ANDRZEJ KRAUZEThis issue devoted to hearing research completes our five-year tour of the “classical” Aristotelian senses: taste, touch, smell, sight, and hearing. Each year, a different sense commanded our immediate attention; we saved hearing for last because we thought hearing research might be less interesting. Boy oh boy, were we wrong. The more we surveyed the current state of the field, the more excited we got.
So here (hear!) you have it. Our own behind-the-scenes need for a primer to consult on how a sound turns into a nerve impulse led to a beautiful two-page infographic of the auditory pathway. Hidden deep in the human inner ear, encased in bone, is the amazing organ of Corti, a spiral staircase nearly an inch long, studded with sensory cells that deliver sound to our brains in a frequency-specific fashion. To get a fuller sense of auditory dynamics, check out the online offerings selected to enhance this issue, including an animated tour of the middle and inner ear responding to bars from a Beethoven symphony.
In “Aural History,” Geoffrey Manley lays out how the middle and inner ears of terrestrial vertebrates evolved. Despite branching off from a common ancestor some 300 million years ago, before the evolution of a dedicated hearing organ, the three extant lineages of amniotes—lepidosaurs (lizards and snakes), archosaurs (crocodilians and birds), and mammals—all process sound in very similar ways at the physiological level. It’s a remarkable example of convergent evolution, with each lineage now possessing a bony middle ear to amplify sound and a delicate auditory papilla outfitted with sensory cells topped with what look like weird haircuts, appropriately dubbed hair cells.
Basic research is edging closer to translation into new therapies for hearing disorders.
Studying the actual workings of inner-ear hair cells in vivo is hampered by the cells’ inaccessibility, and the complicated anatomical arrangement of the organ of Corti makes in vitro studies challenging. Researchers have devised a number of clever techniques to align in vitro studies with in vivo reality and to search for hints on how to restore function to damaged cells. “Inner Ear Cartography” describes an elegant spatial mapping strategy based on gene expression in nine cell types of the hearing organ. Two recent research reports use hair cells from the vestibular system (from which hearing sensory cells evolved) to get a bead on hair-cell regeneration, a phenomenon that has been lost in mammalian hearing organs but that researchers hope could be reactivated (here and here). A longer literature report describes discrepancies that arise as a result of probing function under in vitro conditions.
Encouragingly, basic research is edging closer to translation into new therapies for hearing disorders. “The Sounds of Silence” reports on treatments for tinnitus, a persistent ringing in the ears for which no drug currently exists, and whose maddening quality Edgar Allan Poe captured so well in his lines about “the tintinnabulation of the bells, bells, bells.” And in “Hearing Help,” Kate Yandell explores the small molecules and gene therapies on the horizon for patients suffering from hearing loss. Some researchers are even hoping to regenerate inner-ear hair cells or to enhance their connections with sensory neurons. In an opinion piece, Bernd Fritzsch sounds a cautionary note, however: building a hearing organ from scratch may never be possible.
The entire Notebook section is devoted to behind-the-scenes stories about hearing research in the lab and in the clinic. “The Ears Have It” profiles the prolific career of James Hudspeth, and the issue is peppered with quotes and research from scientists who spent time in his lab.
One sense per year means updates are in order, but before revisiting the classical five, we have something “extra” in store for 2016.
Mary Beth Aberlin Editor-in-Chief