CiteULike: brembs's mushroom

The remote roots of consciousness in fruit-fly selective attention?

B van Swinderen — 2008-07-30T12:57:58-00:00

Bioessays, Vol. 27, No. 3. (2005), 321-330.

A mechanistic study of consciousness need not be confined to human complexity. Other animals also display key behaviors and responses that have long been intimately tied to the measure of consciousness in humans. Among them are some very well-defined and measurable endpoints: selective attention, sleep and general anesthesia. That these three variables associated with changes in consciousness might exist even in a fruit-fly does not necessarily imply that a fly is "conscious", but it does suggest that some of the problems central to the field of consciousness studies could be investigated in a model organism such as Drosophila melanogaster. Demonstrating suppression of unattended stimuli, which is central to attention studies in humans, is now possible in Drosophila by measuring neural correlates of visual selection. By combining such studies with an eventual understanding of suppression in other arousal states in the fly, such as sleep and general anesthesia, we might be unraveling mechanisms relevant to consciousness as well. (C) 2005 Wiley Periodicals, Inc.

Extinction antagonizes olfactory memory at the subcellular level

M Schwaerzel — 2008-07-30T12:57:34-00:00

Neuron, Vol. 35, No. 5. (2002), 951-60.

Memory loss occurs by diverse mechanisms, as different time constants of performance decrement and sensitivities to experimental manipulations suggest. While the phenomena of memory decay, interference, and extinction are well established behaviorally, little is known about them at the circuit or molecular level. In Drosophila, odorant memories lasting up to 3 hr can be localized to mushroom body Kenyon cells, a single neuronal level in the olfactory pathway. The plasticity underlying this memory trace can be induced without Kenyon cell synaptic output. Experimental extinction, i.e., presentation of the conditioned stimulus without the reinforcer, reduces memory performance and does so at the same circuit level as memory formation. Thus, unreinforced presentation of learned odorants antagonizes intracellularly the signaling cascade underlying memory formation.

Memories in Drosophila heat-box learning

G Putz — 2008-07-30T12:57:03-00:00

Learn Mem, Vol. 9, No. 5. (2002), 349-59.

Learning and memory processes of operant conditioning in the heat-box are analyzed. In a search for conditioning parameters leading to high retention scores, intermittent training is shown to give better results than those of continuous training. Immediate retention tests contain two memory components, a spatial preference for one side of the chamber and a "stay-where-you-are-effect." Intermittent training strengthens the latter. In the second part, memory dynamics is investigated. Flies are trained in one chamber and tested in a second one after a brief reminder training. With this direct transfer, memory scores reflect an associative learning process in the first chamber. To investigate memory retention after extended time periods, indirect transfer experiments are performed. The fly is transferred to a different environment between training and test phases. With this procedure, an aftereffect of the training can still be observed 2 h later. Surprisingly, exposure to the chamber without conditioning also leads to a memory effect in the indirect transfer experiment. This exposure effect reveals a dispositional change that facilitates operant learning during the reminder training. The various memory effects are independent of the mushroom bodies.

Oscillations and sparsening of odor representations in the mushroom body

J Perez-Orive — 2008-07-30T12:56:57-00:00

Science, Vol. 297, No. 5580. (2002), 359-65.

In the insect olfactory system, oscillatory synchronization is functionally relevant and reflects the coherent activation of dynamic neural assemblies. We examined the role of such oscillatory synchronization in information transfer between networks in this system. The antennal lobe is the obligatory relay for olfactory afferent signals and generates oscillatory output. The mushroom body is responsible for formation and retrieval of olfactory and other memories. The format of odor representations differs significantly across these structures. Whereas representations are dense, dynamic, and seemingly redundant in the antennal lobe, they are sparse and carried by more selective neurons in the mushroom body. This transformation relies on a combination of oscillatory dynamics and intrinsic and circuit properties that act together to selectively filter and synthesize the output from the antennal lobe. These results provide direct support for the functional relevance of correlation codes and shed some light on the role of oscillatory synchronization in sensory networks.

Spatiotemporal rescue of memory dysfunction in Drosophila

SE Mcguire — 2008-07-30T12:56:23-00:00

Science, Vol. 302, No. 5651. (2003), 1765-8.

We have developed a method for temporal and regional gene expression targeting (TARGET) in Drosophila and show the simultaneous spatial and temporal rescue of a memory defect. The transient expression of the rutabaga-encoded adenylyl cyclase in the mushroom bodies of the adult brain was necessary and sufficient to rescue the rutabaga memory deficit, which rules out a developmental brain defect in the etiology of this deficit and demonstrates an acute role for rutabaga in memory formation in these neurons. The TARGET system offers general utility in simultaneously addressing issues of when and where gene products are required.

The power law distribution for walking-time intervals correlates with the ellipsoid-body in Drosophila

JR Martin — 2008-07-30T12:56:19-00:00

J. Neurogenet., Vol. 15, No. 3-4. (2001), 205-219.

The temporal properties of a variety of behavioral traits obey power law distributions, a property often referred to as fractal. We recently showed that the temporal pattern of locomotor activity of the fruitfly Drosophila melanogaster follows this distribution. Although an increasing number of such fractal patterns are being discovered, the brain areas and neuronal networks responsible remain unknown. In this study, we show that specifically blocking synapses established by neurons of the Drosophila ellipsoid-body, a substructure of the central complex in the brain, leads to a loss of the fractal properties in the temporal pattern. We conclude that the temporal fractal pattern of locomotor activity is regulated in the ellipsoid-body.

Deconstructing memory in Drosophila

C Margulies — 2008-07-30T12:56:18-00:00

Curr Biol, Vol. 15, No. 17. (2005), R700-13.

Unlike most organ systems, which have evolved to maintain homeostasis, the brain has been selected to sense and adapt to environmental stimuli by constantly altering interactions in a gene network that functions within a larger neural network. This unique feature of the central nervous system provides a remarkable plasticity of behavior, but also makes experimental investigations challenging. Each experimental intervention ramifies through both gene and neural networks, resulting in unpredicted and sometimes confusing phenotypic adaptations. Experimental dissection of mechanisms underlying behavioral plasticity ultimately must accomplish an integration across many levels of biological organization, including genetic pathways acting within individual neurons, neural network interactions which feed back to gene function, and phenotypic observations at the behavioral level. This dissection will be more easily accomplished for model systems such as Drosophila, which, compared with mammals, have relatively simple and manipulable nervous systems and genomes. The evolutionary conservation of behavioral phenotype and the underlying gene function ensures that much of what we learn in such model systems will be relevant to human cognition. In this essay, we have not attempted to review the entire Drosophila memory field. Instead, we have tried to discuss particular findings that provide some level of intellectual synthesis across three levels of biological organization: behavior, neural circuitry and biochemical pathways. We have attempted to use this integrative approach to evaluate distinct mechanistic hypotheses, and to propose critical experiments that will advance this field.

Hydroxyurea-induced partial mushroom body ablation in the honeybee Apis mellifera: volumetric analysis and quantitative protein determination

D Malun — 2008-07-30T12:56:18-00:00

J Neurobiol, Vol. 50, No. 1. (2002), 31-44.

Hydroxyurea (HU) treatment of first instar honeybee larvae was previously shown to cause mushroom body (MB) ablations. Predominantly, either one or both median MB subunits were ablated. This prompted us to analyze the effects of asymmetrical or symmetrical HU-induced MB ablation on both the morphology of the brain and on the level of three proteins (synapsin, PKA RII, and PKC), which are considered to play a role in synaptic plasticity, learning, and memory. In brains with one median MB subunit missing the volume of the overall MB calyx neuropil in the lesioned side was diminished by 35%. This strong reduction occurred although the remaining lateral MB calyx of the lesioned brain side was found to be significantly larger than that of the intact side. Accordingly, in brains with both median MB subunits missing the size of the remaining lateral calyces increased. The various types of MB ablation differentially affected the amounts of synapsin, PKA RII, and PKC expressed in the central brain. In animals with bilateral and thus symmetrical MB ablation (both median calyces ablated) the protein amount was found to be similar to that in control animals. However, unilateral MB ablation causes an increase in the amounts of the tested proteins in the intact brain side, while the levels in the ablated side were the same as in control animals. These findings not only show that HU-induced ablation of MB subunits is accompanied by volume changes and by changes in protein expression, but also suggest that these processes are highly regulated between the brain sides. The latter is of general importance in understanding the potential contribution of the MB subunits to learning and memory and their interaction between the brain sides.

Hydroxyurea-induced partial mushroom body ablation does not affect acquisition and retention of olfactory differential conditioning in honeybees

D Malun — 2008-07-30T12:56:18-00:00

J Neurobiol, Vol. 53, No. 3. (2002), 343-60.

The mushroom bodies (MBs), a paired structure in the insect brain, play a major role in storing and retrieving olfactory memories. We tested whether olfactory learning and odor processing is impaired in honeybees in which MB subunits were partially ablated. Using hydroxyurea (HU) to selectively kill proliferating cells, we created honeybees with varying degrees of MB lesions. Three-dimensional reconstructions of brains were generated to analyze the drug-induced morphological changes. These reconstructions show that, with few exceptions, only the MBs were affected by the drug, while other brain areas remained morphometrically intact. Typically, lesions affected only the MB in one hemisphere of the brain. To preclude HU-induced physiologic deficits in the antennal lobe (AL) affecting olfactory learning, we measured the responses to odors in the AL using an in vivo calcium imaging approach. The response patterns did not differ between the AL of intact versus ablated brain sides within respective specimens. We, therefore, carried out side-specific classical discriminative olfactory conditioning of the proboscis extension reflex (PER) with control bees and with HU-treated bees with or without MB ablations. All experimental groups learned equally to discriminate and respond to a rewarded (CS+) but not to an unrewarded (CS-) conditioned stimulus during acquisition and retention tests. Thus, our results indicate that partial MB lesions do not affect this form of elemental olfactory learning.

Partial unilateral lesions of the mushroom bodies affect olfactory learning in honeybees Apis mellifera L

B Komischke — 2008-07-30T12:55:44-00:00

Eur J Neurosci, Vol. 21, No. 2. (2005), 477-85.

The mushroom bodies (MBs) are central structures in the insect brain that have been associated with olfactory learning and memory. Here we used hydroxyurea (HU) to treat honeybee larvae and induce partial MB ablations at the adult stage. We studied olfactory learning in honeybees with unilateral loss of the median calyces of their MBs and compared their ability to solve different forms of olfactory discrimination. When odorants were delivered in a side-specific manner, ablated bees could not solve either discrimination of the unambiguous problem (Paradigm 1: A+, B- on one antenna, C+, D- on the other; A+B-/C+D-) whereas they could solve at least one of both discriminations of the ambiguous problem (Paradigm 2: A+B-/A-B+), namely that proposed to their intact brain side. Non-ablated bees could learn side-specific discriminations on both brain sides. When odorants were delivered simultaneously to both antennae (Paradigm 3: A+B-C+D-), HU-ablated bees learned slower than HU-normal bees. Thus, in all three paradigms, the unilateral loss of a median calyx affected olfactory learning. We propose that the MBs are required for solving elemental olfactory tasks whose complexity is increased by the number of stimuli involved and that MB ablations could have an effect on the inhibition of information exchange between brain hemispheres.

Expression of a D1 dopamine receptor dDA1/DmDOP1 in the central nervous system of Drosophila melanogaster

YC Kim — 2008-07-30T12:55:41-00:00

Gene Expr. Patterns, Vol. 3, No. 2. (2003), 237-245.

The diverse physiological effects of dopamine are mediated by multiple receptor systems. The dDA1 represents one of the Drosophila dopamine receptors that activate the cAMP cascade. To gain insight into the role of dDA1, we generated a polyclonal antibody against the unique sequence in dDA1and investigated dDA1 distribution in the central nervous system (CNS) of Drosophila melanogaster. In both larval and adult CNS pronounced dDA1 immunoreactivity was present in the neuropil of the mushroom bodies, a brain structure crucial for learning and memory in insects, and four unpaired neurons in each thoracic segment. In addition, the larval abdominal ganglion contained two dDA1 cells in each segment. This expression pattern appeared to be maintained in the condensed adult abdominal ganglion although the precise number and the intensity of staining were somewhat variable. The adult CNS also exhibited intense dDA1 immunoreactivity in the central complex, a structure controlling higher-order motor function, moderate expression in several neurosecretory cells, and weak staining in two unpaired neurons in the mesothoracic neuromere. The dDA1 expression in these areas was only detected in adult, but not in third instar larval CNS. (C) 2003 Elsevier Science B.V. All rights reserved.

Diverse odor-conditioned memories require uniquely timed dorsal paired medial neuron output

AC Keene — 2008-07-30T12:55:38-00:00

Neuron, Vol. 44, No. 3. (2004), 521-33.

Amnesiac mutant flies have an olfactory memory defect. The amn gene encodes a homolog of vertebrate pituitary adenylate cyclase-activating peptide (PACAP), and it is strongly expressed in dorsal paired medial (DPM) neurons. DPM neurons ramify throughout the mushroom bodies in the adult fly brain, and they are required for stable memory. Here, we show that DPM neuron output is only required during the consolidation phase for middle-term odor memory and is dispensable during acquisition and recall. However, we found that DPM neuron output is required during acquisition of a benzaldehyde odor memory. We show that flies sense benzaldehyde by the classical olfactory and a noncanonical route. These results suggest that DPM neurons are required to consolidate memory and are differently involved in memory of a volatile that requires multisensory integration.

An Identified Neuron Mediates the Unconditioned Stimulus in Associative Olfactory Learning in Honeybees

M Hammer — 2008-07-30T12:55:09-00:00

Nature, Vol. 366, No. 6450. (1993), 59-63.

DURING classical conditioning, animals learn to associate a neutral stimulus with a meaningful, or unconditioned, stimulus. The unconditioned stimulus is essential for forming associations, and modifications in the processing of the unconditioned stimulus are thought to underlie more complex learning forms1-4. Information on the neuronal representation of the unconditioned stimulus is therefore required for understanding both basic and higher-order features of conditioning. In honeybees, conditioning of the proboscis extension reflex occurs after a single pairing of an odour (conditioned stimulus) with food (unconditioned stimulus)5,6 and shows several higher-order features of conditioning6-8. I report here the identification of an interneuron that mediates the unconditioned stimulus in this associative learning. Its physiology is also compatible with a function in complex forms of associative learning. This neuron provides the first direct access to the cellular mechanisms underlying the reinforcing properties of the unconditioned stimulus pathway.

An engram found? Evaluating the evidence from fruit flies

B Gerber — 2008-07-30T12:54:51-00:00

Curr Opin Neurobiol, Vol. 14, No. 6. (2004), 737-44.

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.

Operant conditioning of antennal muscle activity in the honey bee (Apis mellifera L.)

J Erber — 2008-07-30T12:54:22-00:00

J. Comp. Physiol. A-Sens. Neural Behav. Physiol., Vol. 186, No. 6. (2000), 557-565.

Antennal movements of the honey bee can be conditioned operantly under laboratory conditions. Using this behavioural paradigm we have developed a preparation in which the activity of a single antennal muscle has been operantly conditioned. This muscle, the fast flagellum flexor muscle, is innervated by an identified motoneuron whose action potentials correlate 1:1 with the muscle potentials. The activity of the fast flagellum flexor muscle was recorded extracellularly from the scapus of the antenna. The animal was rewarded with a drop of sucrose solution whenever the muscle activity exceeded a defined reward threshold. The reward threshold was one standard deviation above the mean spontaneous frequency prior to conditioning. After ten conditioning trials, the frequency of the muscle potentials had increased significantly compared to the spontaneous frequency. The conditioned changes of frequency were observed for 30 min after conditioning. No significant changes of the frequency were found in the yoke control group. The firing pattern of the muscle potentials did not change significantly after conditioning or feeding. Fixing the antennal joints reduces or abolishes associative operant conditioning. The conditioned changes of the frequency of muscle potentials in the freely moving antenna are directly comparable to the behavioural changes during operant conditioning.

Operant conditioning in invertebrates

B Brembs — 2008-07-30T12:53:40-00:00

Current Opinion in Neurobiology, Vol. 13, No. 6. (2003), 710-717.

Learning to anticipate future events on the basis of past experience with the consequences of one's own behavior (operant conditioning) is a simple form of learning that humans share with most other animals, including invertebrates. Three model organisms have recently made significant contributions towards a mechanistic model of operant conditioning, because of their special technical advantages. Research using the fruit fly Drosophila melanogaster implicated the ignorant gene in operant conditioning in the heat-box, research on the sea slug Aplysia californica contributed a cellular mechanism of behavior selection at a convergence point of operant behavior and reward, and research on the pond snail Lymnaea stagnalis elucidated the role of a behavior-initiating neuron in operant conditioning. These insights demonstrate the usefulness of a variety of invertebrate model systems to complement and stimulate research in vertebrates.

Dopamine-Mushroom Body Circuit Regulates Saliency-Based Decision-Making in Drosophila

Ke Zhang — 2007-06-29T08:23:23-00:00

Science, Vol. 316, No. 5833. (29 June 2007), pp. 1901-1904.

Drosophila melanogaster can make appropriate choices among alternative flight options on the basis of the relative salience of competing visual cues. We show that this choice behavior consists of early and late phases; the former requires activation of the dopaminergic system and mushroom bodies, whereas the latter is independent of these activities. Immunohistological analysis showed that mushroom bodies are densely innervated by dopaminergic axons. Thus, the circuit from the dopamine system to mushroom bodies is crucial for choice behavior in Drosophila. 10.1126/science.1137357