Wide-field Patterns Research Articles

Full-field time-resolved fluorescence tomography of small animals

In this experimental investigation, we explore the feasibility of using wide-field illumination for time-resolved fluorescence molecular tomography. The performance of wide-field patterns with a time-resolved imaging platform is investigated in vitro and in a small animal model. A Monte Carlo-based forward model is employed to reconstruct fluorescence yield based on time-gated datasets. An improvement in resolution and quantification when using the time-gate data type compared to the commonly used cw data type is demonstrated in vitro. Furthermore, the feasibility of wide-field strategies for fluorescence preclinical applications is established by an accurate localization of a fluorescent inclusion implanted in the chest cavity of a murine model.

Mutation of theDrosophilavesicular GABA transporter disrupts visual figure detection

The role of gamma amino butyric acid (GABA) release and inhibitory neurotransmission in regulating most behaviors remains unclear. The vesicular GABA transporter (VGAT) is required for the storage of GABA in synaptic vesicles and provides a potentially useful probe for inhibitory circuits. However, specific pharmacologic agents for VGAT are not available, and VGAT knockout mice are embryonically lethal, thus precluding behavioral studies. We have identified the Drosophila ortholog of the vesicular GABA transporter gene (which we refer to as dVGAT), immunocytologically mapped dVGAT protein expression in the larva and adult and characterized a dVGAT(minos) mutant allele. dVGAT is embryonically lethal and we do not detect residual dVGAT expression, suggesting that it is either a strong hypomorph or a null. To investigate the function of VGAT and GABA signaling in adult visual flight behavior, we have selectively rescued the dVGAT mutant during development. We show that reduced GABA release does not compromise the active optomotor control of wide-field pattern motion. Conversely, reduced dVGAT expression disrupts normal object tracking and figure-ground discrimination. These results demonstrate that visual behaviors are segregated by the level of GABA signaling in flies, and more generally establish dVGAT as a model to study the contribution of GABA release to other complex behaviors.

Bioinspired Visuomotor Convergence

In this paper, wide-field integration methods, which are inspired by the spatial decompositions of wide-field patterns of optic flow in the insect visuomotor system, are explored as an efficient means to extract visual cues for guidance and navigation. A control-theoretic framework is developed and used to quantitatively link weighting functions to behaviorally-relevant interpretations such as relative orientation, position, and speed in a corridor environment. It is shown through analysis and demonstration on a ground vehicle that the proposed sensorimotor architecture gives rise to navigational heuristics, namely, centering and speed regulation, which are observed in natural systems.

A biologically inspired modular VLSI system for visual measurement of self-motion

We introduce a biologically inspired computational architecture for small-field detection and wide-field spatial integration of visual motion based on the general organizing principles of visual motion processing common to organisms from insects to primates. This highly parallel architecture begins with two-dimensional (2-D) image transduction and signal conditioning, performs small-field motion detection with a number of parallel motion arrays, and then spatially integrates the small-field motion units to synthesize units sensitive to complex wide-field patterns of visual motion. We present a theoretical analysis demonstrating the architecture's potential in discrimination of wide-field motion patterns such as those which might be generated by self-motion. A custom VLSI hardware implementation of this architecture is also described, incorporating both analog and digital circuitry. The individual custom VLSI elements are analyzed and characterized, and system-level test results demonstrate the ability of the system to selectively respond to certain motion patterns, such as those that might be encountered in self-motion, at the exclusion of others.

Pheromone-modulated optomotor response in male gypsy moths, Lymantria dispar L.: Directionally selective visual interneurons in the ventral nerve cord

In response female pheromone the male gypsy moth flies a zigzagging path upwind to locate the source of odor. He determines wind direction visually. To learn more about the mechanism underlying this behavior, we studied descending interneurons with dye-filled micro-electrodes. We studied the interneuronal responses to combinations of pheromone and visual stimuli. 1. We recorded 5 neurons whose directionally selective visual responses to wide field pattern movement were amplified by pheromone (Figs. 2–6). 2. The activity of the above neurons was more closely correlated with the position of the moving pattern than with its velocity (Fig. 4). 3. One neuron showed no clearly directional visual response and no response to pheromone. Yet in the presence of pheromone it showed directionally selective visual responses (Fig. 6). 4. We recorded 4 neurons whose directionally selective visual responses were not modulated by pheromone (Fig. 7), ruling out the possibility that the effect of the pheromone was simply to raise the activity of all visual neurons. 5. Our results suggest that female pheromone amplifies some neural pathways mediating male optomotor responses, especially the directionally selective responses to the transverse movement of the image, both below and above the animal.

Visual processing of moving single objects and wide-field patterns in flies: Behavioural analysis after laser-surgical removal of interneurons

A laser micro-beam unit was used to reproducibly and selectively eliminate the large horizontal and vertical motion sensitive neurons (H- and V-cells) of the lobula plate on one side of the brain of house fliesMusca domestica. This was achieved by ablating the precursors of these cells deep in the larval brain without damaging other cells in the brain or other tissues. The individually reared flies were tested for their behaviour. Three tests were performed: (i) visual fixation of a single stripe, (ii) the optomotor turning and thrust response to a stripe moving clockwise and counterclockwise around the fly, (iii) the monocular turning response to a moving grating. The responses to a moving single object were normal on both sides, the control side and the one lacking the H- and V-cells. However, the responses to a moving grating were reduced on the side lacking H- and V-cells for progressive (front to back) and regressive (back to front) motion. From this we conclude that the response to single objects is controlled mainly by cells other than the H- and V-cells. We also suggest two separate pathways for the processing of single object motion and wide field pattern motion respectively (Fig. 8). Furthermore, the H- and V-cells might function as visual stabilizers and background motion processors.

Patterns and fields of dorsal column fiber terminals in the cuneo-gracile nuclei of the rat

The organization of the patterns and fields generated by dorsal column fibers terminating in the dorsal column nuclei was studied in Golgi preparations. Five main categories of dorsal column fiber terminal patterns were noted: (a) Numerous collaterals generated as microbundles from dorsal column stem axons stream ventrally into the nuclei. These microbundles later develop secondary and tertiary branchings in a moderately replicative, wide-field pattern, with considerable overlap between the terminal fields of adjoining microbundles. (b) Other collaterals take a dorsal course and terminate in the form of small, discrete, flame-shaped arbors. Both ventrally and dorsally directed dorsal column collaterals frequently end on dendritic agglomerations or dendritic nests formed by dendrites of certain neurons of the nuclei. (c) Some dorsal column stem axons project directly into the nuclei. These may also generate discrete or wide-field terminals. (d) Another category of terminal fiber pattern is generated by border fibers which end with a transverse spread on neurons situated superficially in the nuclei. (e) The last category is represented by running fiber terminal patterns. The fibers with such terminal endings presumably originate from the dorsal column, singly or in small groups, and run ventrally into the cuneo-gracile nuclei with very little secondary or tertiary branchings. I suggest that these different terminal patterns may represent structural expressions of functional relevance to receptive field determination and modality representation in the cuneo-gracile nuclei.