The scope of optogenetic studies

Optogenetics is extremely young, the first experiment—triggering neuronal action potentials using light—was done in 2002. Since then it has been used in a variety of animal models including the nematode Caenorhabditis elegans, the fruit fly Drosophila, zebra fish, mice, and primates for three broad classes of investigation:

- Tracing of neuronal connections. This has shown, for example, that neocortical pyramidal cell dendritic trees are segregated into functional domains according to input with local, ascending, and descending axons going to specific domains.

- Neural network activity. This has revealed that brain circuits exist for behaviors an animal would not normally exhibit, such as male courtship display in a female.

- Neural mechanisms of sensation, reward, and cognition.

Optogenetics is being used in combination with other techniques, such as extracellular recording from awake behaving animals and with fMRI (in this case to establish precisely what cellular events were required to explain the fMRI signal).