pretty much like silk scarves afloat in sea water with long arms buttoned with rows of suction cups and eyes they can pop up out of their heads to look at us. What they see makes them change colors and skin patterns, a sight-vocabulary that Sy learned. The original divergence of species comes back together in a confluence of interactions.