Comparative Analysis of RF-Transmitted Neural Activity Underlying Visual Flight Control in Insect

Acronym: 
NAA-u-VLC
Research Areas: 
A
Abstract: 

In this international cooperation project we try to overcome current technical constrains and aim to record neuronal signals in the brain of freely moving insects. The results will provide the opportunity to study how the nervous system implements control strategies for head stabilization and collision avoidance based on complex time-varying visual and mechanosensory inputs. As a first step, we investigate compensatory head movements of blowflies which are walking freely on differently structured substrates.

 

Methods and Research Questions: 

The neural basis of insect walking behavior provides a unique opportunity to study control strategies for eye and body stabilization based on visual and mechanosensory inputs. We approach this control system by tracking head and body movements of freely walking blowflies while recording their brain activity with autonomous neural recoding probes.

The neural basis of insect flight and walking behavior provides a unique opportunity to study control strategies for eye and body stabilization as well as mechanisms of collision avoidance based on visual and mechanosensory inputs. Up to now, it has proven impossible to record neural activity from the brain of freely moving insects. To overcome this technical challenge we combine the expertise of four different laboratories. The part of our lab in this cooperation will be the establishment of an automatic and precise head tracking method. Head tracking is essential to reconstruct the visual stimuli perceived by a freely walking insect. Thereafter, we will be able to record the brain activity of freely walking blowflies and correlate it with the previously reconstructed visual stimuli. For the electrophysiological recordings we will use an autonomous neural recording probe developed by our cooperation partners. As a first step to reach this goal, we have developed a high-speed video tracking method to analyze the head and body position as well as the orientation of freely walking blowflies. To combine this methodological development with an interesting biological question, we have analyzed the head and thereby eye stabilization behavior of blowflies walking on differently structured substrates.

We used two synchronized high-speed cameras to record blowflies walking on differently structured substrates. The tested flies (average body length 9 mm) are prevented from flying. Five points on the fly’s head and thorax were marked with white, non-toxic acrylic paint. These marker points were automatically tracked by the in-house made tracking software: “ivTrace” (available at: http://opensource.cit-ec.de/projects/ivtools). The image pixel coordinates of the tracked markers were then used to stereo triangulate the position of the head and body in space. The tracking acuity in space was 0.03 mm. Subsequently, the marker positions can be used to calculate the orientation angle of the flies’ head and the body with an error of 1°. We recorded ten flies, each walking three times over four differently structured substrates (regularly placed hemispheres; Ø: 3 mm, 6 mm and 8 mm). The control condition was a flat substrate (called 0 mm) to determine head and body movements caused exclusively by the walking apparatus. In addition, we estimated the influence of the visual system for the control of gaze stabilization during walking on structured substrates. Therefore, we recorded fly walks in the dark under infra-red illumination which is unperceivable by the fly.

 

Outcomes: 

We found that body as well as head and, thus, gaze orientation of freely walking blowflies are effectively stabilized, with residual rotational fluctuations ranging between 2° - 5° around all axes.
Surprisingly, even on coarsely structured ground with surface bumps in the size of the animal, gaze stability is only marginally reduced for pitch and yaw and held relatively constant for roll.
For all tested surface conditions head movements compensate 25% of the angle of the remaining fluctuations of body pitch and 46% of the angle of the remaining body roll fluctuations. Head and body rotations of walking blowflies were found to be coupled, to some extent, to the step cycle. This coupling is less prominent on strongly structured substrates. Rotational head stability stays consistently good in the dark.

Therefore, we conclude that head and, thus, gaze stability in blowflies walking on structured substrates is not controlled visually but essentially by mechanosensory systems.