Scientists from the Max Planck Institute of Neurobiology in Martinsried have developed a method that allows them to identify nerve cells involved in a specific motor command. For the first time, it is now possible to evoke behaviour of a small fish by artificially activating just a handful of neurons. Understanding the core components of a neural circuit is a key step for deciphering the complex code underlying even elementary brain functions.
Recent years have seen much progress in understanding of the brain’s structure and function. Advances in microscopy and functional imaging enable researchers to monitor the activity of neuronal populations, while an animal perceives sensory stimuli or generates specific behaviours. However, these studies often cannot distinguish cause from consequence of the observed changes in activity. Using the method of optogenetics, scientists can find out which neurons are essential for the chain of events that ultimately lead to behaviour, and which neurons may serve other tasks or are merely by-standers. A particular challenge for this field of research is the staggering degree of "interconnectedness" of neuronal networks. Activating even a single neuron may send ripples through a large part of the nervous system. The new study from Herwig Baier and his team at the Max Planck Institute of Neurobiology has removed both obstacles in one sweep: it is now possible to pinpoint cause and effect to the cellular components of neural circuitry while simultaneously watching how activity propagates through the entire brain network and evokes behaviour.
The Martinsried scientists developed a workflow allowing the 3D photo-stimulation of multiple targeted neurons while, at the same time, imaging network activity in the brain of a zebrafish larva. “The zebrafish with its small, translucent brain is ideal for our new method”, explains Marco dal Maschio, one of the two lead authors of the publication describing the technique.