Squid have hundreds more hair cells than scientists thought

Popular Science reports that researchers at Case Western Reserve University have found squid have hundreds more hair cells than previously known. Hair cells are sensory cells topped with bundles of hair-like protrusions. Scientists already knew squid had them on their heads and arms. The new work shows them spread across the body.

The researchers, whose study appeared in the journal Current Biology, used a technique called light sheet microscopy. A thin sheet of light illuminates one plane of a specimen at a time, allowing detailed 3D images with less tissue damage. They also produced the first full-body map of lateral lines on squid, which are features made up of hair cell clusters.

Why it matters for human ears

Human hearing depends on similar hair cells. Sound vibrations travel to the cochlea, a snail-shaped organ in the inner ear. The cochlea holds thousands of hair cells, each topped with tiny structures called stereocilia, or cilia. Their length matters: cilia are longer in areas that detect low pitches and shorter in areas that detect high pitches. That positioning helps each cell respond to a specific frequency. When sound vibrations move the cilia, the hair cells send signals through the nervous system to the brain, which turns them into sounds.

Squid appear to use the same basic setup to sense water movement. Like octopuses, they have cilia bundles on their bodies, and their survival may depend on detecting different frequencies of water movement, much as human ears pick up pitches.

What squid could teach us

The new study suggests squid may even regulate the length of their hair bundles to tune cells to different frequencies, the way human ears do. Fish lateral lines, by contrast, have hair bundles of the same length. That difference makes squid a promising animal for studying how hearing and hearing loss work.

Brian McDermott, a biologist and co-author of the study, said in a statement: "Often, when a child is born deaf or a hearing person loses their hearing, it is the hair bundle that has been damaged. So, studying the squid's hair bundle holds promise for understanding how hearing loss occurs."

• Brian McDermott
• Case Western Reserve University
• Current Biology
• hair cells
• hearing research
• squid