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Comb Jellies take on 150 years of the Neuron Doctrine

When it comes to the nervous system, you might think we’ve got the basics down. After all, it’s been over a century since the great Santiago Ramón y Cajal proposed the neuron doctrine, which basically said that the nervous system is made up of individual, discrete cells called neurons. As you may recall from our neuropharmacology experiments, Ramón y Cajal argued for discrete cells (neurons), while Gogli thought that the brain consists of groups of continuously connected cells (reticulum). Santiago’s hypothesis, known as “The Neuron Doctrine,” was later confirmed by the invention of the electron microscope, which let us see these neurons and their connections in all their glory.

But now it looks like the fight is still on! New research on ctenophores, those weird, squishy marine critters that look like a cross between a jellyfish and a feather duster, is shaking up the status quo.

The importance of these jellies cannot be overstated. As one of the first animal groups to branch off on the evolutionary tree, studying ctenophores can provide us with clues about the very origins of animal life. And while these guys have no brains, they do have a nervous system consisting of a “neural net” – a type of nervous system organization that is very understudied. Could it be that a nervous system evolved twice, independently, in our animal ancestors? That’s the question these researchers were asking.

To get their answers, a group of European researchers led by Dr. Kittelmann at Oxford Brookes University turned to high-pressure freezing-fixation techniques and a method called serial block face scanning electron microscopy (try saying that five times fast!). This gave them a stunning, 3D view of the ctenophore’s nerve net. And what they found was quite unexpected and they shared it with the world in a recent Science paper [Burkhardt et al., Science 380, 293–297 (2023)].

Unlike our own nervous system, which comprises separate neurons connected by synapses, the ctenophores’ nerve net looked more like a reticulum – a continuous network of interconnected cells. Instead of discrete neurons with synapses (small gaps between the cells), the ctenophores have a nerve net where all the nerve cells seem to be part of one, big supercell. It’s kind of like comparing a bunch of individual houses to a giant apartment complex. As seen in their figure below, the 5 separate neurons of the nerve net are actually all fused together (highlighted in white asterisks for links between neuron 1 and 2).

Neural Net with connections

In the world of nerve nets, this is a pretty big deal, as it suggests that there’s more than one way to build a nervous system and that different animals might have taken different paths in their evolution to encode information and guide behaviors. The ctenophore nerve net is not just a simple precursor to our own complex brain but a complex and unique structure in its own right.

This opens up a whole new perspective on how nerve nets and nervous systems function and evolve, and reminds us that even long-held truths in science can change upon new evidence. So next time you see a ctenophore, don’t just marvel at the beauty of the squishy color-changing blob. You can also admire its nervous system that’s every bit as complex and fascinating as ours, just in its own, unique way. And who knows? Maybe we’ve got more in common with these jellies than we think. There’s so much more to be discovered!

Chilean High School Interns Say Goodbye (For Now!)

Editor’s note: This is Part II. You can read Part I here.


Hello, I am Danae Madariaga, a senior at Alberto Blest Gana high school. I have participated in a data collection project with Etienne, Tim, and Derek for three months. Throughout this time, I have learned many things such as the use of Google Colab to analyze my data that I uploaded to the cloud. This makes it easier for scientists from around the world to analyze my data as well.

Really though, the most important thing that I have learned is that being a scientist is not easy! It is a very hard job that requires perseverance and patience. I have also learned how to optimize my time to perform my experiments in a consistent manner. Working with Backyard Brains was my very first job and a very pleasant experience, especially with all the new tools and plants I have now!

chilean high school seniors say goodbye
My Home Experimental Setup with Basil Plants and Venus Fly Traps

Engineering Cyborgs: The Gastronauts Podcast With Greg Gage

Backyard Brains has just added another feature to our ever longer list of media appearances! This time, our co-founder and CEO, Dr. Greg Gage, talked for The Gastronauts, Duke University’s monthly seminar and podcast series. This seminar is being organized by researchers passionate about gut-brain matters. But when one invites the driving force behind Backyard Brains, one has to squeeze in an occasional cockroach too!

If I were God and wanted to make the perfect brain machine interface, I’d have made a cockroach,” says Greg in the podcast. Indeed, he adds, underneath a roach’s antenna, there’s a little tube where a wire fits perfectly.

But there’s more to our mission than creepy crawlies. This info doesn’t get heard every day: over 46,000 people have heard a spike for the very first time in their lives, using our DIY neuroscience gear. And this is just according to the cold, hard numbers that we have in writing. In reality, it probably never ever happened for a SpikerBox to be used by a single person. More often than not, our SpikerBoxes go to schools and research institutions where each of them gets to play spikes for years and generations, into many an curious ear. That could easily bump up the number to at least four or five the figure!

Our co-founder also talked about a variety of conceptual and engineering ideas and tips that came to us from high-schoolers who were using our gear in their school labs. For example, the cockroach-machine interface we made had a major flaw: before long, the cockroach would adapt to stimuli and just start living with it. Why not play music into it? Indeed, it worked up to a point. “But even more successful were little blinders that made them adapt slower as they couldn’t integrate other info that was coming – a brilliant idea that we never came up with! Then we implemented a randomization function into our stimulus,” Greg recalls.

There was also mention of our new book, which came as a culmination to our decade-long work on neuroscience experiments for everyone, but also some exciting new projects that are currently being cooked in the BYB kitchen.

Find the podcast episode below!