Descending premotor target tracking systems in flying insects

The control of behaviour in all animals requires efficient transformation of sensory signals into the task-specific activation of muscles. Predation offers an advantageous model behaviour to study the computational organisation underlying sensorimotor control. Predators are optimised through diverse evolutionary arms races to outperform their prey in terms of sensorimotor coordination, leading to highly specialised anatomical adaptations and hunting behaviours, which are often innate and highly stereotyped. Predatory flying insects present an extreme example, performing complex visually-guided pursuits of small, often fast flying prey over extremely small timescales. Furthermore, this behaviour is controlled by a tiny nervous system, leading to pressure on neuronal organisation to be optimised for coding efficiency. In dragonflies, a population of eight pairs of bilaterally symmetric Target Selective Descending Neurons (TSDNs) relay visual information about small moving objects from the brain to the thoracic motor centres. These neurons encode the movement of small moving objects across the dorsal fovea region of the eye which is fixated on prey during predatory pursuit, and are thought to constitute the commands necessary for actuating an interception flight path. TSDNs are characterised by their receptive fields, with responses of each TSDN type spatially confined to a specific portion of the dorsal fovea visual field and tuned to a specific direction of object motion. To date, little is known about the descending representations mediating target tracking in other insects. This dissertation presents a comparative report of descending neurons in a variety of flying insects. The results are organised into three chapters: Chapter 3 identifies TSDNs in demoiselle damselflies and compares their response properties to those previously described in dragonflies. Demoiselle TSDNs are also found to integrate binocular information, which is further elaborated with prism and eyepatch experiments. Chapter 4 describes TSDNs in two dipteran species, the robberfly Holcocephala fusca and the killerfly Coenosia attenuata. Chapter 5 describes an interaction between small- and wide-field visual features in TSDNs of both predatory and nonpredatory dipterans, finding functional similarity of these neurons for prey capture and conspecific pursuit. Dipteran TSDN responses are repressed by background motion in a direction dependent manner, suggesting a control architecture in which target tracking and optomotor stabilization pathways operate in parallel during pursuit.echnology and Biological Sciences ResearchCouncil (BB/M011194/1

Binocular Encoding in the Damselfly Pre-motor Target Tracking System.

Akin to all damselflies, Calopteryx (family Calopterygidae), commonly known as jewel wings or demoiselles, possess dichoptic (separated) eyes with overlapping visual fields of view. In contrast, many dragonfly species possess holoptic (dorsally fused) eyes with limited binocular overlap. We have here compared the neuronal correlates of target tracking between damselfly and dragonfly sister lineages and linked these changes in visual overlap to pre-motor neural adaptations. Although dragonflies attack prey dorsally, we show that demoiselles attack prey frontally. We identify demoiselle target-selective descending neurons (TSDNs) with matching frontal visual receptive fields, anatomically and functionally homologous to the dorsally positioned dragonfly TSDNs. By manipulating visual input using eyepatches and prisms, we show that moving target information at the pre-motor level depends on binocular summation in demoiselles. Consequently, demoiselles encode directional information in a binocularly fused frame of reference such that information of a target moving toward the midline in the left eye is fused with information of the target moving away from the midline in the right eye. This contrasts with dragonfly TSDNs, where receptive fields possess a sharp midline boundary, confining responses to a single visual hemifield in a sagittal frame of reference (i.e., relative to the midline). Our results indicate that, although TSDNs are conserved across Odonata, their neural inputs, and thus the upstream organization of the target tracking system, differ significantly and match divergence in eye design and predatory strategies. VIDEO ABSTRACT

Reactor physics project progress report

Statement of responsibility on title page reads: Editors: M.J. Driscoll and T.J. Thompson; Contributors: F.M. Clikeman, J.N. Donohew, M.J. Driscoll, J.D. Eckard, T.L. Harper, Y. Hukai, I. Kaplan, C.H. Kim, Y.-M. Lefevre, T.C. Leung, N.R. Ortiz, N.C. Rasmussen, C.S. Rim, S.S. Seth, A.T. Supple C. Takahata, and T.J. Thompson"MIT-3944-1."Progress report; September 30, 1968U.S. Atomic Energy Commission contract AT(30-1)-394

Reactor physics project progress report no. 2

Statement of responsibility on title page reads: Editors: M.J. Driscoll, I. Kaplan, D.D. Lanning; Contributors: V. Agarwala, F.M. Clikeman, J.N. Donohew, M.J. Driscoll, G. T. Hamilton, T.L. Harper, Y. Hukai, I. Kaplan, T. J. Kelley, D.D. Lanning, T.C. Leung, E.L. McFarland, N.C. Rasmussen, S.S. Seth, J.M. Sicilian, G.E. Sullivan, A.T.Supple and T.J. Thompson"September 30, 1969.""MIT-3944-4."Includes bibliographical referencesProgress report no. 2; October 1, 1968 through September 30. 1969This is the second annual report in an experimental and theoretical program to develop and apply single and few element heterogeneous methods for the determination of reactor lattice parameters. During the period covered by the report, October 1, 1968 through September 30. 1969, work was primarily devoted to measurement of the heterogeneous fuel element parameters (F, rl and A) of 19- and 31- rod clusters of plutonium-containing fuel. Methods development research focused on determination of the epithermal absorption constant, A. Calculations and an analysis of data reported in the literature were made to assess the applicability of heterogeneous methods to H 20- moderated systems. Advanced gamma spectrometric methods using Ge(Li) detectors were applied to the analysis of prompt and delayed gamma spectra from fertile and fissile materials and from fuel elements. These methods were used successfully for nondestructive analysis of the composition of fuel elements. A feasibility study was performed on an in-pile gamma spectrometer. Two fuel pins irradiated to a burnup of approximately 20,000 MWD/MT in the Dresden reactor were received and preparations made for their analysis and use in reactor physics experiments.U. S. Atomic Energy Commission contract AT(30-1)-394

Integration of Small- and Wide-Field Visual Features in Target-Selective Descending Neurons of both Predatory and Non-Predatory Dipterans

For many animals, target motion carries high ecological significance as this may be generated by a predator, prey or potential mate. Indeed, animals whose survival depends on early target detection are often equipped with a sharply tuned visual system, yielding robust performance in challenging conditions. For example, many fast-flying insects use visual cues for identifying targets, such as prey (e.g. predatory dragonflies and robberflies) or conspecifics (e.g. non-predatory hoverflies), and can often do so against self-generated background optic flow. Supporting these behaviors, the optic lobes of insects that pursue targets harbor neurons that respond robustly to the motion of small moving objects, even when displayed against syn-directional background clutter. However, in diptera, the encoding of target information by the descending neurons, which are more directly involved in generating the behavioral output, has received less attention. We characterized target selective neurons by recording in the ventral nerve cord of male and female predatory Holcocephala fusca robberflies and of male non-predatory Eristalis tenax hoverflies. We show that both species have dipteran target-selective descending neurons (dTSDNs) that only respond to target motion if the background is stationary or moving slowly, moves in the opposite direction, or has un-naturalistic spatial characteristics. The response to the target is suppressed when background and target move at similar velocities, which is strikingly different to the response of target neurons in the optic lobes. As the neurons we recorded from are pre-motor, our findings affect our interpretation of the neurophysiology underlying target-tracking behaviors.SIGNIFICANCE STATEMENTMany animals use sensory cues to detect moving targets that may represent predators, prey or conspecifics. For example, birds of prey show superb sensitivity to the motion of small prey, and intercept these at high speeds. In a similar manner, predatory insects visually track moving prey, often against cluttered backgrounds. Accompanying this behavior, the brains of insects that pursue targets contain neurons that respond exclusively to target motion. We here show that dipteran insects also have target selective descending neurons in the part of their nervous system that corresponds to the vertebrate spinal cord. Surprisingly, and in contrast to the neurons in the brain, these pre-motor neurons are inhibited by background patterns moving in the same direction as the target.P.T.G.-B. and K.N. contributed equally to this work.</p

Activation of P2X4 receptors induces an increase in the area of the extracellular region and a decrease in receptor mobility.

The P2X4 receptor (P2X4R) is an ATP-gated cation channel. Here, we used fast-scan atomic force microscopy (AFM) to visualize changes in the structure and mobility of individual P2X4Rs in response to activation. P2X4Rs were purified from detergent extracts of transfected cells and integrated into lipid bilayers. Activation resulted in a rapid (2 s) and substantial (10-20 nm2 ) increase in the cross-sectional area of the extracellular region of the receptor and a corresponding decrease in receptor mobility. Both effects were blocked by the P2X4R antagonist 5-BDBD. Addition of cholesterol to the bilayer reduced receptor mobility, although the ATP-induced reduction in mobility was still observed. We suggest that the observed responses to activation may have functional consequences for purinergic signalling