What Does the Octopus Strikes Again Mean
In one case upon a time, equally a young undergraduate, I took a course in neurobiology (which turned out to be rather influential in my life, but that'due south some other story). The professor, Johnny Palka, took pains at the start to explain to his class full of pre-meds and other such riff-raff that the form was going to study how the encephalon works, and that we were going to be looking at invertebrates almost exclusively—and he had to carefully reassure them that flies and squid really did have brains, very skilful brains, and that he nearly took information technology as a personal offense when his students unsaid that they didn't. The lesson was that if you lot wanted to acquire how your encephalon worked, oftentimes the well-nigh fruitful approach was an indirect one, using comparative studies to work out the commonalities and differences in arrangement, and try to correlate those with differences and similarities in function.
At about that time, I also discovered the work of the bang-up physiologist, JZ Young, who had done a great bargain of influential work on the octopus every bit a preparation for studying brain and beliefs. (Young, past the way, went by the breezy name "Jay-Zed", and there you lot have some other clue to my affectation of using my first and eye initial as if it were a proper proper noun.) It was around so that I was developing that peculiar coleoideal fascination a few of the readers here might have noticed—it was born out of an appreciation of comparative biology and the recognition that cephalopods represented a lineage that independently acquired a large brain and complex behavior from the vertebrates. To sympathize ourselves, we must comprehend the alien.
Young'south attempts to understand mechanisms of learning in memory in the octopus were premature, unfortunately—they take very complex brains, and nosotros made much faster progress using simple invertebrates, like Aplysia, to work out the nuts first—but it's still the subject of ongoing research. I was very pleased to come across a general overview of the octopus brain in The Biological Bulletin.
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 organization 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 accept paralleled the vertebrates, microminiaturizing neurons to pack more cells into a given infinite. They've also congenital layered structures into their brains, and thrown the tissue upwardly into folds that increment surface area, much equally the vertebrate cortex has.
And so what does an octopus brain expect like? Superficially, cipher like ours.
(click for larger paradigm)
The slice training and the basic circuitry of the MSF-VL system. A sagittal section in the cardinal encephalon of octopus showing the sub- and supraesophageal masses. Note the location of the vertical and median superior frontal lobes.
Right away, y'all should notice ane major peculiarity: the gut runs through the middle of it, separating the brain into a supra- and sub-esophogeal ganglion. Expect at it again, though: there are lobes and nuclei and tracts, and even without knowing annihilation nearly function, you can tell that this is a modular brain of considerable complication. Details are unlike, but the key matter is that nosotros run into specialized subunits emerging—processing centers that carry out dedicated tasks.
This newspaper focuses on one detail surface area, the Vertical Lobe, or VL, which is at the top of this image. Hither'due south a closeup:
(Summit) An image of a slice used in the physiological experiments. A sagittal slice from the medial role of the supraesophageal brain mass showing the vertical lobe (VL) and median superior frontal lobe (MSF) located dorsally to the median junior frontal (MIF) and subvertical (SV) lobes. (Bottom) The area within the white rectangle in acme figure with a superimposed circuitry schema. MSF neurons (blueish) innervating the VL via the MSF tract are shown schematically, as are the amacrine cells (yellowish), which synapse onto the big efferent cells (cherry-red).
What does the VL do? Octopuses are tough and resilient, and as it turns out you tin exercise some fairly invasive surgeries, sew them upward, and they recover just fine. The VL can really 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 upwardly, though, when they are tested on learning and retention tasks: long term memory function is lost, and learning is greatly impaired. The VL and the median superior frontal lobe (MSF) together form a construction that is functionally coordinating to the vertebrate hippocampus.
They also exhibit a microstructure of a sort nosotros see over and again in the vertebrate encephalon: a matrix of parallel fibers produced by many small cells, a set of input fibers (the MSF tract) crossing them orthogonally, and a minor set of large output neurons upon which all this arrayed action converges. Information technology'southward an elegant way to set up a huge number of synaptic connections and sample from a large field of possibilities, independently evolved in the octopus, and therefore may represent an optimal mechanism for generating behavioral flexibility. Again, there are differences in the details; octopus neurons, like many other invertebrate neurons, do not involve the cell body in generating electrical activity (very much unlike our neurons), and there are certainly substantial differences in the molecular biology and pharmacology of the channels involved. The hit features, though, are the convergences, which tell us what properties of a neuronal array might exist necessary for learning and retentiveness.
The findings emerging from recent electrophysiological studies in the octopus advise that a convergent evolutionary process has led to the pick 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 compages and physiological connectivity of the octopus MSF-VL system to the mammalian hippocampus and the extremely high number of pocket-size interneurons in its areas of learning and retentiveness suggest the importance of a large number of units that independently, by en passant innervation, form a high redundancy of connections. Every bit these features are found in both the octopus MSF-VL arrangement and the hippocampus, it would appear that they are needed to create a large capacity for memory associations.
Even something as specific as the neurobiology of learning and memory benefits from the evolutionary approach. By comparing unlike systems, we tin can place the commonalities linked to role, and thereby come closer to finding generalizable rules and principles rather than the usual welter of details.
Hochner B, Shomrat T, Fiorito G (2006) The Octopus: A Model for a Comparative Analysis of the Evolution of Learning and Memory Mechanisms. Biol. Balderdash. 210: 308-317.
Source: https://scienceblogs.com/pharyngula/2006/06/30/octopus-brains
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