Biology

Dr. Sanjay Sane
NCBS Bangalore

Insect flight is elicited and controlled through sensory feedback acquired from multiple sensory modalities. For control in stroke-to-stroke timescales, the role of visual feedback from their compound eyes and mechanosensory feedback from their antennae is thought to be of particular importance. This information is acquired by numerous sensory units on the head, but massively converges by one or two orders of magnitude as it is transmitted via descending neurons in the Ventral Nerve Cord (VNC). This implies that such neurons are capable of filtering, and also perhaps combining the visual and mechanosensory information through descending neurons that multiplex the feedback from multiple sensory modalities. Because this information is required on stroke-to-stroke timescales, it is expected that its transmission occurs via neurons with axons of a large diameter to enhance the conduction velocity. We investigated the presence of such neurons in the VNC in the study system of the Oleander hawk moth, Daphnis nerii which are large and robust fliers. Specifically, we recorded intracellularly from the axons of nearly 90 descending neurons in the VNC, while providing visual and mechanosensory stimuli to their eyes and antennae, respectively. Our recordings show that there exist in the VNC, descending neurons that multiplex the sensory information from visual and antennal mechanosensory units, in addition to others that transmit information from single sensory modalities. To understand the function of these descending neurons, we constructed minimal models of their action such that each model is able to account for all the recorded data for a given neuron. Using these models, we classified these circuits into a smaller subset that respond to specific aspects of their visual and mechanosensory environment. This method allows us to discern rules of multiplexing by these neurons while providing interesting insights into how these circuits might function in the context of active flight. Overall, we expect that such rules can be generalized for most flying insects, but with species-specific adaptations depending on their sensory ecology. In addition to the above multiplexing neurons, I will also describe results from behavioural experiments and anatomical characterization of descending neurons from the primary afferents of the cephalic hair system, which responds to frontal air flow and elicits rapid flight movements in hawk moths.