Neural responses of hoverfly Target Selective Descending Neurons to reconstructed target pursuits

Many animals use motion vision information to control dynamic behaviours. Male hoverflies (Eristalis tenax) guard their territory against intruders using visual cues, followed by high-speed pursuit. It is believed that target pursuit is subserved by specialised target-tuned neurons found in the lobula complex. These neurons likely synapse with Target Selective Descending Neurons (TSDNs), which provide input to the motor command centres in the thoracic ganglion. However, it remains unclear how TSDNs respond during pursuits.

To address this, we reconstructed visual flow-fields as experienced by hoverflies during actual pursuits of artificial targets (black beads). We used behavioural pursuits filmed with two high speed cameras, followed by 3D reconstructions of the hoverfly and the target trajectory over time. We then took these 3D reconstructions, calculated the retinal image of the target at each point in time, followed by the perspective corrected 2D representation of the retinal image to show on a monitor for electrophysiology. We found that the size of the target image as seen during pursuits tended to peak at 1.2 degrees, and that the target image moved at high retinal velocities, peaking at 570 deg/s. Furthermore, we found that the target image could move in all directions, but that horizontal motion was more prevalent.

We identified the location of TSDN receptive fields, each neuron’s preferred direction, size and speed tuning. We found that TSDNs (N=109) have receptive fields in the dorso-frontal visual field, with a preferred direction up and away from the visual midline. We also found that the TSDN response increases with target velocity, up to 300 deg/s. The strongest response was found to 10 deg targets. We next recorded extracellular electrophysiological responses to 6 reconstructed pursuits in 13 TSDNs. We found that a high response probability coincided with the location of the TSDN receptive field and with the neuron’s preferred direction.

Short Bio

Yuri Ogawa was awarded her PhD in Biological Sciences in 2013 from The Graduate University for Advanced Studies (SOKENDAI), Japan. During her PhD study she demonstrated the physiological basis of butterfly colour vision, supervised by Professor Kentaro Arikawa. After finishing her PhD, Yuri came to Australia, where she did her first post doctoral training with Associate Professor Jan M Hemmi at The University of Western Australia.

She worked on the colour vision in both nocturnal and diurnal Australian bull ants and the visual system in fiddler crabs. In 2016 she moved to Macquarie University in Sydney to join Dr Ajay Narendra’s lab to study visual navigation and eyes in Australian bull ants. Yuri joined the Insect Vision group at Flinders University in 2019, where she is currently working with Professor Karin Nordström to investigate the mechanisms underlying small target detection in hoverflies. The focus of Yuri’s career has been to understand how animals optimally sense visual information and how the visual capacities of different species have been shaped by natural selection. The manner by which animals sense their environment has much to teach us about visual communication.

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