Spike Burst Coding of Translatory Optic Flow and Depth from Motion in the Fly Visual System

Abstract

Many animals use the visual motion generated by traveling straight-the translatory optic flow-to successfully navigate obstacles: near objects appear larger and to move more quickly than distant objects. Flies are expert at navigating cluttered environments, and while their visual processing of rotatory optic flow is understood in exquisite detail, how they process translatory optic flow remains a mystery. We present novel cell types that have local motion receptive fields matched to translation self-motion, the vertical translation (VT) cells. One of these, the VT1 cell, encodes self-motion in the forward-sideslip direction and fires action potentials in spike bursts as well as single spikes. We show that the spike burst coding is size and speed-tuned and is selectively modulated by motion parallax-the relative motion experienced during translation. These properties are spatially organized, so that the cell is most excited by clutter rather than isolated objects. When the fly is presented with a simulation of flying past an elevated object, the spike burst activity is modulated by the height of the object, and the rate of single spikes is unaffected. When the moving object alone is experienced, the cell is weakly driven. Meanwhile, the VT2-3 cells have motion receptive fields matched to the lift axis. In conjunction with previously described horizontal cells, the VT cells have properties well suited to the visual navigation of clutter and to encode the fly's movements along near cardinal axes of thrust, lift, and forward sideslip.

Optomotor steering and flight control requires a specific sub-section of the compound eye in the hawkmoth,Manduca sexta

“…Their conclusions confirmed a prediction by Krapp and Hengstenberg (1996) that rotational and translational optic flow detection may be different information streams. This hypothesis is supported by the discovery of a neural correlate in that visual interneuron VT1 fires spike bursts when presented with translational cues (Longden et al, 2017). It would be interesting to perform a set of experiments similar to those of Mazo and Theobald (2014) to see whether this model holds true for moths.…”

M current regulates firing mode and spike reliability in a collision-detecting neuron

“…By multiplexing tonic and burst spiking, neurons increase their ability to both detect and discriminate, or to encode sensory information with both sensitivity and selectivity (Krahe and Gabbiani 2004;Sherman 2001). The use of burst and nonburst spiking as distinct firing modes has been demonstrated in contexts as diverse as audition in crickets, vision in flies, the electrosensory system of weakly electric fish, and the mammalian lateral geniculate nucleus of the thalamus (Allen and Marsat 2018;Clarke et al 2015;Lesica and Stanley 2004;Longden et al 2017;Marsat and Pollack 2006). In these systems, changes in a neuron's firing mode signify a change between detection and discrimination.…”

Multielectrode Recordings From Identified Neurons Involved in Visually Elicited Escape Behavior

“…On the other hand, the raster plot of Figure 3H shows a spontaneous activity made of bursts. We then analyzed the firing pattern of all our MLG2 and BLG2 classified units, by calculating the percentage of total spikes that occurred as bursts of three or more spikes with an interspike interval of less than 15 ms (Longden et al, 2017 ). The mean ± SEM percentage for the MLG2 units ( n = 5) was 3.3 ± 1, 4 and for the BLG2 units ( n = 8) was 15.7 ± 2.7, a difference that was statistically significant ( p < 0.01, Student’s t -test).…”