Functional role of airflow-sensing hairs on the bat wing

The wing membrane of the big brown bat (Eptesicus fuscus) is covered by a sparse grid of microscopic hairs. We showed previously that various tactile receptors (e.g., lanceolate endings and Merkel cell neurite complexes) are associated with wing-hair follicles. Furthermore, we found that depilation of these hairs decreased the maneuverability of bats in flight. In the present study, we investigated whether somatosensory signals arising from the hairs carry information about airflow parameters. Neural responses to calibrated air puffs on the wing were recorded from primary somatosensory cortex of E. fuscus Single units showed sparse, phasic, and consistently timed spikes that were insensitive to air-puff duration and magnitude. The neurons discriminated airflow from different directions, and a majority responded with highest firing rates to reverse airflow from the trailing toward the leading edge of the dorsal wing. Reverse airflow, caused by vortices, occurs commonly in slowly flying bats. Hence, the present findings suggest that cortical neurons are specialized to monitor reverse airflow, indicating laminar airflow disruption (vorticity) that potentially destabilizes flight and leads to stall.