Octopuses: The behavior of octopuses is characterized by extreme curiosity, quick adaptation to most circumstances, superb vision, flexible arms (which are sometimes used to mimic other animals), and the ability to learn associatively. Although octopuses are invertebrates, when you normalize the number of neurons to body weight of various species, octupuses contain a ratio similar to that of vertebrates. However, they still have fewer neurons proportionally than mammals and birds.
The ganglionic masses in the octopus (and cephalopods in general) is greater than that of other invertebrates, which is thought to be due to evolutionary encephalization. This increased size decreased the distance between various brain regions and probably increased the speed of neural computation, making octopuses “smarter.”
Of the octupus’s ~ 500 million neurons, 120 to 180 lie outside of the brain capsule in the optic lobes, and 330 million or so lie in the nervous system of the arms, which are fairly autonomous. Only 40 to 50 million lie in the actual “brain”, which is usually less than 8 cubic cm.
Through lesion experiments, researchers have been able to confirm that the vertical lobe (VL) is essential to learning in memory. Octopuses whose VL have been removed retain motor function but will continue to attack a crab despite receiving electrical shocks, while octopuses with intact VL regions will learn to discontinue this behavior. The VL has about 25 million neurons, representing the majority of cells in the octupus brain.
The VL region receives most of its input from the sensory median superior frontal lobe (MSF), which has some axon tracts running through the VL. Small amacrine interneurons from the VL extend neurites which attach along the path of these axons. The interneurons extend to about 65,000 larger neurons, whose axons form the output of the VL.
This is similar to the interactions between Schaffer collaterals and pyramidal cells in the CA1 region of the mammalian hippocampus. The convergent evolution of these systems raises some interesting questions: 1) Is this redundancy of connections through en passant innervation crucial for molecular mechanisms of memory? and 2) Is a large number of small interneurons also essential for encoding memories?
Owls: Owls are an order of birds of prey, and thus are endowed with many characteristics typical of bird brains. Contrary to the conventional wisdom towards a “bird brain”, aves are generally quite smart and as indicated above, they have very high numbers of neurons in their brain once you normalize for body weight. They can learn by observation (or at least contagion), they can recall the exact location of a stored piece of food over a long period of time, and some species can recognize themselves in a mirror, which is one of the weaker criterions for conciousness. Evolutionarily, birds are the only living ancestors of dinosaurs, which makes them interesting to 8 year old kids everywhere.
One of the specialized aspects of owl brains is their ability to detect movement via their auditory system, which is especially useful for owls because they are nocturnal and cannot rely as much on vision. Witten et al recently studied this ability of owls and found that their auditory receptor field updates rapidly based on changes in the interaural time difference and interaural level difference for high frequency wavelengths. The model that the researchers built to account for the prediction allows the receptive field to predict sound movements about 100 ms in the future, but that it needs to listen to the sound for at least 500 ms before it can orient a proper response. I assume that a proper response would either be an attack (gobble gobble) or to orient its head toward the stimulus in order to be able to recieve better auditory feedback.
The neural correlate of this ability is the space map of the optic tectum. This is similar to sensory representation in humans, for whom motion induced perceputal effects are apparent not only in the auditory system but also for luminance and color aspects of the visual system. The predictive abilities in the owl’s auditory system is a microcosm of its nuanced intelligence.
This was inspired by CalTech’s question #2: “Discuss the major features of at least two very different nervous systems (i.e. jellyfish, locust, lamprey, octopus, owl, rat, monkey). In what ways might the features of each system affect neural processing?”. Feel free to discredit my answer or offer your own in the comments.
Hochner B, Shomrat T, Fiorito G. 2006 The octopus: A model for a comparative analysis of the evolution of learning and memory mechanisms. Biological Bulletins 310: 308-317. Link.
Witten IB, Bergan JF, Knudsen EI. 2006 Dynamic shifts in the owl’s auditory space map predict moving sound locations. Nature Neuroscience 9: 1439 – 1445. doi:10.1038/nn178.