Throughout life, new neurons are added to the brain. Just like people arriving late to a cocktail party, the newbies need to figure out how to integrate with those already embroiled in conversations. The zebrafish brain, already capable of complex visual processing at larval stages, accepts new neurons throughout the fish life span. Boulanger-Weill et al. tracked the location, movement, and functional integration of single newborn neurons in developing zebrafish larvae. Following their own developmental trajectories, newborn neurons began with limited dendritic arbors, no neurotransmitter identity, and spontaneous, but not directed, activity.
Next they wondered if perhaps their methods were only capable of detecting neurogenesis in young brains, and not in the brains of adults. To see if that was the case they analyzed two post-mortem autopsy samples and looked for evidence of young neurons in another region of the brain that is known to produce new neurons into childhood. There, the authors did find rare examples of young neurons, but very few.
In research described June 26 in Nature Methods, the team, led by Rockefeller's Alipasha Vaziri, used a light microscope-based technique to capture neural activity within a volume of mouse brain tissue at unprecedented speed. The algorithm allowed them to pinpoint the signals from hundreds of individual neurons in a single recording. "Our goal is to better understand brain function by monitoring the dynamics within densely interconnected, three-dimensional networks of neurons," says Vaziri, head of the Laboratory of Neurotechnology and Biophysics. For this research, Vaziri and his colleagues engineered the animals' neurons to fluoresce; the stronger the signal, the brighter the cells shine. To capture this activity, they used a technique known as light field microscopy, in which an array of lenses generates views from a variety of perspectives.
It should not only capture much more detail than existing brain probes (the team is hoping to see "a million" neurons), but reach levels deep enough that it should shed light on how the mind processes sensory input. And that, in turn, opens the door to controlling sensory input. If technologies like the microscope lead to a way to quickly interpret neuron activity, it should be possible to craft sensors that send audiovisual data to the brain and effectively take over for any missing senses. Any breakthrough on that level is a long way off (at best) when even FlatScope exists as just a prototype, but there is some hope that blindness and deafness will eventually become things of the past.