Showing papers by "Martin Heisenberg published in 1999"

Context generalization in Drosophila visual learning requires the mushroom bodies

Abstract: 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 possible1. 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 (context2). 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 simulator3,4, and show that memory retrieval is, indeed, partially context-independent. Moreover, we show that the mushroom bodies, which are required for olfactory5,6,7 but not visual or tactile learning8, 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.

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.

Temporal pattern of locomotor activity in Drosophila melanogaster.

Abstract: The temporal pattern of locomotor activity of single Drosophila melanogaster flies freely walking in small tubes is described. Locomotor activity monitored by a light gate has a characteristic time-course that depends upon age and the environmental conditions. Several methods are applied to assess the complexity of the temporal pattern. The pattern varies according to sex, genotype, age and environmental conditions (food; light). Activity occurs clustered in bouts. The intrinsic bout structure is quantified by four parameters: number of light gate passages (counts) per bout, duration of a bout, pause between two successive bouts and mean bout period. In addition, the distribution of the periods between light-gate crossings (inter-count intervals) as function of inter-count interval duration reveals a power law, suggesting that the overall distribution of episodes of activity and inactivity has a fractal structure. In the dark without food, the fractal dimension which represents a measure of the complexity of the pattern is sex, genotype and age specific. Fractality is abolished by additional sensory stimulation (food; light). We propose that time-course, bout structure and fractal dimension of the temporal pattern of locomotor activity describe different aspects of the fly's central pattern generator for locomotion and its motivational control.