Fruit Flies Unravel Brain Mysteries

Behavioural experiments

These visual experiments are uncovering the pathways that flies use to see the world around them. In parallel, other scientists are conducting behavioural experiments that show how a fly's visual pathways relate to its motivation and choices.

The Drosophila flight simulator (pictured above) is ideal for analysing how the brain of the fly is optimised for processing visual information from its environment. Most animals use previous experience to choose different behaviours by assessing the advantages and disadvantages of conflicting cues. The neural mechanism of this process, however, is largely unknown.

In the flight simulator, researchers can train the fruit fly to follow certain visual patterns, with the help of a punishment such as heat. The fly, which is tethered, is presented with two conflicting cues (pictured below) with one of the patterns causing pain - in the form of heat - when it enters the fly's field of view. Following this training, the researcher examines which direction the Drosophila tries to flee in.

Normal "wild-type" flies learn to avoid the heat punishment and fly away from the cue that's associated with pain. But if you perform the experiment with a mutant fly that has a part of its brain controlling choice behaviour that does not work effectively, then it will behave differently. For example, the fly may not be able to make the correct choice and fly in the direction of the heat. From such results, scientists can deduce what this brain element has to do with choice behaviour.

With this method, researchers have been able to determine what different areas of the fly's brain are responsible for. They've uncovered, for example, evidence that the area of the brain called the mushroom bodies have a lot to do with choice behaviour. And so they are gradually are building up a much better understanding of the complexities of the neural pathways within the brain, and their function.

But much is still not understood about the brain, its complexities and its interactions. Experiments like this are enabling scientists to better understand how neurones work individually and collectively. Because of the similarity in the genomes between the fruit fly and us, some of this research on Drosophila brains can be applied to the human system.

The emergence of this new genetic information should enable more advanced and accelerated research on diseases and drugs to combat genetic diseases.

Future work

The importance of Drosophila is clear, and it has a major role in furthering our understanding of the brain. Due to the unique nature of the genetic system of the Drosophila and the advanced techniques now available to researchers, even the most detailed pathways can be uncovered and their interactions unravelled.

The complete sequencing of the Drosophila genome has provided mounting evidence for the similarity between Drosophila and human genes that control genetic disorders. The humble fruit fly has now become an indispensable tool for studying human diseases, as well as a model to test for drugs and pharmaceuticals against human diseases and complex behavioural processes.

In the future this research may be applied to the development of therapies to treat human disease pathologies - but for now, there is still much to be done.

For more information

Dr Mikko Juusola's research on fruit fly eyes
http://www.shef.ac.uk:80/bms/research/juusola/research.html

Professor Roger Hardie's research into the fly's visual mechanism
http://www.neuroscience.cam.ac.uk/directory/profile.php?rch14

References

Tang, S. & Guo, A., Science, Choice Behaviour of Drosophila Facing Contradictory Visual Cues Vol 294 P.1543-1547 (2001).

Chan, H.Y.E. & Bonini, N.M., Nature, Drosophila models of human neurodegenerative disease Vol 7, No. 11, P.1075-1080 (2000).

Hardie, R.C. & Raghu, P., Nature, Visual transduction in Drosophila Vol 413, P.186-193 (2001).

Adams, M.D., et al, Science, The Genome Sequence of Drosophila melanogaster Vol 287 no. 5461, P.2185-2195 (2000).

Reiter, L.T., et al, Genome Research, A Systematic Analysis of Human Disease-Associated Gene Sequences in Drosophila melanogaster Vol 11, P.1114-1125 (2001).

Juusola, M. & Hardie, R., J. Gen. Physiol, Light Adaptation in Drosophila Photoreceptors: I. Response Dynamics and Signalling Efficiency at 25°C Vol 117, P.3-25 (2001).

Zheng, L. et al, J. Gen. Physiol, Feedback Network Controls Photoreceptor Output at the Layer of First Visual Synapses in Drosophila Vol 127, no. 5, P.495-510 (2006).

Colley, N. J, University of Wisconsin Department of Ophthalmology and Visual Sciences © 2006, http://www.ophth.wisc.edu/research/reslion.htm

Joshi, A. et al, Current science, Mutants dissecting development and behaviour in Drosophila Vol. 89, no. 2, P.341-352 (2005).