Visual neuroscience: how flies segregate moving objects from the optic flow field

Moving animals often have difficulty detecting moving objects because self-generated optic flow patterns confound image motion. The new hypothesis of 'regressive motion salience' reveals simple rules used by fruit?flies.     

Response patterns of two auditory interneurons in a freely moving grasshopper (Chorthippus biguttulus L.)

Summary Summated nerve potentials were recorded from the neck connectives in intact, freely moving grasshoppers of the speciesChorthippus biguttulus by means of chronically implanted hook electrodes. The action potentials of two auditory interneurons, known as the G₁- and the B₁-neuron, respectively (Kalmring 1975a, b), were distinguishable (Fig. 1) in the recordings and the neurons were identified by their morphology (Fig. 2).The G-neuron exhibits a very rapid and another, much slower, response decrement; the times required for recovery from both these effects show the opposite time courses (Fig. 3). The response versus intensity curve of the G-neuron has the shape of a saturating characteristic for noise stimuli and high frequencies whereas at low frequencies inhibitory effects can be observed for high intensities. The B-neuron has a bell-shaped intensity characteristic at all frequencies with position and width of the bell being frequency-dependent (Fig. 5). The directional characteristic of the G-neuron is nearly circular (for noise stimuli); the B-neuron responds preferentially to sound from the ipsilateral side (Fig. 6). With increasing temperature the threshold, latency, and spike interval of the G-neuron strongly decrease, while the number of spikes per stimulus increases (Fig. 7).In general, the response properties of both auditory interneurons as determined in almost intactChorthippus biguttulus, largely resemble those previously reported forLocusta migratoria in extensively dissected preparations. However, a few, probably interspecific, differences were observed.     

A fine analysis of glucose-phosphate-isomerase patterns in single preimplantation mouse embryos

Mouse embryos were derived from eggs heterozygous for alleles of the dimeric enzyme glucose phosphate isomerase (Gpi-1a/Gpi-1b) that had been fertilized with sperm carrying a third allele (Gpi-1c). This particular combination makes it possible to study the activity of the paternally derived as well as the maternally derived genes, the persistence of oocyte-coded enzyme throughout early development and the possible simultaneous expression of both the paternally derived allele and the maternal message. The different isozymes present in single embryos were separated by electrophoresis. The results show that the oocyte-coded glucose phosphate isomerase is gradually replaced by embryo-coded enzyme. Expression of the paternally derived allele was first detected at the morula stage, during which the translation of the maternally derived message seemed to be either exhausted or below the detection limit of our system. Some oocyte-coded enzyme persisted until after implantation.     

Visual memory of shapes in quail chicks: discrimination among 2-dimensional objects

Newly hatched chicks spontaneously peck at conspicuous objects, and soon learn to discriminate between edible food particles and inedible objects. To examine whether this discrimination is based on a chick's ability to memorize objects by shape cues, we analyzed the pecking behavior. One- to 3-day old quail chicks (Coturnix japonica) were presented with dry objects of different shapes (ball, disk, triangle and T-shape) of similar size (4 mm) and color (green). Habituation occurred after repeated presentation of any one of these objects (duration: 30 sec; interval: 4 min). When chicks showed significantly more pecks at a novel object (dishabituation), we assumed that chicks had memorized the habituated shapes and distinguished the novel object. Chicks did not show dishabituation between a ball and a disk. On the other hand, chicks discriminated a triangle or T-shape from the memorized image of disk, but did not memorize either triangle or T-shape by its shape. Similarly, chicks did not memorize the size of disks as a reference for subsequent pecking behavior. Chicks proved to have a limited ability to memorize shape and size cues for selective pecking behavior, in strong contrast to their accurate memorization of colors.     

Two types of information processing in cercal systems of insects: directional sensitivity of giant interneurons

Summary Cercal systems of seven insect species (cricketMelanogryllus desertus, mole cricketGryllotalpa gryllotalpa, katydidsPholidoptera pustulipes andTettigonia viridissima, cockroachesPeriplaneta americana andBlatta orientalis, and locustLocusta migratoria) were examined for direction-sensitive giant interneurons (GIs) that are excited by cercal receptors but have directional preferences independent of cercus position. Such GIs are known for the cricketsAcheta domesticus andGryllus bimaculatus. Directional sensitivity diagrams (DSDs) of GIs were obtained by recording and analysing the electrical responses of abdominal connectives to sound stimuli from various directions. For each animal DSDs were plotted in the form of polar graphs for two or three positions of the stimulated cercus so that the effect of cercus position on the orientation of the DSD could be evaluated.All insects studied had GIs whose DSDs for fixed cercus positions were similar in appearance to the DSDs described for GIs of the cricketsAcheta domesticus andGryllus bimaculatus. Most of these DSDs were shaped like a figure 8 (when airflow is used as the stimulus instead of sound, each DSD has only one lobe). However, not all GIs demonstrated a constant directional preference. GIs with constant directionality were found only inMelanogryllus desertus, Pholidoptera pustulipes, Tettigonia viridissima andLocusta migratoria. In these insects DSDs from one GI plotted for different cercus positions had approximately the same orientation (Figs. 4–7). In contrast, GIs inGryllotalpa gryllotalpa, Periplaneta americana andBlatta orientalis had DSDs whose orientation changed in accordance with a change in position of the stimulated cercus (Figs. 8–10).Thus, direction-sensitive GIs investigated here can be divided into two types: (1) GIs with constant directionality (whose DSDs are fixed to the body, and (2) GIs with variable directionality (whose DSDs are fixed to the cerci). To date, in each species only GIs of the same type have been encountered. This may be an indication that cercal systems can be divided into two categories according to how they process information. However, since we have not tested all GIs in each species, we cannot rule out the possibility that a species might have both types of GIs.Abbreviations DSD directional sensitivity diagram - GI giant interneuron - TAG terminal abdominal ganglion     

Visual position stabilization in the hummingbird hawk moth, Macroglossum stellatarum L. II. Electrophysiological analysis of neurons sensitive to wide-field image motion

Response properties of neurons in the cervical connectives of the hummingbird hawk moth, Macroglossum stellatarum L., were determined. All neurons described in this account respond directionally selectively to motion in large parts of the visual field of either eye. They respond maximally to bilateral stimulation, preferring either motion as induced on the eyes during translatory movements of the animal or when it turns around one of its body axes. Cells most sensitive to rotational motion either respond best to rotation of the patterns around the vertical axis of the animal or around its longitudinal body axis. Neurons most sensitive to translational pattern motion respond best to either simulated translations of the animal along its vertical or along an oblique axis. Most types of neurons respond tonically and do not habituate. The sensitivity to motion stimuli is not evenly distributed within the receptive field of any investigated neuron. Part of these neurons might play a role in visual position and course stabilization. Accepted: 13 August 1997     

Spatial and temporal patterns of cell death in limb bud mesoderm after apical ectodermal ridge removal

A spatiotemporal pattern of cell death occurred in the chick wing and leg bud mesoderm after removal of apical ectodermal ridge at stages 18–20. Cells died in a region extending from the limb bud distal surface to 150–200 μm into the mesoderm. Limb buds from which ridge was removed at later stages in development did not exhibit a spatiotemporal pattern of cell death. In control experiments in which dorsal ectoderm was removed, a pattern of cell death did not occur. Removal of the ridge and part of the 150- to 200-μm zone of prospective cell death resulted in cell death in an area approximately equal to the amount of the zone remaining. After removal of all of the prospective zone of cell death plus the apical ridge, cell death was observed in the remaining limb bud mesoderm. In these limb buds, cell death occurred in a region in which it had not been seen in limb bud with apical ridge alone removed. We conclude that at stages 18–20 the mesodermal cells 150–200 μm beneath the ridge require the apical ridge to survive. More proximal mesodermal cells do not die after ridge removal alone, but apparently require the presence of the more distal mesoderm to survive. Whether this is a requirement for something intrinsic to the distal mesoderm or something it possesses by way of the ridge is unknown. After stage 23, the limb mesoderm cells do not die when the apical ridge is removed. Nevertheless, at the later stages, ridge continues to be required for limb bud proximal-distal elongation and the differentiation of distal limb elements.     

Local interneurons and information processing in the olfactory glomeruli of the moth Manduca sexta

Intracellular recordings were made from the major neurites of local interneurons in the moth antennal lobe. Antennal nerve stimulation evoked 3 patterns of postsynaptic activity: (i) a short-latency compound excitatory postsynaptic potential that, based on electrical stimulation of the antennal nerve and stimulation of the antenna with odors, represents a monosynaptic input from olfactory afferent axons (71 out of 86 neurons), (ii) a delayed activation of firing in response to both electrical- and odor-driven input (11 neurons), and (iii) a delayed membrane hyperpolarization in response to antennal nerve input (4 neurons).Simultaneous intracellular recordings from a local interneuron with short-latency responses and a projection (output) neuron revealed unidirectional synaptic interactions between these two cell types. In 20% of the 30 pairs studied, spontaneous and current-induced spiking activity in a local interneuron correlated with hyperpolarization and suppression of firing in a projection neuron. No evidence for recurrent or feedback inhibition of projection neurons was found. Furthermore, suppression of firing in an inhibitory local interneuron led to an increase in firing in the normally quiescent projection neuron, suggesting that a disinhibitory pathway may mediate excitation in projection neurons. This is the first direct evidence of an inhibitory role for local interneurons in olfactory information processing in insects. Through different types of multisynaptic interactions with projection neurons, local interneurons help to generate and shape the output from olfactory glomeruli in the antennal lobe.Abbreviations AL antennal lobe - EPSP excitatory postsynaptic potential - GABA -aminobutyric acid - IPSP inhibitory postsynaptic potential - LN local interneuron - MGC macroglomerular complex - OB olfactory bulb - PN projection neuron - TES N-tris[hydroxymethyl]methyl-2-aminoethane-sulfonic acid     

Genetic analysis of nicotinic signaling in worms and flies

The nicotinic acetylcholine receptor is among the most thoroughly characterized molecules in the nervous system, and its role in mediating fast cholinergic neurotransmission has been broadly conserved in both vertebrates and invertebrates. However, the accessory molecules that facilitate or regulate nicotinic signaling remain mostly unknown. One approach to identify such molecules is to use molecular genetics in a simple, experimentally accessible organism to identify genes required for nicotinic signaling and to determine the molecular identity of the mutant genes through molecular cloning. Because cellular signaling pathways are often highly conserved between different animal phyla, the information gained from studies of simple organisms has historically provided many critical insights into more complex organisms, including humans. Genetic screens essentially make no prior assumptions about the types of molecules involved in the process being studied; thus, they are well suited for identifying previously unknown components of cell signaling pathways. The sophisticated genetic tools available in organisms such as the nematode Caenorhabditis elegans and the fruit fly Drosophila melanogaster have also proven extremely powerful in elucidating complex biologic pathways in the absence of prior biochemical information and for assessing a molecule's in vivo function of in the context of an intact nervous system. This review describes how genetic analysis has been used to investigate nicotinic signaling mechanisms in worms and flies, and the prospects for using these studies to gain insight into nicotinic receptor function and regulation in humans.     

Information processing by nonspiking interneurons: passive and active properties of dendritic membrane determine synaptic integration

Nonspiking interneurons control activities of postsynaptic cells without generating action potentials in the central nervous system of many invertebrates. Physiological characteristics of their dendritic membrane have been analyzed in previous studies using single electrode current- and voltage-clamp techniques. We constructed a single compartment model of an identified nonspiking interneuron of crayfish. Experimental results allowed us to simulate how the passive and active properties of the dendritic membrane influence the integrative processing of synaptic inputs. The results showed that not only the peak amplitude but also the time course of synaptic potentials were dependent on the membrane potential level at which the synaptic activity was evoked. When the synaptic input came sequentially, each individual input was still discernible at depolarized levels at which the membrane time constant was short due to depolarization-dependent membrane conductances. In contrast, synaptic potentials merged with each other to develop a sustained potential at hyperpolarized levels where the membrane behaved passively. Thus, synaptic integration in a single nonspiking interneuron depends on the value of membrane potential at which it occurs. This probably reflects the temporal resolution required for specific types of information processing.     

Visual priming and perception of small pictures in a scene with multiscale objects

Biederman et al. [1, 2] have shown that the priming effect does not depend on the difference between the angular sizes of the test stimulus and the primer. However, these two and other similar studies investigated only a small range of the angular sizes of stimuli. Vakhrameeva et al. [3] have shown that there exist two perceptionally different size ranges: perception of the objects with an angular size varying between 1–1.5 and 50 degrees was found to be invariant, but for the objects whose angular size is less than 1–1.5 degrees, their perception is no longer invariant. In this study, the presence of the priming effect has been investigated in the match-to-sample task with such a difference in the angular sizes of the primer and test stimuli that the sizes of the primer (about 4 degrees) and the test stimulus (about 0.5 degrees) belonged to two different size ranges. The sample stimulus was presented with and without noise superposition. It has been shown that the priming effect is suppressed when the size difference between the primer and the test stimulus is large. A congruent primer can have a positive impact on the recognition of the test objects, but this occurs under the viewing conditions complicated by noise superposition.     

Prey processing in amniotes: biomechanical and behavioral patterns of food reduction

In this paper we examine the biomechanics of prey processing behavior in the amniotes. Whether amniotes swallow prey items whole or swallow highly processed slurries or boluses of food, they share a common biomechanical system where hard surfaces (teeth or beaks) are brought together on articulated jaws by the actions of adductor muscles to grasp and process food. How have amniotes modified this basic system to increase the chewing efficiency of the system? To address this question we first examine the primitive condition for prey processing representative of many of the past and present predatory amniotes. Because herbivory is expected to be related to improved prey processing in the jaws we review patterns of food processing mechanics in past and present herbivores. Herbivory has appeared numerous times in amniotes and several solutions to the task of chewing plant matter have appeared. Birds have abandoned jaw chewing in favor of a new way to chew--with the gut--so we will detour from the jaws to examine the appearance of gut chewing in the archosaurs. We will then fill in the gaps among amniote taxa with a look at some new data on patterns of prey processing behavior and jaw mechanics in lizards. Finally, we examine evolutionary patterns of amniote feeding mechanism and how correlates of chewing relate to the need to increase the efficiency of prey processing in order to facilitate increased metabolic rate and activity.     

Linking patterns and processes of species diversification in the cone flies Strobilomyia (Diptera: Anthomyiidae)

Phytophagous insects provide useful models for the study of ecological speciation. Much attention has been paid to host shifts, whereas situations where closely related lineages of insects use the same plant during different time periods have been relatively neglected in previous studies of insect diversification. Flies of the genus Strobilomyia are major pests of conifers in Eurasia and North America. They are specialized feeders in cones and seeds of Abies (fir), Larix (larch) ,and Picea (spruce). This close association is accompanied by a large number of sympatric Strobilomyia species coexisting within each tree genus. We constructed a molecular phylogeny with a 1320 base-pair fragment of mitochondrial DNA that demonstrated contrasting patterns of speciation in larch cone flies, as opposed to spruce and fir cone flies; this despite their comparable geographic distributions and similar resource quality of the host. Species diversity is the highest on larch, and speciation is primarily driven by within-host phenological shifts, followed by allopatric speciation during geographical expansion. By contrast, fewer species exploit spruce and fir, and within-host phenological shifts did not occur. This study illustrates within-host adaptive radiation through phenological shifts, a neglected mode of sympatric speciation.     

Aesthetic issues in spatial composition: effects of position and direction on framing single objects

Artists who work in two-dimensional visual media regularly face the problem of how to compose their subjects in aesthetically pleasing ways within a surrounding rectangular frame. We performed psychophysical investigations of viewers' aesthetic preferences for the position and facing direction of single, directed objects (e.g. people, cars, teapots and flowers) within such rectangular frames. Preferences were measured using two-alternative forced-choice preference judgments, the method of adjustment, and free choice in taking photographs. In front-facing conditions, preference was greatest for pictures whose subject was located at or near the center of the frame and decreased monotonically and symmetrically with distance from the center (the center bias). In the left- or right-facing conditions, there was an additional preference for objects to face into rather than out of the frame (the inward bias). Similar biases were evident using a method of adjustment, in which participants positioned objects along a horizontal axis, and in free choice photographs, in which participants were asked to take 'the most aesthetically pleasing picture' they could of everyday objects. The results are discussed as affirming the power of the center and facing direction in the aesthetic biases viewers bring to their appreciation of framed works of visual art (e.g. Alexander, 2002; Arnheim, 1988).     

Behavioural analyses of quinine processing in choice, feeding and learning of larval Drosophila

Gustatory stimuli can support both immediate reflexive behaviour, such as choice and feeding, and can drive internal reinforcement in associative learning. For larval Drosophila, we here provide a first systematic behavioural analysis of these functions with respect to quinine as a study case of a substance which humans report as "tasting bitter". We describe the dose-effect functions for these different kinds of behaviour and find that a half-maximal effect of quinine to suppress feeding needs substantially higher quinine concentrations (2.0 mM) than is the case for internal reinforcement (0.6 mM). Interestingly, in previous studies (Niewalda et al. 2008, Schipanski et al 2008) we had found the reverse for sodium chloride and fructose/sucrose, such that dose-effect functions for those tastants were shifted towards lower concentrations for feeding as compared to reinforcement, arguing that the differences in dose-effect function between these behaviours do not reflect artefacts of the types of assay used. The current results regarding quinine thus provide a starting point to investigate how the gustatory system is organized on the cellular and/or molecular level to result in different behavioural tuning curves towards a bitter tastant.