In the first part of our ERC grant period we have designed, built, and amended such a 3D microscope, which may operate with multiple independent laser lines to record and simultaneously stimulate neurons in 3D in large cortical volumes. To reveal what the cellular networks in the visual cortex are exactly doing when computing the features of the surrounding world, it is vital that we image not only small regions but the entire V1 and also secondary visual areas in the entire depth of the cortex with high speed. To achieve high scanning depths and to extend z-scanning range and provide simultaneous photo-stimulation we also built a virus laboratory which provides us means to produce and deliver genetically coded sensors and opsins in many combinations.
We have also designed and produced a large objective (a mesoscopic objective) to image not only the entire depth of the cortex, but also to provide large field-of-view simultaneously. Currently we can provide 3300 × 3000 × 1000 µm3 scanning volume for fast 3D imaging. These are the prerequisites of revealing what happens in the brain when we dwell in the visual world.
We have built and still are working on a virtual reality environment which makes possible a reality-like visual stimulation under the very complex microscope, so we can study the activity of the visual cortex whilst the mouse is engaged in a given visual task with different visual cues.
We have also started recording activity of neuronal populations with the fast 3D acousto-optical microscope in mice navigating in virtual reality and revealed new principles driving the processes in visual computations. We have detected that temporal components of the visual information are represented in the V1 region of the cortex in overlapping spatiotemporal clusters of neurons.
Our eventual goal is to better characterize the coding and relevance of these novel spatio-temporal clusters in cortical networks activity in response to the visual features of the environment when the animal is navigating in it, and then replicate them by stimulating the neural tissue directly, skipping the information from the eyes but providing similar subjective perception for the animal.
We have already performed many recordings in the visual cortex of the animals running in virtual mazes. We have realized that the network activities have a precise temporal build up which have not been explored so far in the related literature. This temporal build up and changes of it may be described by novel mathematical tools. This insight is an important step towards solving the practical question of how to stimulate the network properly, how to activate clusters of neurons to elicit similar behavior than what would be initiated by real sight.
Our future plans are to find the appropriate so called “opsins” with which it will be possible to actually do the stimulation in a cell-type specific, temporally and spatially very precise manner (the opsins we work with currently have some limitations in these respects); finish the development of a flexible virtual reality system; complete the analysis of the principles guiding visual cortical network operations; and eventually test our results by guiding animal through the virtual maze by stimulating directly their brains.
