Lecoq, J. et al. Nat. Neurosci. 17, 1825–1829 (2014).

To understand the functional relationship between different brain areas, researchers must obtain information on the electrical activity of neurons in these areas at the same time. Lecoq et al. developed a two-photon microscope with two arms, which the researchers can independently direct to the areas of interest. These microscope arms harbor miniaturized objectives, and a mirror diverts the light path for one of the objectives to allow even closer juxtaposition of the areas to be analyzed. With this microscope, Lecoq et al. performed simultaneous calcium imaging in awake, head-fixed mice in brain regions that were about 1 millimeter apart. They discovered that the activity in the lateromedial visual area depends on the activity of the primary visual cortex.