Small-field Motion Research Articles

Candidate Neural Substrates for Off-Edge Motion Detection in Drosophila

In the fly's visual motion pathways, two cell types-T4 and T5-are the first known relay neurons to signal small-field direction-selective motion responses [1]. These cells then feed into large tangential cells that signal wide-field motion. Recent studies have identified two types of columnar neurons in the second neuropil, or medulla, that relay input to T4 from L1, the ON-channel neuron in the first neuropil, or lamina, thus providing a candidate substrate for the elementary motion detector (EMD) [2]. Interneurons relaying the OFF channel from L1's partner, L2, to T5 are so far not known, however. Here we report that multiple types of transmedulla (Tm) neurons provide unexpectedly complex inputs to T5 at their terminals in the third neuropil, or lobula. From the L2 pathway, single-column input comes from Tm1 and Tm2 and multiple-column input from Tm4 cells. Additional input to T5 comes from Tm9, the medulla target of a third lamina interneuron, L3, providing a candidate substrate for L3's combinatorial action with L2 [3]. Most numerous, Tm2 and Tm9's input synapses are spatially segregated on T5's dendritic arbor, providing candidate anatomical substrates for the two arms of a T5 EMD circuit; Tm1 and Tm2 provide a second. Transcript profiling indicates that T5 expresses both nicotinic and muscarinic cholinoceptors, qualifying T5 to receive cholinergic inputs from Tm9 and Tm2, which both express choline acetyltransferase (ChAT). We hypothesize that T5 computes small-field motion signals by integrating multiple cholinergic Tm inputs using nicotinic and muscarinic cholinoceptors.

Fly VS neurons compared to optimized motion detectors

Event Abstract Back to Event Fly VS neurons compared to optimized motion detectors A function of dendrites is synaptic-integration. The specific electrophysiological dynamics involved in this process have been a subject of neurobiological research for many decades. However, some questions remain unresolved, such as what determines the morphology of dendrites: the need to perform signal transformations or to connect to incoming axons in an efficient manner, or both? We employ a recently developed inverse approach to study the dendritic morphology-function relationship [2]. Briefly, this approach consist of (1) defining a computational function to be performed by a model neuron, (2) optimizing a model neuron endowed with a dendritic morphology to perform the targeted function, and (3) analyze the emerged contingencies to quantify the morphology-function relationship. By specifying a desired function we evidently focus on the functional characteristics of dendrites. We investigated the hypothesized function of the VS cell from the fly lobular plate which is spatio-temporal integration of small-field direction sensitive inputs. This integration step is also referred to as wide-field motion detection, i.e., detection of motion of over the complete visual field of the fly. We constructed a model in which the small-field motion detection is performed by Reichardt detectors [1] and their output was projected in a realistic way onto the model neuron that has to perform the spatio-temporal integration. The output signal of the integration cell is a smooth signal indicating the direction of the movement. The morphology and the distribution of potassium and sodium conductances is optimized by using the inverse approach. We ran three optimization runs for three different velocities of movement. All neurons could perform the spatio-temporal integration well. Moreover, we found that some (5 out of 9) from a qualitative point of view (visually) resembled the VS cells. Moreover, we found similar distribution of ion-channels in all model neurons. Thus, the dendritic morphology is optimized for performing a computational-electrophysiological function instead of only collecting inputs. It can be argued that due to the biologically realistic constraints imposed by the projection of the small-field sensitive inputs onto the model neuron, the neuron is actually forced to take a shape that corresponds to the shape of the true cells. However, since some model neurons had an entirely different morphology than observed in nature, but still performed the function well, we can rule this option out. Hence, we can conclude that dendritic morphology is not only optimized for wiring, but also to perform specific function in some neuronal substrate.

An interactive dynamic analysis and decision support software for MR mammography

A fully automated software is introduced to facilitate MR mammography (MRM) examinations and overcome subjectiveness in diagnosis using normalized maximum intensity–time ratio (nMITR) maps. These maps inherently suppress enhancements due to normal parenchyma and blood vessels that surround lesions and have natural tolerance to small field inhomogeneities and motion artifacts. The classifier embedded within the software is trained with normalized complexity and maximum nMITR of 22 lesions and tested with the features of remaining 22 lesions. Achieved diagnostic performances are 92% sensitivity, 90% specificity, 91% accuracy, 92% positive predictive value and 90% negative predictive value. DynaMammoAnalyst shortens evaluation time considerably and reduces inter and intra-observer variability by providing decision support.

Dynamic properties of large-field and small-field optomotor flight responses in Drosophila

Optomotor flight control in houseflies shows bandwidth fractionation such that steering responses to an oscillating large-field rotating panorama peak at low frequency, whereas responses to small-field objects peak at high frequency. In fruit flies, steady-state large-field translation generates steering responses that are three times larger than large-field rotation. Here, we examine the optomotor steering reactions to dynamically oscillating visual stimuli consisting of large-field rotation, large-field expansion, and small-field motion. The results show that, like in larger flies, large-field optomotor steering responses peak at low frequency, whereas small-field responses persist under high frequency conditions. However, in fruit flies large-field expansion elicits higher magnitude and tighter phase-locked optomotor responses than rotation throughout the frequency spectrum, which may suggest a further segregation within the large-field pathway. An analysis of wing beat frequency and amplitude reveals that mechanical power output during flight varies according to the spatial organization and motion dynamics of the visual scene. These results suggest that, like in larger flies, the optomotor control system is organized into parallel large-field and small-field pathways, and extends previous analyses to quantify expansion-sensitivity for steering reflexes and flight power output across the frequency spectrum.

Small field motion detection in goldfish is red-green color blind and mediated by the M-cone type

Large field motion detection in goldfish, measured in the optomotor response, is based on the L-cone type, and is therefore color-blind (Schaerer & Neumeyer, 1996). In experiments using a two-choice training procedure, we investigated now whether the same holds for the detection of a small moving object (size: 8 mm diameter; velocity: 7 cm/s). In initial experiments, we found that goldfish did not discriminate between a moving and a stationary stimulus, obviously not taking attention to the cue "moving." Therefore, random dot patterns were used in which the stimulus was visible only when moving. Using black and white random dot patterns with variable contrast between 0.2 and 1, we found that the fish could see motion only with high (0.8) contrast. In the decisive experiment, a red-green random dot pattern was used. By keeping the intensity of the red dots constant and reducing the intensity of the green dots, a narrow intensity range was found in which goldfish could no longer discriminate between the moving random dot stimulus in random dot surround and the stationary random dot pattern. The same was the case when a red moving disk was presented in green surround. This is the evidence that object motion is red-green color blind, i.e., color information cannot be used to detect the moving object. Calculations of the cone excitation values revealed that the M-cone type is decisive, as this cone type (and not the L-cone type) is not modulated by that particular red-green pattern in which the moving stimulus was invisible.

Fixation suppression of optokinetic nystagmus modulates cortical visual???vestibular interaction

Water activation positron emission tomography and statistical group analysis were used to evaluate differences in activation-deactivation patterns during small-field visual motion stimulation, eliciting rightward optokinetic nystagmus and its fixation suppression in 12 healthy volunteers. Bilateral patterns of activation in the visual cortex, including the motion-sensitive area MT/V5, and deactivations in an assembly of vestibular areas (posterior insula, thalamus, anterior cingulate gyrus) during optokinetic nystagmus was markedly diminished or totally absent during its fixation suppression. This finding agrees with the concept of a reciprocal inhibitory interaction between the visual-optokinetic and the vestibular systems, which takes place at a lower level during fixation suppression, because the potential mismatch between the two sensory inputs, visual and vestibular, is then reduced.

A Biomimetic VLSI Sensor for Visual Tracking of Small Moving Targets

Taking inspiration from the visual system of the fly, we describe and characterize a monolithic analog very large-scale integration sensor, which produces control signals appropriate for the guidance of an autonomous robot to visually track a small moving target. This sensor is specifically designed to allow such tracking even from a moving imaging platform which experiences complex background optical flow patterns. Based on relative visual motion of the target and background, the computational model implemented by this sensor emphasizes any small-field motion which is inconsistent with the wide-field background motion.

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.

Task-specific association of photoreceptor systems and steering parameters in Drosophila.

Visual motion processing enables moving fruit flies to stabilize their course and altitude and to approach selected objects. Earlier attempts to identify task-specific pathways between two photoreceptor systems (peripheral retinula cells 1-6, and central retinula cells 7 + 8) and three steering parameters (wingstroke asymmetry, abdomen deflection, hindleg deflection) attributed course control and object fixation to peripheral retinula cells 1-6-mediated simultaneous reactions of these parameters. The present investigation includes first results from fixed flying or freely walking ninaE17 mutants which cannot synthesize the peripheral retinula cells 1-6 photoreceptor-specific opsin. Retention of about 12% of the normal course control and about 58% of the object fixation in these flies suggests partial input sharing for both responses and, possibly, a specialization for large-field (peripheral retinula cells 1-6) and small-field (central retinula cells 7 + 8) motion. Such signals must be combined to perceive relative motion between an object and its background. The combining links found in larger species might explain a previously neglected interdependence of course control and object fixation in Drosophila. -Output decomposition revealed an unexpected orchestration of steering. Wingstroke asymmetry and abdomen deflection do not contribute in fixed proportions to the yaw torque of the flight system. Different steering modes seem to be selected according to their actual efficiency under closed-loop conditions and to the degree of intended turning. An easy experimental access to abdominal steering is introduced.

Optic flow representation in the optic lobes of Diptera: modeling innervation matrices onto collators and their evolutionary implications.

A network model of optic flow processing, based on physiological and anatomical features of motion-processing neurons, is used to investigate the role of small-field motion detectors emulating T5 cells in producing optic flow selective properties in wide-field collator neurons. The imposition of different connectivities can mimic variations observed in comparative studies of lobula plate architecture across the Diptera. The results identify two features that are crucial for optic flow selectivity: the broadness of the spatial patterns of synaptic connections from motion detectors to collators, and the relative contributions of excitatory and inhibitory synaptic outputs. If these two aspects of the innervation matrix are balanced appropriately, the network's sensitivity to perturbations in physiological properties of the small-field motion detectors is dramatically reduced, suggesting that sensory systems can evolve robust mechanisms that do not rely upon precise control of network parameters. These results also suggest that alternative lobula plate architectures observed in insects are consistent in allowing optic flow selective properties in wide-field neurons. The implications for the evolution of optic flow selective neurons are discussed.

Neural circuit tuning fly visual interneurons to motion of small objects. I. Dissection of the circuit by pharmacological and photoinactivation techniques.

1. Visual interneurons tuned to the motion of small objects are found in many animal species and are assumed to be the neuronal basis of figure-ground discrimination by relative motion. A well-examined example is the FD1-cell in the third visual neuropil of blowflies. This cell type responds best to motion of small objects. Motion of extended patterns elicits only small responses. As a neuronal mechanism that leads to such a response characteristic, it was proposed that the FD1-cell is inhibited by the two presumably GABAergic and, thus, inhibitory CH-cells, the VCH- and the DCH-cell. The CH-cells respond best to exactly that type of motion by which the activity of the FD1-cell is reduced. The hypothesis that the CH-cells inhibit the FD1-cell and, thus, mediate its selectivity to small moving objects was tested by ablating the CH-cells either pharmacologically or by photoinactivation. 2. After application of the gamma-aminobutyric acid (GABA) antagonist picrotoxinin, the FD1-cell responds more strongly to large-field than to small-field motion, i.e., it has lost its small-field selectivity. This suggests that the tuning of the FD1-cell to small moving objects relies on a GABAergic mechanism and, thus, most likely on the CH-cells. 3. The role of each CH-cell for small-field tuning was determined by inactivating them individually. They were injected with a fluorescent dye and then ablated by laser illumination. Only photoinactivation of the VCH-cell eliminated the specific selectivity of the FD1-cell for small-field motion. Ablation of the DCH-cell did not significantly change the response characteristic of the FD1-cell. This reveals the important role of the VCH-cells in mediating the characteristic sensitivity of the FD1-cell to motion of small objects. 4. The FD1-cell is most sensitive to motion of small objects in the ventral part of the ipsilateral visual field, whereas motion in the dorsal part influences the cell only weakly. This specific feature fits well to the sensitivity of the VCH-cell to ipsilateral motion that is most pronounced in the ventral part of the visual field. The spatial sensitivity distribution of the FD1-cell matches also the characteristics of figure-ground discrimination and fixation behavior.

Photo-ablation of single neurons in the fly visual system reveals neural circuit for the detection of small moving objects

Many animals use relative motion to segregate objects from their background [21, 26, 28, 31, 33]. Nerve cells tuned to this visual cue have been found in various animal groups, such as insects [3, 4, 6, 24, 25], amphibians [32], birds [12, 13] and mammals [1, 14]. Well examined examples are the figure detection (FD) cells in the visual system of the blowfly [6, 11]. The mechanism that tunes a particular FD-cell, the FD1-cell, to small-field motion is analyzed by injecting individual visual interneurons with a fluorescent dye and ablating them by illumination with a laser beam. In this way, it is shown that the FD1-cell acquires its specific spatial tuning by inhibitory input from an identified GABAergic cell, the ventral centrifugal horizontal (VCH)-cell which is most sensitive to coherent large-field motion in front of both eyes. For the first time, the detection of small objects by evaluation of their motion parallax, thus, can be attributed to synaptic interactions between identified neurons.

Descending neurons supplying the neck and flight motor of diptera: Physiological and anatomical characteristics

In Diptera, dorsal neuropils of the pro-, meso-, and metathoracic ganglia supply motor neurons to neck and flight muscles. Motor circuits are supplied by more than 50 pairs of descending neurons (DNs) whose dendritic trees in the brain are restricted to dorsal neuropils of the deutocerebrum where they are grouped together into discrete clusters. Each cluster is visited by wide-field motion-sensitive neurons and by morphologically small-field retinotopic elements. This organization suggests that flight descending neurons should respond to complex stimuli reflecting panoramic movement and small-field motion. Intracellular recordings, combined with dye filling, confirm this. Certain descending neurons responding to visual flow fields terminate bilaterally in superficial pterothoracic neuropils, at the level of indirect (power) flight muscle motor neurons. Other DNs terminate laterally, and provide segmental collaterals to areas containing neck and direct (steering) flight muscle motor neurons. Such DNs are activated by wide-field directional stimuli corresponding to pitch, roll, or yaw, and to small-field stimuli. Appropriate directional mechanosensory stimuli also activate dorsal descending neurons. The significance of dorsal descending neurons for the control of flight is discussed and compared with studies on course deviation neurons in other insects. It is suggested that, in Diptera, dorsal descending neurons may separately be involved in the control of velocity, stabilization, and steering manoeuvres.

Spatial interactions in the fly visual system leading to selectivity for small-field motion

Mise en evidence pharmacologique et electrophysiologique de la sensibilite selective de cellules du ganglion visuel aux objets se deplacant lentement

Visual afferences to flight steering muscles controlling optomotor responses of the fly.

In tethered flying house-flies (Musca domestica) visually induced turning reactions were monitored under open-loop conditions simultaneously with the spike activity of four types of steering muscles (M.b1, M.b2, M.I1, M.III1). Specific behavioral response components are attributed to the activity of particular muscles. Compensatory optomotor turning reactions to large-field image displacements mainly occur when the stimulus pattern oscillates at low frequencies. In contrast, turning responses towards objects are preferentially induced by motion of relatively small stimuli at high oscillation frequencies. The different steering muscles seem to be functionally specialized in that they contribute to the control of these behavioral responses in different ways. The muscles I1, III1 and b2 are preferentially active during small-field motion at high oscillation frequencies. They are much less active during small-field motion at low oscillation frequencies and large-field motion at all oscillation frequencies which were tested. M.b2 is most extreme in this respect. These steering muscles thus mediate mainly turns towards objects. In contrast, M.b1 responds best during large-field motion at low oscillation frequencies and, thus, is appropriate to control compensatory optomotor responses. However, the activity of this muscle is also strongly modulated during small-field motion at high oscillation frequencies and, therefore, may be involved also in the control of turns towards objects. These functional specializations of the different steering muscles in mediating different behavioral response components are related to the properties of two parallel visual pathways that are selectively tuned to large-field and small-field motion, respectively.

The dipteran ?Giant fibre? pathway: neurons and signals

1. The uniquely identifiable pair of giant descending neurons ofMusca domestica andCalliphora erythrocephala are compared and described in relation to homologues inDrosophila. 2. Cobalt coupling in the giant fibre system suggests that giant descending neurons receive inputs from antennal mechanosensory afferents and small-field visual interneurons. 3. InMusca andCalliphora, terminals of giant descending neurons invade several discrete areas of neuropil. This is in contrast toDrosophila where homologous neurons have a relatively simple terminal. 4. Despite differences in morphology, in all three species a homologous terminal region is cobalt-coupled to the largest of three motorneurons supplying the second leg's tergotrochanteral muscle. 5. Sensory connections revealed anatomically were confirmed electrophysiologically by intracellular recording and dye-filling. Mechanosensory inputs from the ipsilateral antenna, and small field motion stimuli, or light ‘on’ and ‘off’ stimuli to the ipsilateral compound eyes, produce subthreshold activation in the giant descending neuron. 6. As inDrosophila, light ‘on’ or ‘off’ stimuli presented to white-eyed mutants ofMusca andCalliphora elicit a spiking response in the giant descending neuron. In red-eyed flies, spikes could only be routinely induced by electrical stimulation across the head between the compound eyes or by releasing the cell from hyperpolarization. 7. Double recordings from the giant (intracellular combined with lucifer or cobalt iontophoresis for cell identification) and from the tergotrochanteral motorneuron (extracellular in muscle) show that a spike in the giant neuron is usually sufficient to drive a spike in the tergotrochanteral muscle. Latencies are short, as reported inDrosophila. Releasing the giant from hyperpolarization can result in a motorneuron spike in the absence of a spike in the giant: this suggests the presence of an electrical synapse. 8. Spiking in the tergotrochanteral muscle and the giant can occur independently of each other. Thus, this interneuron alone is neither necessary nor invariably sufficient for initiating ‘escape behaviour’ in the species studied. This is also corroborated by the structure of tergotrochanteral motorneurons whose extensive dendrites receive a variety of other inputs.

The three-dimensional optomotor torque system ofDrosophila melanogaster

The well known optomotor yaw torque response in flies is part of a 3-dimensional system. Optomotor responses around the longitudinal and transversal body axes (roll and pitch) with strinkingly similar properties to the optomotor yaw response are described here forDrosophila melanogaster. Stimulated by visual motion from a striped drum rotating around an axis aligned with the measuring axis, a fly responds with torque of the same polarity as that of the rotation of the pattern. In this stimulus situation the optomotor responses for yaw, pitch and roll torque have about the same amplitudes and dynamic properties (Fig. 2). Pronounced negative responses are measured with periodic gratings of low pattern wavelengths due to geometrical interference (Fig. 3). The responses depend upon the contrast frequency rather than the angular velocity of the pattern (Fig. 4). Like the optomotor yaw response, roll and pitch responses can be elicited by small field motion in most parts of the visual field; only for motion below and behind the fly roll and pitch responses have low sensitivity. The mutantoptomotor-blind H31 (omb H31) in which the giant neurones of the lobula plate are missing or severely reduced, is impaired in all 3 optomotor torque responses (Fig. 5) whereas other visual responses like the optomotor lift/thrust response and the landing response (elicited by horizontal front-to-back motion) are not affected (Heisenberg et al. 1978). We propose that the lobula plate giant neurons mediate optomotor torque responses and that the VS-cells in particular are involved in roll and pitch but not in lift/thrust control. This hypothesis accommodates various electrophysiological and anatomical observations about these neurons in large flies.

Behavior of liquid metal stream in a transverse magnetic field

This is a theoretical study of the effect of a transverse magnetic field on the flow characteristics of a two-dimensional laminar submerged jet stream of an electrically conducting, viscous, incompressible fluid. The analysis may be applicable to liquid metal jet streams for two limiting cases: (i) small magnetic field or (ii) slow motion. In either limiting case, an increase in the intensity of the magnetic field is shown to enhance the extent of velocity decay in the downstream direction.