Somatosensory signaling for flight control

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Hanging bats

    Bats exhibit unequaled flight capabilities, using a variety of completely unique mechanical features and sensory systems. In addition, wing structure and flight behavior differ fundamentally between bats and other flying animals. We are conducting experiments to gain knowledge on the role of somatosensory signals from the wings in flight control in bats that occupy different habitats and engage in different foraging behaviors. For this work, we focus on three species, the insectivorous North American big brown bat, Eptesicus fuscus, the frugivorous tropical bat, Carollia perspicillata, and the tropical nectivorous bat, Glossophaga soricina. Our goal is to better understand dynamic sensorimotor control for target tracking, obstacle avoidance and hovering.

    bat short wing hair

    Somatosensory signals carried from receptors on the batís wing play an important role to the batís flight behavior. As depicted in Figure 1, regular arrays of raised-domes appear along the batís wing membranes, which may carry information about air current and wing position (Zook, Society for Neuroscience meeting abstract, 2005). Each dome contains a central hair with follicular concentrations of Merkel cells, free nerve endings and sebaceous glands, as typically found in mammalian tactile hair receptors. Primary afferent recordings from bat wing receptors have revealed several response types. Domes show predominantly slow-adapting responses to direct contact, and hairs are most sensitive to turbulent airflow. Indeed, the dome hairs may provide feedback on boundary air turbulence necessary for estimations of lift during complex maneuvers. Primary afferent recordings also reveal fast-adapting stretch receptors located near limb joints and at points with elastin bands converge. Wing stretch receptors are highly sensitive to any membrane deformation but relatively insensitive to airflow. Activity in these receptors may provide information to the bat about wing position and stretch. Little research has explored the function of these cutaneous receptors, but evidence suggests that they may play an important role in flight control (Zook, Society for Neuroscience meeting abstract, 2005).

    The wings and tail membrane of the bat are covered with fine hairs, which are believed to carry information about airflow. Surprisingly little research has explored the function of these hairs, but evidence suggests that they may play an important role in flight control. These hairs can be characterized into long or short hairs. Figure 2 illustrates the short hairs, which are thought to aide in flight control.

    bat flight
    Figure 2: Short wing hairs - Scanning electron microscope images from the ventral trailing edge (for location of membrane sample see circles in sketches inserted) of the bat species Eptesicus fuscus (E.f., A) and Carollia perspicillata (C.p., B). C: tip of a tactile wing hair of Eptesicus fuscus, which is only several hundred nanometers in diameter. D: Schematic of the bat wing and its parts. Note the calibration bars on the bottom of each photomicrograph for reference.

    In this project, we aim to determine how flight-driven stimulation of the hairs from selected regions of the batís wing play into the control of flight, particularly for maneuvers that involve rapid adjustments in response to obstacles and for the capture of insect prey. We are conducting neurophysiological and behavioral studies to better understand the functional role of wing hairs in flight control. Neurophysiological experiments emphasize cortical activity in the primary somatosensory cortex of the big brown bat, Eptesicus fuscus. Behavioral studies explore the effects of wing hair removal on flight behaviors in Eptesicus fuscus, Carollia perspicillata and Glossophaga soricina.