(Describer) Science Out Loud. Red dots grow and shrink in waves.

(female) This looks like an artist made it, but it wasn't made by an artist or even a person. It's the work of a squid.

(Describer) One swims underwater. Another lies on white rocks.

Here is a longfin inshore squid caught off the shores of Woods Hole, Massachusetts. When I approach him, he turns red, signaling his aggression. His brain has total control over what his skin is doing. Inside the squid skin are small pouches of pigment called chromatophores.

(Describer) The dots.

Each chromatophore is pulled opened by tiny muscles. To turn red, neurons from the squid's brain send signals to these muscles, which pull open all of his chromatophores at the same time. Here, we've cut nerves that go to the small area on the squid's side and the chromatophores go quiet, which you'd expect since we've disconnected the skin from the brain. But they don't stay quiet. Days later, this happens.

(Describer) Waves of color move.

This squid has control over his skin. This one doesn't. But somehow these chromatophores are opening and closing anyway. Let's take a closer look under the microscope.

(Describer) The dots are shown more closely.

The chromatophores open and close in beautiful waves of color. These patterns can seem pretty complicated. Some people think octopuses use patterns like these to mesmerize their prey. Why do these intricate displays emerge on the squid's skin even after it's been disconnected from the brain?

(Describer) By a laptop...

First, I wanted to measure how chromatophores grow and shrink. I wrote a program that measures each chromatophore's size over time.

(Describer) ...shown on the laptop.

Let's add color to see what's happening. In this program, I've colored the open chromatophores red and the closed ones blue. Look at what this chromatophore's neighbors do right before it opens.

(Describer) They briefly change color.

Right before it opens, its neighbors open. Let's see that again.

(Describer) The neighbor dots change first.

What rule could govern this behavior?

(Describer) The squid is shown again.

You might say a chromatophore opens after its neighbors open, but is it that simple? I'll write a program to simulate the squid skin using just that one rule.

(Describer) She types in fast-motion.

Here it is.

(Describer) She brings back the dots.

The small dots represent closed chromatophores, and the larger dots represent open chromatophores. Let's run the program.

(Describer) The small dots gets bigger and stay that way.

This doesn't look right. In the real squid skin, the chromatophores open and close over and over again. But in the simulation, they open once and stay open. What if we add another rule? Let's look at the squid again.

(Describer) The chromatophores keep opening and closing.

What about this? After a chromatophore opens, it needs to wait before opening again. This need for pause is common in many cells, including neurons. It's called a refractory period.

(Describer) She types more code, and shows it.

Here's take two of the simulation. First, the chromatophore opens after its neighbors open, and I've added an extra rule: right after the chromatophore opens, it needs to take a break.

(Describer) She points to the dots.

I'm starting with a line of open chromatophores and a line of chromatophores that are refractory underneath. They need a break before opening. Let's run it.

(Describer) Dots grow and shrink, forming a moving pattern like a spiral.

This looks even more like the real squid skin.

(Describer) They’re compared side-by-side.

Here's another simulation with three different colors of chromatophores. I've made the gray ones expand randomly. The yellow and red ones respond to their neighbors with different sensitivities. As you can see, the simulated patterns look very complex, even though they are governed by such simple rules. When we cut the nerves to some skin, the chromatophores acted like they had a mind of their own. They're really following two simple rules: listen to their neighbors and pause after they open. From these simple rules, mesmerizing patterns emerge. Even in our complex biological world, some of the most beautiful things can be explained by the simplest concepts.

(Describer) Title: Made with love at MIT. Accessibility provided by the U.S. Department of Education.

Accessibility provided by the U.S. Department of Education.