New generations of portable microscopes for calcium imaging enable observation of simultaneous activity in hundreds-to-thousands of distinguishable neurons while animals perform experimental tasks, allowing researchers to identify the underlying neural dynamics and computational algorithms, goals that would be out of reach if cells were recorded one by one or a few at the time. Among these new miniature microscopy techniques, the miniature two-photon microscopes -2P miniscopes- is of particular interest for applications that require high anatomical resolution and the ability to distinguish between recorded cells based on their genetic expression, somatic location, or axonal projection pattern. Early versions of 2P miniscopes did not catch on, however, because they lacked the capacity to image sensitive calcium indicators such as GCaMP6, because their scanning speed was slow, because the miniscopes were heavy and difficult to carry for rodents, or because optical cables were stiff and inflexible. These constraints motivated the development of a new generation of 2P miniscopes with benchtop-comparable 2P resolution, fast speed, Z-scanning capability, and a large field of view (FOV). However, while these 2P miniscopes represented major advances in imaging quality, their applicability in tasks that require movement is still limited, due to heavyweight, stiff optical cable connections, low cell yield, and high system complexity. As of today, calcium imaging technology is thus not suitable for recording activity at the scale of hundreds to thousands of neurons, and at the high spatial and temporal resolution, during spatially dispersed behavior in freely-moving animals. Therefore, the aim of the ANAT-MEC project is to develop a new generation of 2P miniscope that enables the study of neural activity, at high sampling rates and with high spatial resolution, in thousands of individually identifiable cells in cortices with different architectures and locations, while mice move freely in the environment. The new 2P miniscope developed in this project will open many new doors to the neuroscientists to image large-scale cellular and subcellular structures in actively moving animals and will bring us closer than ever before to understanding the fundamental principles underlying complex behaviors.
The overall objectives include 1) developing a new 2P miniscope that enables the study of neural activity, at high sampling rates and with high spatial resolution, while mice move freely in the environment, 2) demonstrating the feasibility of large-scale imaging through prisms implanted along the elongated dorsoventrally surface of MEC to study the anatomical organization of grid cells, and 3) providing the open-source materials for building this 2P miniscope system so it can be easily duplicated in any biology lab with basic optics and electronic experience.
