Single-cell and network voltage imaging in acute brain slices: an updated guideline

Membrane potential (or voltage) imaging in acute brain slices is widely used in fundamental and applied neuroscience even in an age characterised by the surge of in-vivo recording. This optical method remarkably increased its ability in providing key information both at the level of single cell and at the level of populations and networks. But, more importantly, technical progresses occurred in the last two decades enlarged the potential pool of voltage imaging users from relatively few specialists to scientists in many fields including those working in industry. This review aims at offering an updated guideline for anyone wishing to perform voltage imaging in brain slices. We analyse the technical and practical aspects to consider in the choice between using an organic voltage sensitive dye (VSD) or a genetically encoded voltage indicator (GEVI). We then examine advantages and disadvantages of using the straightforward approach of wide-field illumination, versus other methods providing higher spatial resolution and optical sectioning. Other choices are analysed in particular for users adopting VSDs who are confronted with the decision of recording from single neurons or from neuronal populations. The review is concluded by exploring the prospective of applications in the near future.