Using the fruitfly (pictured) as a model to investigate human traits such as attention span might seem odd. But the power of Drosophila genetics, together with previous studies pointing to sophisticated behavioural responses in this organism, in fact makes it an ideal choice for studying how our minds wander.

Bruno van Swinderen suspended flies in a cylindrical arena with rotating walls on which one of two simple visual stimuli was displayed (B. van Swinderen Science 315, 1590–1593; 2007). He found that, each time the stimuli were switched, the fly's local field potential (LFP) activity — a measure of the total electrical activity at the junctions between neurons — increased. When the same object was displayed on both sides of the rotating cylinder there was no increased LFP response when it appeared anew. This ruled out the possibility that the elevated LFP response to a second object was simply due to a startle reflex.

Credit: PHOTOTAKE/PHOTOLIBRARY.COM

When alternating the two visual stimuli, van Swinderen found that an interval of at least 50 seconds was required since the flies last saw the object for that stimulus to regain its novelty value, as measured by increased LFP activity. This response lasted an average of 9 seconds before the object lost its salience once more.

The author next performed these tests on two fly mutants — dunce and rutabaga. The proteins encoded by these genes normally alter levels of the same molecule, cAMP, and the mutants show similar defects in short-term memory. Van Swinderen found that the LFP activity in the brains of these mutants did not fluctuate appropriately in response to novel visual stimuli.

Might it simply be that the general responsiveness to visual cues is defective in these mutants? Surprisingly, the answer seems to be no. Van Swinderen found not only that visual responsiveness was unaffected, but also that, following an initial delay, it was in fact far higher in the dunce mutants than in normal flies. Further experiments confirmed that although the mutant flies responded normally to visual stimuli, they were defective in identifying a new stimulus.

These results highlight the importance of the ability not just to pay attention, but also to divert it when necessary. The excessive responsiveness of the mutant flies to one visual stimulus seems to compromise short-term-memory activities such as shifting attention, or simultaneously paying attention, to another object. When the product of the dunce gene, the enzyme cAMP phosphodiesterase, was expressed throughout brain development, the attention defects associated with the mutation were overcome. This indicates that the developmental activity of cAMP is crucial for characteristics resembling attention in adult flies. Further analysis of both gene and enzyme should improve our understanding of what it takes to grab flies' — and perhaps humans' — attention.