Responses of a Looming-Sensitive Neuron to Compound and Paired Object Approaches

Abstract

Guest, Bruce B. and John R. Gray. Responses of a looming sensitive neuron to compound and paired object approaches. J Neurophysiol 95: 1428 -1441, 2006. First published November 30, 2005 doi:10.1152/jn.01037.2005. The lobula giant movement detector (LGMD) and its target neuron, the descending contralateral movement detector (DCMD), constitute a motion-sensitive pathway in the locust visual system that responds preferentially to objects approaching on a collision course.LGMD receptive field properties, anisotropic distribution of local retinotopic inputs across the visual field, and localized habituation to repeated stimuli suggest that this pathway should be sensitive to approaches of individual objects within a complex visual scene. We presented locusts with compound looming objects while recording from the DCMD to test the effects of nonuniform edge expansion on looming responses. We also presented paired objects approaching from different regions of the visual field at nonoverlapping, closely timed and simultaneous approach intervals to study DCMD responses to multiple looming stimuli. We found that looming compound objects evoked characteristic responses in the DCMD and that the time of peak firing was consistent with predicted values based on a weighted ratio of the half size of each distinct object edge and the absolute approach velocity. We also found that the azimuthal position and interval of paired approaches affected DCMD firing properties and that DCMDs responded to individual objects approaching within 106 ms of each other. Moreover, comparisons between individual and paired approaches revealed that overlapping approaches are processed in a strongly sublinear manner. These findings are consistent with biophysical mechanisms that produce nonlinear integration of excitatory and feed-forward inhibitory inputs onto the LGMD that have been shown to underlie responses to looming stimuli.

Background visual motion affects responses of an insect motion-sensitive neuron to objects deviating from a collision course

“…We used a 1.2 msec TTL pulse included in each video frame along with the Vsync pulse from the video card (NVIDIA GeForce 7900 GTX 512 MB) to align neuronal recordings with visual stimuli. The Michelson contrast ratio (0.49) and luminance values were similar to those used in previous studies (Guest and Gray ; McMillan and Gray ; Dick and Gray ; Silva et al. ).…”

Relationship between the Phases of Sensory and Motor Activity during a Looming-Evoked Multistage Escape Behavior

“…Estimates of the instantaneous DCMD firing rate show that its peak occurs closer to collision at l/͉v͉ ϭ 40 than 120 ms. Indeed, over the range of l/͉v͉ values previously tested, l/͉v͉ ϭ 5-50 ms, the time of the DCMD peak firing rate always occurred closer to collision as l/͉v͉ decreased and was a linear function of l/͉v͉ (Gabbiani et al, 1999;Matheson et al, 2004;Guest and Gray, 2006). We also observed a high positive correlation between l/͉v͉ and the timing of the DCMD peak over the 40 -120 ms range ( ϭ 0.8; n ϭ 7 animals, ES1).…”

“…Thus, the LGMD and DCMD have been long thought to be involved in the generation of fast escape behaviors. The responses of the LGMD/DCMD to approaching objects have been studied in detail (Judge and Rind, 1997;Gabbiani et al, 1999Gabbiani et al, , 2001Matheson et al, 2004;Guest and Gray, 2006). During approach on a collision course, the firing rate increases, peaks, and then decays near the end of approach.…”

A sublethal dose of a neonicotinoid insecticide disrupts visual processing and collision avoidance behaviour in Locusta migratoria

“…Electrophysiological experiments were conducted with animals mounted in a flight simulator with a rear-projection dome, as described in Guest and Gray 71 . The stimulus was the image of a 7 cm black disk traveling at 300 cm/s, created with Vision Egg visual stimulus generation software 69 on a Python programming platform and represented as a 1,024 × 1,024 pixel portable network graphics (png) file.…”