Tiny Fly Brains Are High Speed Motion Computers
Posted on July 14, 2010
Tiny fly brains can process visual movements in only fractions of a second. Flies can process a vast amount of information about motion and movement in their environment in real time. This is a feat that no computer, and certainly none the size of a fly's brain, can match. Scientists at the Max Planck Institute of Neurobiology are attempting to decode the underlying mechanisms of the fly's rapid motion vision.
Dierk Reiff from the Max Planck Institute of Neurobiology in Martinsried says one sixth of a cubic millimetre of fly rain matter contains more than 100,000 nerve cells - each of which has multiple connections to its neighbouring cells. Neurobiologists in Martinsried have managed to single out the reaction of a certain cell to any particular movement stimulus.
"We had to find some way of observing the activity of these tiny nerve cells without electrodes", Dierk Reiff explains one of the challenges that faced the scientists. The scientists used the fruit fly Drosophila melanogaster and some of the most up-to-date genetic methods available. They succeeded in introducing the indicator molecule TN-XXL into individual nerve cells. By altering its fluorescent properties, TN-XXL indicates the activity of nerve cells.
To examine how the brains of fruit flies process motion, the neurobiologists presented the insects with moving stripe patterns on a light-diode screen. The nerve cells in the flies' brains react to these LED light impulses by becoming active, thus causing the luminance of the indicator molecules to change.
The scientists observed the activity of cells known as L2-cells, which receive information from the photoreceptors of the eye. The photoreceptors react when the light intensity increases or decreases. The reaction of the L2-cells is similar in that part of the cell where the information from the photoreceptor is picked up. However, the neurobiologists discovered that the L2-cell transforms these data and in particular, that it relays information only about the reduction in light intensity to the following nerve cells. The latter then calculate the direction of motion and pass this information on to the flight control system.
Now that the first step has been taken, the scientists intend to examine - cell by cell - the motion detection circuitry in the fly brain to explain how it computes motion information at the cellular level.