Development of novel optical tools to investigate ensemble dynamics of large-scale neural populations within freely behaving rodents

A longstanding goal in neuroscience is to unravel the neural basis of perception, memory formation and behaviors. To address this goal, it can be useful to manipulate and record neuronal activity with cellular precision while the animal (here, a rodent) is performing specific behavioral tasks. Such experiments can be performed with optical methods, using photostimulation of optogenetic actuators and fluorescence imaging of calcium reporters. To apply optical methods to freely-behaving mice, two approaches have been followed: a microscope can be fully miniaturized and placed on the rodent head, or an image guide can be used as a relay between a regular-size custom-made microscope and the animal, which allows us to partly overcome miniaturization constraints.

Using this second strategy, we have developped a fiberscope for fast fluorescence imaging with optical sectioning, using multipoint- and line-scanning confocal imaging [1]. For both imaging modalities, the illumination beam is shaped by intensity modulation with a digital micro-mirror device, providing high adaptability to the sample and imaging conditions. Using this device, we demonstrated fast (>100 Hz) fluorescence imaging of blood flow and neuronal activity in the brain of freely-behaving mice, with reduced out-of-focus background compared with widefield imaging. In particular, we have been able to simultaneously register neuronal activity of >100 cells at 100 Hz in the hippocampus of freely behaving mice [2]. We are currently working on improving the fluorescence signal and background rejection by developping novel high NA micro-objectives, and on coupling the fiberscope with electrophysiological recordings.

[1] Dussaux et al, Scientific Reports 8, 16262 (2018).
[2] Dussaux et al, in preparation