Bats have always impressed scientists with their super-precise flying abilities, and a recent study shows the secret to these sharp turns and maneuvers is sensitive touch sensors in their wings that respond to the tiniest changes in airflow.
Almost a decade ago Cynthia F. Moss, professor in the Department of Psychological and Brain Sciences at Johns Hopkins University, got involved in a project that was one of the first to look at the function of microscopic hairs on bat wings. Her research team conducted both behavioral experiments and neurophysiological recordings on a group of bats.
"From the results of this first study we concluded these microscopic hairs embedded in the bats' wings are important for sensing airflow and play a role in flight control," Moss told HNGN.
The researchers had bats fly in a room and monitored them using sophisticated high speed video equipment that allowed them to record flight behavior through different sets of obstacles. For phase two of the tests, they removed the tiny wing hairs using a depilatory cream, and found the bats could still fly but their flight behavior was altered.
"The bats didn't make turns that were as sharp after the hair removal, and also after they approached obstacles they didn't slow down as much as they did before the treatment," Moss said.
During the neurophysiological experiments of the somatosensory cortex of bats, researchers pinpointed and recorded the activity of different neurons as various stimuli were applied to the wings, such as a light touch with a calibrated filament or bursts of air. The bats demonstrated responses to airflow in the somatosensory cortex that demonstrated selectivity for specific directions.
"So if we pointed the air in one direction we might get a strong response and if we pointed it in another direction we might get a weaker or no response at all," Moss said.
The team then did the same protocal they used in the behavioral experimen, removing the hairs from the bats' wings. After doing so, they observed that responses to airflow in the neurons of the somatosensory cortex disappeared. The neurons still responded to light touch, but their ability to register airflow via the stimuli from the hairs was gone.
Around the time this work was published, Moss met Ellen Lumpkin, a professor of somatosensory biology at Columbia University. The two began a collaboration involving some of Lumpkin's students in which they worked to characterize the wing receptors in brown bats, which are common in North America.
"The hairs themselves are like levers – so when they move, it stimulates the receptors. And our collaboration showed there are two classes of receptors that are associated with these hairs: Merkel cells, which are important for discriminating [details in touch], and lanceolate endings, which are commonly associated with hairs and are important for sensing hair movement," Moss said.
They found that bat wings had a large percentage of Merkel cells associated with the hairs. This phenomenon is seen in other animals, but never in such large proportions. The two uncovered evidence of other types of receptors that they believe play a significant role in sensing stretch in their wings. The researchers also found that neurons in the wing skin were connected not only to the upper region of the spinal cord, but also to the lower parts, which has not been seen in any other mammalian forelimb.
These fascinating new findings could shed light on the history of bat evolution as well as have applications in modern technology and aeronautics.
"The array of touch receptors that the bat uses to guide its flight combined with its ability to actually shape its wing could lead to new technologies that allow for more maneuverable aerial vehicles," Moss told HNGN.
In the future, the team hopes to drill down to the dorsal root ganglion, which contains cell bodies for the neurons linked to the sensors along the wing. The goal is to gain a better understanding of how information from different receptor types combine. They also hope to examine additional bat species to detect if similar and differing patterns in these sensors.
The research was published today in the journal Cell Reports.