A Map of the Octopus’ Visual System Reveals Their Own Vision Solution: ScienceAlert

A valiant effort to map the optic lobe of the octopus brain cell by cell has revealed a visual system with remarkable similarities and differences to our own.

The parallels are particularly interesting because they speak of the seemingly coincidental nature of convergent evolution.

Humans and octopuses diverged from a common ancestor 500 million years ago, and yet the way our respective visual systems have evolved to solve the same problems is eerie. Despite our different morphologies, lifestyles and habitats, vertebrates and octopuses independently developed a pupil and a lens that guides light onto a retina, for example.

Soft-bodied cephalopods — cuttlefish, octopuses and cuttlefish — have the largest brains of any invertebrates, with two-thirds of their central processing tissue reserved for vision.

As you’d expect from all that space, these ocean creatures have really good vision, even in the dark. The skin of an octopus contains the same pigment proteins as his eyesallowing its dermis to “see” the details of its environment and camouflage it accordingly.

The current study by researchers at the University of Oregon is the first to fully map the octopus’s visual system. It required an analysis of more than 26,000 cells collected during the dissection of two juvenile cells California two-spot (Octopus bimaculoides) octopuses.

Although the brains of these young octopuses were fully functioning, they appeared to be growing. In fact, nearly a third of the neurons scattered throughout the visual lobes looked like they were still developing.

When researchers found the sequences of the cephalopod cells, they found four main populations, each of which gave off a different chemical signal — some released dopamine, some released acetylcholine, some released glutamine, and others signaled with both dopamine and glutamine. .

These neurotransmitters are also seen in the brains of vertebrates, such as ours, but there were several smaller neuron clusters in the cephalopod brains that expressed unique chemicals.

For example, a ring of cells around the lobe of the eye was found to produce octopamine, a neurotransmitter closely related to a hormone in our body called norepinephrine.

What exactly octopamine does in octopuses is a mystery that needs more research to solve. However, it is known to be active in the brains of fruit flies when they fly, and is important in many other invertebrates for functions related to preparing their bodies and nervous systems for action.

This new map of the octopus brain could help future efforts. Researchers identified several genetic transcription factors and signaling molecules unique to octopuses, which likely help shape neural development in one way or another.

Further studies could remove or dampen these factors to find out their possible role in the cephalopod brain.

“The atlas we present here provides a roadmap for such studies, and more broadly offers a path forward to cracking the functional, developmental and evolutionary logic of the cephalopod visual system,” the authors said. to write.

Similar to vertebrates, the octopus’ visual system is structured in layers, but not in the same way as ours. The diversity of cell types and the way they are organized in the brains of cephalopods is fundamentally different.

“At the obvious level, the neurons don’t map to each other — they use different neurotransmitters,” explains biologist Cris Niell of the University of Oregon.

“But maybe they’re doing the same kind of calculations, just in a different way.”

One of the biggest questions is how the visual system of cephalopods develops. Octopuses spend years growing huge brains, but how does information from the retina help direct that growth?

In vertebrates, photoreceptors in the retina do not connect directly to the brain. Instead, they relay messages to other neurons. But in cephalopods, photoreceptors connect directly to the optic lobes of the brain.

Future work is needed to investigate how these direct messages affect the development of immature neurons, and how so many immature neurons eventually integrate into a mature visual system.

Niell and his colleagues are now continuing their work to map the remaining third of the octopus brain.

The study is published in Current Biology.