An array of touch sensors on bat wings may have helped these little insect eaters become the agile masters of the night sky that they are. According to findings published in Cell Reports this week, those ultra-sensitive receptors send tactile information to the brain, triggering split-second wing adjustments midair as needed.
Bats are the only mammals capable of powered flight, reaching speeds of 32 kilometers an hour (20 miles per hour) and accomplishing aerial acrobatics that man-made aircrafts can’t compete with. Check out this video of an echolocating bat snatching a mealworm in the air like it’s no big deal. To catch bugs and maneuver around obstacles in three dimensions while flying, bats must rapidly integrate all sorts of sensory information. Bat hearing and bat vision have been studied extensively, but bat touch has been long overlooked -- despite how they also use their wings to climb cave walls, handle food, and cradle their pups. Researchers recently discovered that the wing skin is covered in microscopic hairs that are stimulated by airflow, and that these hairs help bats control their speed and make those quick turns.
Now, to investigate how bats use these sorts of tactile feedback to enhance flight control, a team led by Cynthia Moss of Johns Hopkins and Columbia University’s Ellen Lumpkin examined the touch-sensitive receptors of big brown bats (Eptesicus fuscus). Using a tracer dye in the wings and staining the skin, they were able to map the distribution of the sensors. Their positioning suggests that different parts of the wing send different types of sensory feedback to the brain: Cells between the fingers respond to stretching of the skin and wind direction changes, while cells clustered at the base of the tiny wing hairs specialize in detecting airflow changes and turbulence.
Then, when the team puffed air at the little hairs to ruffle them, neurons in the bat's primary somatosensory cortex responded with sparse, but precisely-timed bursts of activity. The neurons responded similarly when the researchers touched the wing lightly -- indicating how airflow and tactile stimulation activate the same neural pathways. To the right is an image of bat sensory neurons.
Surprisingly, the team also discovered that neurons in the wing skin connect to both higher and lower parts of the spinal cord. The latter typically innervate the trunk of the animal, not the forelimbs. This strange circuitry seems to reflect the motley roots of the bat wing. “It gives us insight into how evolutionary processes incorporate new body parts into the nervous system," first author Kara Marshall of Columbia explains in a university statement.
Lumpkin adds: “This study provides evidence that the sense of touch plays a key role in the evolution of powered flight in mammals.” Next, the team wants to follow the sensory circuits from the skin to the brain, and maybe one day, the work will help us design planes that can sense and adjust to the environment. [Via Columbia & Johns Hopkins]
Images: Jessica Nelson (top), Kara Marshall/Columbia University Medical Center and Ben Falk/John Hopkins University (middle)