Memory, anticipation, action - working with Troy D. Zars.

We present here our reflections on the scientific work of the late Troy D. Zars (1967 - 2018), on what it was like to work with him, and what it means to us. A common theme running through his work is that memory systems are not for replaying the past.

A Toll-receptor map underlies structural brain plasticity.

Experience alters brain structure, but the underlying mechanism remained unknown. Structural plasticity reveals that brain function is encoded in generative changes to cells that compete with destructive processes driving neurodegeneration. At an adult critical period, experience increases fiber number and brain size in .

Multi-stability with ambiguous visual stimuli in Drosophila orientation behavior.

It is widely accepted for humans and higher animals that vision is an active process in which the organism interprets the stimulus. To find out whether this also holds for lower animals, we designed an ambiguous motion stimulus, which serves as something like a multi-stable perception paradigm in Drosophila behavior. Confronted with a uniform panoramic texture in a closed-loop situation in stationary flight, the flies adjust their yaw torque to stabilize their virtual self-rotation.

Starvation promotes odor/feeding-time associations in flies.

Starvation causes a motivational state that facilitates diverse behaviors such as feeding, walking, and search. Starved can form odor/feeding-time associations but the role of starvation in encoding of "time" is poorly understood. Here we show that the extent of starvation is correlated with the fly's ability to establish odor/feeding-time memories.

Inescapable Stress Changes Walking Behavior in Flies - Learned Helplessness Revisited.

Like other animals flies develop a state of learned helplessness in response to unescapable aversive events. To show this, two flies, one 'master', one 'yoked', are each confined to a dark, small chamber and exposed to the same sequence of mild electric shocks. Both receive these shocks when the master fly stops walking for more than a second.

Visual Attention in Flies-Dopamine in the Mushroom Bodies Mediates the After-Effect of Cueing.

Visual environments may simultaneously comprise stimuli of different significance. Often such stimuli require incompatible responses. Selective visual attention allows an animal to respond exclusively to the stimuli at a certain location in the visual field.

Vision in Flies: Measuring the Attention Span.

A visual stimulus at a particular location of the visual field may elicit a behavior while at the same time equally salient stimuli in other parts do not. This property of visual systems is known as selective visual attention (SVA). The animal is said to have a focus of attention (FoA) which it has shifted to a particular location.

Flies remember the time of day.

The circadian clock enables organisms to anticipate daily environmental cycles and drives corresponding changes in behavior [1, 2]. Such endogenous oscillators also enable animals to display time-specific memory [1, 3-5]. For instance, mice and honeybees associate the location of a stimulus (like food or mate) with a certain time of day (time-place learning) [6, 7].

Outcome learning, outcome expectations, and intentionality in Drosophila.

An animal generates behavioral actions because of the effects of these actions in the future. Occasionally, the animal may generate an action in response to a certain event or situation. If the outcome of the action is adaptive, the animal may keep this stimulus-response link in its behavioral repertoire, in case the event or situation occurs again.

Central complex and mushroom bodies mediate novelty choice behavior in Drosophila.

Novelty choice, a visual paired-comparison task, for the fly Drosophila melanogaster is studied with severely restrained single animals in a flight simulator. The virtual environment simulates free flight for rotation in the horizontal plane. The behavior has three functional components: visual azimuth orientation, working memory, and pattern discrimination (perception).

The beauty of the network in the brain and the origin of the mind in the control of behavior.

Behavior is not adequately described as a stimulus-response process. It is initiated by the animal and is generated because of its expected outcome in the future. The outcome can be good or bad for the animal.

A systematic nomenclature for the insect brain.

Despite the importance of the insect nervous system for functional and developmental neuroscience, descriptions of insect brains have suffered from a lack of uniform nomenclature. Ambiguous definitions of brain regions and fiber bundles have contributed to the variation of names used to describe the same structure. The lack of clearly determined neuropil boundaries has made it difficult to document precise locations of neuronal projections for connectomics study.

Flies cope with uncontrollable stress by learned helplessness.

In a wide range of animals, uncontrollable stressful events can induce a condition called "learned helplessness." In mammals it is associated with low general activity, poor learning, disorders of sleep and feeding, ulcers, and reduced immune status, as well as with increased serotonin in parts of the brain. It is considered an animal model of depression in humans.

'Humans and other animals'-on the scope of brain science.

Abstract: This essay is dedicated to Obaid on the occasion of his 80th birthday. We both worked on the behavior of Drosophila and on what underlies behavior in the fly brain. Is that the fly's mind? The essay is about some limitations of brain science.

Photoreceptors and neural circuitry underlying phototaxis in insects.

Visual behavior of insects has long been studied, but it is only recently that a wide variety of genetic tools has become available for its analysis. Perhaps the most basic visual behaviour is phototaxis, locomotion towards a source of light. It is known in many insects and has been studied for over a century but the neural network underlying it is little understood.

Attracting the attention of a fly.

Organisms with complex visual systems rarely respond to just the sum of all visual stimuli impinging on their eyes. Often, they restrict their responses to stimuli in a temporarily selected region of the visual field (selective visual attention). Here, we investigate visual attention in the fly Drosophila during tethered flight at a torque meter.

A high-level 3D visualization API for Java and ImageJ.

Background: Current imaging methods such as Magnetic Resonance Imaging (MRI), Confocal microscopy, Electron Microscopy (EM) or Selective Plane Illumination Microscopy (SPIM) yield three-dimensional (3D) data sets in need of appropriate computational methods for their analysis. The reconstruction, segmentation and registration are best approached from the 3D representation of the data set.

Results: Here we present a platform-independent framework based on Java and Java 3D for accelerated rendering of biological images.

Contribution of photoreceptor subtypes to spectral wavelength preference in Drosophila.

The visual systems of most species contain photoreceptors with distinct spectral sensitivities that allow animals to distinguish lights by their spectral composition. In Drosophila, photoreceptors R1-R6 have the same spectral sensitivity throughout the eye and are responsible for motion detection. In contrast, photoreceptors R7 and R8 exhibit heterogeneity and are important for color vision.

P90 Ribosomal s6 kinase 2 negatively regulates axon growth in motoneurons.

Mutations in Ribosomal s6 kinase 2 (Rsk2) are associated with severe neuronal dysfunction in Coffin-Lowry syndrome (CLS) patients, flies and mice. So far, the mechanisms of how Rsk2 regulates development, maintenance and activity of neurons are not understood. We have investigated the consequences of Rsk2 deficiency in mouse spinal motoneurons.

Drosophila RSK negatively regulates bouton number at the neuromuscular junction.

Ribosomal S6 kinases (RSKs) are growth factor-regulated serine-threonine kinases participating in the RAS-ERK signaling pathway. RSKs have been implicated in memory formation in mammals and flies. To characterize the function of RSK at the synapse level, we investigated the effect of mutations in the rsk gene on the neuromuscular junction (NMJ) in Drosophila larvae.

Distinct memories of odor intensity and quality in Drosophila.

Even in a simple Pavlovian memory task an animal may form several associations that can be independently assessed by the appropriate tests. Studying conditioned odor discrimination of the fruit fly Drosophila melanogaster we found that animals store quality and intensity of an odor as separate memory traces. The trace of odor intensity is short-lived, decaying in <3 h.

Motion vision is independent of color in Drosophila.

Whether motion vision uses color contrast is a controversial issue that has been investigated in several species, from insects to humans. We used Drosophila to answer this question, monitoring the optomotor response to moving color stimuli in WT and genetic variants. In the fly eye, a motion channel (outer photoreceptors R1-R6) and a color channel (inner photoreceptors R7 and R8) have been distinguished.

Octopamine in male aggression of Drosophila.

Background: In mammals and humans, noradrenaline is a key modulator of aggression. Octopamine, a closely related biogenic amine, has been proposed to have a similar function in arthropods. However, the effect of octopamine on aggressive behavior is little understood.