Martin Heisenberg

Mushroom body memoir: from maps to models

Genetic intervention in the fly Drosophila melanogaster has provided strong evidence that the mushroom bodies of the insect brain act as the seat of a memory trace for odours. This localization gives the mushroom bodies a place in a network model of olfactory memory that is based on the functional anatomy of the olfactory system. In the model, complex odour mixtures are assumed to be represented by activated sets of intrinsic mushroom body neurons. Conditioning renders an extrinsic mushroom-body output neuron specifically responsive to such a set. Mushroom bodies have a second, less understood function in the organization of the motor output. The development of a circuit model that also addresses this function might allow the mushroom bodies to throw light on the basic operating principles of the brain.

Dopamine and Octopamine Differentiate between Aversive and Appetitive Olfactory Memories in Drosophila

The catecholamines play a major role in the regulation of behavior. Here we investigate, in the fly Drosophila melanogaster, the role of dopamine and octopamine (the presumed arthropod homolog of norepinephrine) during the formation of appetitive and aversive olfactory memories. We find that for the formation of both types of memories, cAMP signaling is necessary and sufficient within the same subpopulation of mushroom-body intrinsic neurons. On the other hand, memory formation can be distinguished by the requirement for different catecholamines, dopamine for aversive and octopamine for appetitive conditioning. Our results suggest that in associative conditioning, different memories are formed of the same odor under different circumstances, and that they are linked to the respective motivational systems by their specific modulatory pathways.

Distinct memory traces for two visual features in the Drosophila brain

The fly Drosophila melanogaster can discriminate and remember visual landmarks. It analyses selected parts of its visual environment according to a small number of pattern parameters such as size, colour or contour orientation, and stores particular parameter values. Like humans, flies recognize patterns independently of the retinal position during acquisition of the pattern (translation invariance). Here we show that the central-most part of the fly brain, the fan-shaped body, contains parts of a network mediating visual pattern recognition. We have identified short-term memory traces of two pattern parameters—elevation in the panorama and contour orientation. These can be localized to two groups of neurons extending branches as parallel, horizontal strata in the fan-shaped body. The central location of this memory store is well suited to mediate translational invariance.

Context generalization in Drosophila visual learning requires the mushroom bodies

The world is permanently changing. Laboratory experiments on learning and memory normally minimize this feature of reality, keeping all conditions except the conditioned and unconditioned stimuli as constant as possible. In the real world, however, animals need to extract from the universe of sensory signals the actual predictors of salient events by separating them from non-predictive stimuli (context). In principle, this can be achieved ifonly those sensory inputs that resemble the reinforcer in theirtemporal structure are taken as predictors. Here we study visual learning in the fly Drosophila melanogaster, using a flight simulator,, and show that memory retrieval is, indeed, partially context-independent. Moreover, we show that the mushroom bodies, which are required for olfactory but not visual or tactile learning, effectively support context generalization. In visual learning in Drosophila, it appears that a facilitating effect of context cues for memory retrieval is the default state, whereas making recall context-independent requires additional processing.

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

BackgroundCurrent 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.ResultsHere we present a platform-independent framework based on Java and Java 3D for accelerated rendering of biological images. Our framework is seamlessly integrated into ImageJ, a free image processing package with a vast collection of community-developed biological image analysis tools. Our framework enriches the ImageJ software libraries with methods that greatly reduce the complexity of developing image analysis tools in an interactive 3D visualization environment. In particular, we provide high-level access to volume rendering, volume editing, surface extraction, and image annotation. The ability to rely on a library that removes the low-level details enables concentrating software development efforts on the algorithm implementation parts.ConclusionsOur framework enables biomedical image software development to be built with 3D visualization capabilities with very little effort. We offer the source code and convenient binary packages along with extensive documentation at http://3dviewer.neurofly.de.

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. To address such issues, a consortium of neurobiologists studying arthropod brains, the Insect Brain Name Working Group, has established the present hierarchical nomenclature system, using the brain of Drosophila melanogaster as the reference framework, while taking the brains of other taxa into careful consideration for maximum consistency and expandability. The following summarizes the consortiums nomenclature system and highlights examples of existing ambiguities and remedies for them. This nomenclature is intended to serve as a standard of reference for the study of the brain of Drosophila and other insects.

Dissection of the Peripheral Motion Channel in the Visual System of Drosophila melanogaster

In the eye, visual information is segregated into modalities such as color and motion, these being transferred to the central brain through separate channels. Here, we genetically dissect the achromatic motion channel in the fly Drosophila melanogaster at the level of the first relay station in the brain, the lamina, where it is split into four parallel pathways (L1-L3, amc/T1). The functional relevance of this divergence is little understood. We now show that the two most prominent pathways, L1 and L2, together are necessary and largely sufficient for motion-dependent behavior. At high pattern contrast, the two pathways are redundant. At intermediate contrast, they mediate motion stimuli of opposite polarity, L2 front-to-back, L1 back-to-front motion. At low contrast, L1 and L2 depend upon each other for motion processing. Of the two minor pathways, amc/T1 specifically enhances the L1 pathway at intermediate contrast. L3 appears not to contribute to motion but to orientation behavior.

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. RESULTS An automated video analysis of aggression in male Drosophila has been developed, rendering aggression accessible to high-throughput studies. The software detects the lunge, a conspicuous behavioral act unique to aggression. In lunging, the aggressor rears up on his hind legs and snaps down on his opponent. By using the software to eliminate confounding effects, we now show that aggression is almost abolished in mutant males lacking octopamine. This suppression is independent of whether tyramine, the precursor of octopamine, is increased or also depleted. Restoring octopamine synthesis in the brain either throughout life or in adulthood leads to a partial rescue of aggression. Finally, neuronal silencing of octopaminergic and tyraminergic neurons almost completely abolishes lunges. CONCLUSIONS Octopamine modulates Drosophila aggression. Genetically depleting the animal of octopamine downregulates lunge frequency without a sizable effect on the lunge motor program. This study provides access to the neuronal circuitry mediating this modulation.

Central complex substructures are required for the maintenance of locomotor activity in Drosophila melanogaster.

Abstract In Drosophila melanogaster, former studies based on structural brain mutants have suggested that the central complex is a higher control center of locomotor behavior. Continuing this investigation we studied the effect of the central complex on the temporal structure of spontaneous locomotor activity in the time domain of a few hours. In an attempt to dissect the internal circuitry of the central complex we perturbed a putative local neuronal network connecting the four neuropil regions of the central complex, the protocerebral bridge, the fan-shape body, the noduli and the ellipsoid body. Two independent and non-invasive methods were applied: mutations affecting the neuroarchitecture of the protocerebral bridge, and the targeted expression of tetanus toxin in small subsets of central complex neurons using the binary enhancer trap P[GAL4] system. All groups of flies with a disturbed component of this network exhibited a common phenotype: a drastic decrease in locomotor activity. While locomotor activity was still clustered in bouts and these were initiated at the normal rate, their duration was reduced. This finding suggests that the bridge and some of its neural connections to the other neuropil regions of the central complex are required for the maintenance but not the initiation of walking.

An engram found? Evaluating the evidence from fruit flies

Is it possible to localize a memory trace to a subset of cells in the brain? If so, it should be possible to show: first, that neuronal plasticity occurs in these cells. Second, that neuronal plasticity in these cells is sufficient for memory. Third, that neuronal plasticity in these cells is necessary for memory. Fourth, that memory is abolished if these cells cannot provide output during testing. And fifth, that memory is abolished if these cells cannot receive input during training. With regard to olfactory learning in flies, we argue that the notion of the olfactory memory trace being localized to the Kenyon cells of the mushroom bodies is a reasonable working hypothesis.