“To understand ourselves, we must embrace the alien.” – PZ Meyers
One difficulty in understanding consciousness is the fact that we know of only one species that certainly possesses it: humans. A new article by Jennifer Mather suggests that octopi may also possess consciousness, despite the vastly different architecture of their brain. If two very different neural architectures can both support forms of advanced cognition, then the similarities between them may help clarify the computational requirements for intelligent behavior.
Octopus brains are striking different from those in primates (for example, 3/5 of all their neurons are actually outside the brain). They also seem to have evolved a brain almost completely independently from those in mammals. Despite these differences, octopus brains also have ventricles, lobes, nuclei and in some cases regions that appear homologous in architecture to human learning and memory areas, such as the hippocampus.
Mather’s article on cephalopod consciousness takes a more behavioral approach to understanding octopus intelligence. Although the physiology of octopi brains is increasingly well-understood, the relationship between octopus brains and their behaviors – indeed, even the breadth of their behavioral repertoire alone – is fairly unexplored. Mather reviews several interesting pieces of evidence relevant to this point:
- Cephalopod brains show bilateral symmetry, lateralization of function, and similar impairments as humans when the homologue of the corpus callosum is severed (the tissue connecting the two hemispheres). For example, octopi trained to make a choice with one eye can transfer this knowledge to making the same decision with the other eye, even if the corpus callosum homologue is severed after training. This ability is not present if the corpus callosum homologue is severed before training.
- Like humans, octopi seem to have a dominant eye, and dominant or preferred arms. Mather suggests this is indicative of a “central processor,” thought to be important in some theories of consciousness (including “global workspace” theory).
- Octopi spend much of their time in a sleep-like state in which the pupils narrow and they are unresponsive to external stimulation. Sleep deprivation of octopi apparently leads to a simliar “sleep rebound” as in humans.
- Studies of octopus memory suggest at least a 2 cognitively distinct forms of memory, corresponding to short and long-term memory (a well-established division in the human literature). For example, Mather presents evidence that young cephalopods can remember for short periods of time (~5 minutes) but not longer periods of time until they are older, perhaps corresponding to the delayed development of the vertical lobe region (the same region thought to be homologous with the hippocampus in humans).
- Spatial and episodic memory also seems relatively well-developed in octopi, such that they do not need to retrace their outgoing path to return to their shelters (in contrast to many molluscs).
- Aging seems to have similar effects on cognitive capacity in cephalopods, such that older organisms demonstrate slower and more variable motor, sensory and learning performance.
- Octopi show surprising behavioral flexibility; for example, a “exhalant water jet” common to octopi and molluscs has been exapted by octopi for use in locomotion, the construction of shelters, and even what appears to be play. Note that dolphins, a cognitively advanced vertebrate, have also been observed to play and teach games with age-appropriate rules, although play behavior may be somewhat common among animals.
- Like mammals, octopi are better at discriminating vertically-oriented shapes than horizontally-oriented ones (although this likely reflects optimization for the sea floor, just as in mammals it may reflect optimization for upright walking). They can also be trained to discriminate mirror images from one another as well as generalize to images that are rotated 90 degrees, showing remarkable flexibility (generalization and discrimination are in some ways computationally opposed).
- Octopi also seem to suffer from proactive interference in training, just like humans, such that learning to attend to one feature of a stimulus impairs later learning about a second feature of the stimulus.
- Octopi show strategic and flexible organization of manual hunting behaviors, beginning with the least energy-expending methods for opening clams or snails and movinig on to more sophisticated techniques involving drilling through the shell, the injection of toxins, and flexible avoidance of novel man-made obstacles on the shells (such as dental cement and metal wiring). Contrary to some reports, octopi have also learned to open jars in order to access food inside, provided they are given chemical cues that the jar contains food. [Anecdotal reports also describe octopi climbing onto the decks of ships, opening containers of caught fish, and having a snack.]
- Octopus performance on traditional behavioral tests of theory of mind is difficult to evaluate, since octopi are primarily solitary animals. The classic “mirror test” of consciousness is also inconclusive since octopi seem relatively unreliant on vision. Squid, on the other hand, are more social animals and are apparently more reliant on vision (considering they have relatively sophisticated real-time control of the pigmentation of their skin. Some have proposed that these two feature might permit for the emergence of language among squid. Sure enough, patterns of skin pigmentation have been to have a lexical but not grammatical communicative structure (i.e., skin color seems to convey detailed information about current sexual or emotional states, without seeming to have a rule-like structure for how those signals can be combined).
These points demonstrate remarkable cognitive skills in a species with a profoundly different neural architecture than our own. Further exploration of the relationship of cephalopod and primate behavior, as well as the underlying physiology, may ultimately result in a platform-independent understanding of how the brain gives rise to advanced cognition.
Mind Games: Humans, Dolphins and Computers
Correlating Brains, Bodies and Behaviors
Shared Intentionality in Human and Primate Cognition
Dolpins: Stupid or Smart? A Summary and Synthesis