Brain-wide imaging of an adult vertebrate with image transfer oblique plane microscopy

Optical imaging is a powerful tool to visualise and measure neuronal activity. However, due to the size and opacity of vertebrate brains it has until now been impossible to simultaneously image neuronal circuits at cellular resolution across the entire adult brain. This is true even for the smallest known vertebrate brain in the teleost Danionella , which is still too large for existing volumetric imaging approaches. Here we introduce image transfer oblique plane microscopy, which uses a new optical refocusing solution via a custom fibre-optical face-plate, enabling a large field-of-view of up to 4 mm3 at a volume rate of 1 Hz. We demonstrate the power of this method with the first brain-wide recording of neuronal activity in an adult vertebrate. ### Competing Interest Statement The authors have declared no competing interest.