Mapping brains of fruit fly larvae may help build similar 'atlas' for humans

Mapping behaviour of fruit fly larvae raises possibility of cracking code to how we tick

PUBLISHED : Sunday, 30 March, 2014, 4:56am
UPDATED : Sunday, 30 March, 2014, 4:56am

Researchers have identified the brain neurons that cause every behaviour that fruit fly larvae execute, raising the tantalising possibility neuroscientists will be able to construct a similar "atlas" in people.

The accomplishment is an advance towards linking the neurons that fire when people make specific movements, and possibly even when they feel certain emotions, visualise objects, hear particular melodies or think certain thoughts.

Such a human brain atlas is one goal of the US$100 million BRAIN Initiative that US President Barack Obama announced a year ago, and the fly research raises hopes it will be possible to deal with the data deluge that project will generate.

For the study, published online by the journal Science, scientists led by biologist Marta Zlatic of the Howard Hughes Medical Institute's Janelia Farm research centre in the US state of Virginia first activated a few neurons at a time in the larvae of the fruit fly drosophila, using a technique called optogenetics, in which light causes particular neurons to fire. She and her team then compiled thousands of hours of video of how 37,780 fly larvae behaved in response to each neuronal activation. Hunching and wiggling, backing up and turning continuously were all popular.

Next, using specially developed software to analyse the terabytes of data in the recordings, mathematician Carey Priebe of Johns Hopkins University identified the 29 behaviours the larvae could manage: crawling forwards or backwards, turning right or left, and the like. The result was an atlas of neurons whose activation causes any movement a fly larva is capable of. Two neurons in the bottom back of the brain, for instance, made most larvae turn, turn, and turn again.

The drosophila project was feasible not only because the larvae are capable of so few behaviours but also because their brain and nerve cord contain only 10,000 neurons. The human brain has about 86 billion to 100 billion neurons.

"It's a proof of principle," said Zlatic. "It's possible to classify neurons in terms of what decisions and actions they cause."

Eventually, such a neuron-behaviour atlas might be paired with the wiring diagram of a brain. In the case of the fly larvae, Zlatic's team identified which neurons cause which behaviours, but not which neurons were activated in between or how these neurons are connected. Doing so will require what neuroscientists call a "connectome", or the complete wiring diagram of a brain.

Neurobiologists are close to accomplishing that for the mouse brain.