This is a fascinating paper that represents a significant technical advance in our possibilities of performing in vivo studies of brain activity in insects. For the first time, we can observe brain activity in vivo in flies, without the necessity of exciting a dye molecule with a specific wavelength to produce fluorescence. The animal will exhibit such fluorescence by itself, simply when the appropriate brain structures or sets of neurons are activated. This is simply a tour de force that, from the technical point of view, deserves highest attention.

However, one of the most exciting points of the papers remain unclear. The secondary delayed peak of intracellular Ca2+ release occurring 15 min after nicotine application is a surprising finding that could have dramatic functional consequences for the olfactory system. Why, when such a system is stimulated and responds consequently, is it possible to see 15 min (!) later a secondary excitation peak?It is a bit deceiving that no functional studies are presented here to understand the specific role of this secondary activation . Studies related to olfactory discrimination and generalization and/or olfactory memory dynamics should be necessary to address the fucntional role of this peak.

This being said, this unanswered point does rest merit to this important work, which constitutes a significant technical advance in studies on insect brain activity.

Martin Giurfa
CNRS - University of Tou