Even under the most humdrum conditions — “normal lighting; no sensory cues; they're not hungry”, says Zlatic — her fly larvae can be made to perform 30 different actions, including retracting or turning their heads, or rolling. The actions are generated by a brain comprising just 15,000 neurons. That is nothing compared with the 86 billion in a human brain, which is one of the reasons Zlatic and her teammates like the maggots so much.
“At the moment, really, the Drosophila larva is the sweet spot,” says Albert Cardona, Zlatic's collaborator and husband, who is also at Janelia. “If you can get the wiring diagram, you have an excellent starting point for seeing how the central nervous system works.”
Zlatic and Cardona lead two of the dozens of groups around the world that are generating detailed wiring diagrams for brains of model organisms. New tools and techniques for slicing up brains and tracing their connections have hastened progress over the past few years. And the resulting neural-network diagrams are yielding surprises — showing, for example, that a brain can use one network in multiple ways to create the same behaviours.
But understanding even the simplest of circuits — orders of magnitude smaller than those in Zlatic's maggots — presents a host of challenges. Circuits vary in layout and function from animal to animal. The systems have redundancy that makes it difficult to pin one function to one circuit. Plus, wiring alone doesn't fully explain how circuits generate behaviours; other factors, such as neurochemicals, have to be considered. “I try to avoid using the word 'understand',” says Florian Engert, who is putting together an atlas of the zebrafish brain at Harvard University in Cambridge, Massachusetts. “What do you even mean when you say you understand how something works? If you map it out, you haven't really understood anything.”
Friday, August 11, 2017
A long, long way to go
Here's an article in Nature that suggests that those science fiction stories where the brain is scanned in 20 minutes and then the mind it hosts is uploaded into a computer, or another person, are just a tad unrealistic.