By modifying genes to light up in one of three fluorescent colors during neural signaling, neuroscientists at Northwestern University have managed to (retrospectively) read the minds of fruit flies up to three hours after an event. This new technique could help in efforts to map the circuits within fruit fly brains, and that in turn might provide insights into the workings of the human brain.

The researchers developed their technique so that they could study the brain activity of fruit flies as they perform complex behavior. They adapted the gene for a green fluorescent protein found in some species of jellyfish to the purpose. They applied green, blue, and yellow fluorescent molecules to the flies' neural connections for the olfactory (smell), visual, and thermosensory systems – half of each molecule tied to each end of a synapse (the bridge across which information flows between two neurons).

The flies then went through various sensory experiences, smelling bananas, light or heat exposure, and so on. Afterwards the scientists could study the fluorescent signals (which persisted) under a microscope to see how the fly brains responded.

The patterns of activity evident in the signals differed according to both the type and duration of the event as well as on other details such as whether the fly smelled banana or jasmine.

This has great implications for the study of fruit fly brain circuitry, as the labeling technique allows neuroscientists to identify the individual synapses involved in complex behavior such as avoiding heat or locating food.

This kind of wire diagram mapping is one of the holy grails of modern neuroscience, and any insights gained here in fruit fly studies may aid in making sense of the far more complicated brains of humans and other mammals (to give you an idea of the differing scale of human versus fruit fly brain, fruit flies have around 100,000 neurons and 10 million synapses whereas humans have on the order of a hundred billion neurons and hundred trillion synapses).

The study is described in the journal Nature Communications.