Neuronal control of complex behavior; multimodal information processing and brain plasticity

Sensory-motor reflexes. The mandibles are the most important tools of most insects and they are used for many different tasks requiring a wide range of force output and movement velocities (biting, cutting, defense, seed cracking, digging, grooming, brood care, etc.). In biting insects (e.g. ants and wasps), jaws are powered by particularly large muscles. Using electrophysiology, force- and movement measurements and anatomical methods, we investigate how the relatively small number of motor neurons that control the jaw muscles can generate the wide range of movements, among which are some of the fastest reflexes known (in trap-jaw ants).

Brain and behavior. Most insects and all ants rely on olfaction and tactile cues for communication and orientation. Wasps and bees, and some ants are expressively visual animals that use their keen sight to navigate by visual landmarks, the position of the sun or moon, or the polarization pattern of the skylight. They rely on vision to find flowers, nests, or lekking points, to catch prey (wasps and ants) and even for individual 'face' recognition (some paper wasps).By comparing the brains of insects that rely on different sensory cues and show very different behavior we try to get insights into the function of particular brain structures. The brains of Hymenoptera comprise prominent antennal lobes that process odor information, and the visual brain centers are large in bees and wasps, but small small in most ants. The antennal and optic lobes assess significant stimulus features (such as odor quality and strength, light color, pattern, movement). Other brain compartments concatenate these features and determine their significance with regard to temporal and spatial conditions and previous experience to give rise to complex behavior. The so-called mushroom bodies are involved in the generation of such complex decision-making. These central brain structures process multimodal information and supposedly control orientation, complex movement and learning and memory. The mushroom bodies are particularly large in ants and bees, suggesting a correlation with their rich behavioral repertoire. We analyze the brains and nerve cells of different species and castes to quantify differences in their brain design. These data are compared to the behavioral performance of the respective species in quantitative laboratory tests (walking, orientation, learning paradigms). We are particularly interested in the structure and function of neurons associated with the mushroom bodies and try to find out how visual and olfactory information is represented in and processed by mushroom body neurons. Behavioral deficits resulting from focused brain ablations help to determine the functional significance of certain brain sub-compartments and groups of neurons.

Neuronal and behavioral plasticity. In addition to their overall complex behavior, social insect colonies are based on caste systems. Besides reproductive males and females, the majority of individuals in the colonies are workers (e.g. nurses, foragers, soldiers). In many ant species, worker castes may differ morphologically (e.g. body size). Although genetically almost identical, these workers show cast-specific responses when confronted with particular stimuli. Moreover, their individual behavior may change over time as virgins become queens or as nurses become foragers. We assess their changing behavior and learning abilities and analyze concomitant changes in the neuronal substrate, particularly in the mushroom bodies. Neuronal changes associated with such behavioral transitions are also examined in deprivation experiments in which the importance of sensory experience for the development of the brain and of normal behavior is assessed. Similar neuronal changes occur in vertebrates as they become more experienced, but it is easier to examine such effects in social insects.

Selected Recent Publications

Mares S, Ash L, Gronenberg W. Apr 2005. Brain Allometry in Bumblebee and Honey Bee Workers. Brain Behav Evol, 66:50-61

Ramon F, Gronenberg W. Mar 2005. Electrical potentials indicate stimulus expectancy in the brains of ants and bees. Cell Mol Neurobiol, 25:313-27

Ehmer B, Gronenberg W. Feb 2004. Mushroom body volumes and visual interneurons in ants: comparison between sexes and castes. J Comp Neurol, 469:198-213

Gronenberg W, Lopez-Riquelme GO. Jan 2004. Multisensory convergence in the mushroom bodies of ants and bees. Acta Biol Hung, 55:31-7

Ehmer B, Gronenberg W. Sep 2002. Segregation of visual input to the mushroom bodies in the honeybee (Apis mellifera). J Comp Neurol, 451:362-73

Paul J, Gronenberg W. Feb 2002. Motor control of the mandible closer muscle in ants. J Insect Physiol, 48:255-267

Julian GE, Gronenberg W. Jan 2002. Reduction of brain volume correlates with behavioral changes in queen ants. Brain Behav Evol, 60:152-64

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