Susannah Hannaford

I am a neurobiologist. I study nerve cells, the circuits into which these cells are organized, and the behavior they mediate. My particular area of specialization is sensory physiology. This area of neuroscience focuses on how animals detect changes in their environment and process this information in their brains. The problem is complex. Animals are bombarded with information; their environment is filled with light and sound waves, with electromagnetic energy, with mechanical vibrations, and with chemicals. How can an animal sort through this complexity to detect the important features -- potential mates, predators and food? Over the past 15 years I have a variety of insect behaviors ranging from how flies "taste" their environment with their feet and wings, how male moths find conspecific mates and avoid females of other closely-related genera, and how insects detect forces on their wings and use this sensory information to refine their flight.

Recently I have started looking at another insect system in collaboration with Robin Foster (Dept. of Psychology). Robin has spent many years studying the division of labor in bumblebees. Bumblebees, like other social insects, have a social structure. A queen establishes a nest and then lays eggs which will become worker bees. Worker bees themselves have a number of possible jobs. Some of the bees stay in the nest and are involved in nest defense, brood care, egg-cell construction and egg laying. Other bees are specialized for foraging &endash; they leave the nest, collect nectar and pollen, and bring it back to feed the other nest members. We would expect that the differences in behavioral roles would be reflected in some aspect of the sensory biology and brains of the bees. In particular, the bees that forage for food sources might have specializations in the part of the brain that "learn" and "remember" foraging sites.

Studies in other insect systems have revealed that a particular portion of the insect brain, the mushroom bodies, is involved in learning and memory. This brain region receives input from several different sensory modalities &endash; information from the antennae (smell), mouthparts (taste), eyes (vision), and body (touch) all converge in the mushroom bodies. This is what we would expect in a part of the brain that is involved in complex tasks such as learning and memory. Moreover, a number of studies have shown that the size of the mushroom bodies is related to experience and to an insect's ability to learn and remember (for details, see references below). Robin and I are now interested in extending this work to bumblebees and looking at the structure and size of the mushroom bodies.

The behavioral aspects of the study will be carried out in Robin Foster's lab in the Psychology Department. Because the colonies are established in the spring and die back in the fall, students wishing to work on behavioral aspects of the project would have to make a commitment to work in the summer months.

Work in my lab will focus on looking at the brains themselves. Insect brains are very small, and it is not possible to see differences in brain structure without special methods. Our approach has been to dissect out the brains from the bumblebees, place them in a fixative solution (this crosslinks proteins, stiffening the tissue and preventing degradation), and then sectioning them. To date we have been making frozen sections of the brains. These sections are 20 microns thick. Once the brains are sectioned, we can look at them with a microscope, identify the various brain regions, and even use computer programs to measure the size of the regions in different bees. I am also interested in examining the bee brains at an even finer level of detail. Two possible approaches are using plastic sections (2 to 4 microns in thickness) and ultrathin sections (requiring electron microscopy). Regardess of the method used, the ultimate goal is to determine if differences in the behavior of the animal are correlated with specific differences in the brain structure.

Selected References

Background

Menzel R. and A. Mercer eds (1987) Neurobiology and Behavior of Honeybees. Springer-Verlag. Good overview of honeybee neurobiology.

Robinson, G. E. 1992. Regulation of division of labor in insect socieites. Ann. Rev. Entomol. 37, 637-665. Reviews the social structures and division of labor in a number of insects.

Studies on mushroom body structure in honeybee brains

Fahrbach, S.E., D. Moore, E.A. Capaldi, S.M. Farris and G.E. Robinson 1998. Experience-expectant plasticity in the mushroom bodies of the honey bee.  Learning Memory 5, 115-123.

Farris, S.M., G.E. Robinson and S.E. Fahrbach 2001. Experience- and age-related outgrowth of intrinsic neurons in the mushroom bodies of the adult worker honey bee.  Journal of Neuroscience 21: 6395-6404.