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Invertebrates: A Vastly Different Brain Structure Can Be Remarkably Efficient

Have you ever wondered about how an alien’s brain works? What kind of information-processing system they may have and how it may differ from ours? There is no need to look any further. The answers to these questions can be found much closer to home, in insects and other invertebrates.

Insects and humans have evolved quite differently, and thus they have a very different kind of neural system. Insects, jellyfishes, octopuses, and many other invertebrates have a very sophisticated nervous system, they display remarkably complex behavior, learning abilities, and level of intelligence. Yet, many of them lack the kind of brains we have. That is, they lack a centralized decision-making system.

If we chart the evolution of the neural system, we can see that the earlier neural networks were more diffuse. The collections of neurons called ganglions make most of decisions locally (non-vertebrates have several ganglions), while some central decisions like the direction of movement of the whole body are made more democratically. In fact, it is still not fully known when the centralization of the nervous system started to take place.

It is well accepted that Cnidarians have one of the most primitive neurological systems. This is from where other living beings evolved in terms of neural capabilities. Organisms of this evolutionary branch, like jellyfish, are still common today. Now it is known that their neural system is quite complex and has more intellectual capabilities than we had thought.

A decentralized or diffuse nervous system has some fantastic capabilities. Some insects like Drosophila flies can stay alive for many days after being decapitated. They do not only survive without the head, they can fly, walk, and even copulate. Cockroaches would be able to remember things even if their brain was removed.

Although diffuse nervous systems are more primitive, it does not imply the lack of intelligence. An example of a decentralized, large, and at the same time incredibly complex nervous system is in the octopus. Octopuses have the majority of neurons or collections of neurons (ganglions) located in their arms (tentacles). The arms of an octopus can do lots of things independently from each other; they can perform basic motions and they can touch or taste without any interference from the brain. Although octopuses have nothing common with vertebrates when it comes to neuroanatomy, yet they can learn things, recognize subjects, and perform complex tasks.

We have erroneously come to see brain size as a measure of intelligence in species since we know that most representatives of the animal kingdom, particularly non-mammals, have far smaller brains than ours. But the correlation between brain size and intelligence is not linear. Just think of whales that have a brain weighing 9 kg and containing 200 billion neurons. A typical human brain, for comparison, is around 1.5 kg in weight and has 80 billion neurons. This is proof that not all kind of intellectual activities depend on brain size or the number of neurons.

This lack of a direct correlation explains why some insects are more innovative than us or any other higher animals when it comes to socializing, forming colonies, or even learning from each other. Colonies of bees and ants have very complex social structures, where various members have clearly divided tasks. They have a complicated system of communicating with each other. They even have clear labor division, which includes the casts of slaves, farmers, and warriors. What is amazing is that such complex activities are achieved with the help of just a few million neurons.

Now we understand that the nervous system doesn’t have to be centralized to function efficiently, and different forms of nervous systems have their pros and cons. Further, we know that neither the brain volume nor the number of neurons is an indicator of intelligence. However, we have beein maintaining the thought that, at least for handling, larger brain volumes of information need a larger number of neurons. But even this view is under revision now.

Many complex behavioral reactions and responses can rely on just a few neurons and be independent of the brain. Think of reflexes such as the pain response that is a function of ganglions and not the brain. We are learning to appreciate the value of our gut feeling, as the gut has an enormous amount of neurons playing a much broader role in health.

Understanding the existence of entirely different kinds of cognitive systems, neural systems, or information processing systems has many implications for human health. It forces us to look at our bodies from a different angle. It is entirely possible that a certain degree of non-centralized intelligence, and maybe even non-neural information processing, exists in our body.

An excellent example of diffuseness of body systems is our endocrine system. The concept that endocrine functions are limited to some specific organs is becoming obsolete. We are now talking about diffuse endocrinology, as every organ and tissue secretes some endocrine hormones with various effects, be it the gut or fat. Similarly, many researchers are now talking about diffuse neuroendocrinology, as the two systems are very well connected.


Ameri, P., & Ferone, D. (2012). Diffuse endocrine system, neuroendocrine tumors and immunity: what’s new? Neuroendocrinology, 95(4), 267–276. doi:10.1159/000334612

Arendt, D., Denes, A. S., Jékely, G., & Tessmar-Raible, K. (2008). The evolution of nervous system centralization. Philosophical Transactions of the Royal Society B: Biological Sciences, 363(1496), 1523–1528. doi:10.1098/rstb.2007.2242

Gagliano, M., Vyazovskiy, V. V., Borbély, A. A., Grimonprez, M., & Depczynski, M. (2016). Learning by Association in Plants. Scientific Reports, 6, 38427. doi:10.1038/srep38427

Koizumi, O. (2016). Origin and Evolution of the Nervous System Considered from the Diffuse Nervous System of Cnidarians. In The Cnidaria, Past, Present and Future (pp. 73–91). Springer, Cham. doi:10.1007/978-3-319-31305-4_6
Kuehnle, I., & Goodell, M. A. (2002). The therapeutic potential of stem cells from adults. BMJ?: British Medical Journal, 325(7360), 372–376.

Image via mineev_88/Pixabay.

Source: Brain Blogger