A wireless miniScope for deep brain imaging in freely moving mice

Abstract

Background: The increasing interest in the study of neuronal activities at the microcircuit level is motivating neuroscientists and engineers to push the limits in developing miniature in vivo imaging systems. This inter-disciplinary effort led to an increasingly widespread use of wearable miniature microscopes, constantly improving in size, cost, spatial and temporal resolutions, and signal to noise ratio.

New method: Here we developed a miniature wireless fluorescence microscope (miniScope) that allows recording of brain neural activities at single cell resolution. The wireless miniScope has onboard field-programmable gate array (FPGA) and Micro SD Card storage, and is powered by a battery backpack.

Results: Using this wireless miniScope, we simultaneously recorded activities from hundreds of medium spiny neurons (MSNs) in the dorsal striatum of two freely moving mice interacting with each other in an open field, with excellent spatial and temporal resolutions.

Comparison with existing methods: Existing miniaturized microscope systems have connecting cables between the microscope sensor and the data acquisition system, consequently limiting the recording to one animal at a time. The wireless miniScope allows simultaneous recording of multiple mice in a group, and could also be applied to freely behaving small primates in the future.

Conclusion: The wireless miniScope expands the realm of possible behavioral experiments, both by minimizing the repercussions of the cable from the imaging device on the rodent's behavior and by enabling simultaneous in vivo imaging from multiple animals.

Keywords: Calcium imaging; Locomotion; Striatum; Wireless; miniScope.

Figure 1. Wireless miniScope imaging system.

A. An illustration of a mouse wearing the wireless miniScope with a battery backpack. B. An illustration of mounting of the wireless miniScope on mouse head and coupled to a GRIN lens for in vivo deep brain imaging. C. A photo of an actual wireless miniScope side by side with a Quarter. D. Overall design of wireless miniScope, scale bar 4 mm. E. System architecture overview. F. A representative standard deviation projection image of GCaMP6s fluorescence images captured by the wireless miniScope imaging system. The D2 neurons detected by the automatic cell identification algorithm are overlaid in green. G. Representative calcium transient traces from 25 representative identified D2 neurons; the red arrows mark the onset of the detected calcium transients. H. Representative mouse locomotion trajectories of two mice both wearing a wireless miniScope during a 3-minute open field session.

Figure 2. Simultaneous imaging of two mice using wireless miniScope in open field test.

A. Rasterplot of the normalized calcium traces (top) and time plot of the average population neural activity and locomotion velocity of the mouse (bottom). Both population activities of D1- and D2- MSNs show clear correlation with locomotor activity. B. Neuronal map of the two mice; color code indicates the average correlation coefficient between each neuron and the mouse locomotor speed. C. Distribution of the average correlation coefficient between neural activity and mouse speed, compared against the average correlation coefficient for calcium traces randomly shuffled 1000 times (gray bars). D. Average neuronal activity as a function of mouse speed for all neurons (left), some neurons are negatively correlated with speed (middle), and some neurons are positively correlated with speed (right). The spatial location of these neurons for the D1 (left map) and D2 (right map) mouse are shown in the inset maps (scale bar 100 μm).