“Conceptually, anatomy has always been single case studies,” says Heisenberg. A few years ago he saw an opportunity to change this situation. Scientists now had the computing power and confocal microscopy expertise needed to compare multiple, entire fly brains. When Heisenberg did so, he found that the brain images could be superimposed with only a 15% standard deviation, thus yielding the standard brain.This was the standard brain for the Canton-S fly strain, which has been wandering around food vials for over 1,000 generations. But when Heisenberg made a standard brain for the more recently tamed Lindelbach strain, he found that two brain regions implicated in flight control were 10–15% larger in Lindelbach than those in Canton-S, whereas a brain region used in walking control was 10% smaller. Apparently, fly researchers have been studying an organism that is better adapted to sauntering than soaring.
Now that the standard brain has been established, others can contribute to it by using a fairly standard computer set-up. Brain whole-mounts and imaging tend to be fast, but a single brain can take 2 days to analyze because of the time needed for manual outlining and assigning of each brain region. The two days should be reduced to several hours by a program—still under development—that will do most of the outlining automatically.
Although the protocol may be too cumbersome for large scale mutant screens, Heisenberg believes that numerous labs can contribute expression patterns to the model. “Standardization of these gene expression patterns with respect to each other will help us make sense of them,” he says. “We need a link between the gene level and the anatomic level.” ▪