I have been reading literature regarding Neuronal potential measurement. Conventionally, researchers use electrode-based method to measure action potential. However, as it's of high invasiveness and low throughput several optical methods such as Genetically encoded voltage indicators (GEVIs) and chemical methods such as Voltage-sensitive dyes (VSDs) are emerging. One fundamental question I came across was GEVIs indeed can be targeted to the site of interest however, there only a few chemical methods targeting specific cell type have been developed. One such recent literature is this one: https://pubs.acs.org/doi/10.1021/jacs.0c00861. I am wondering, are neuroscience researchers really interested in measuring neuronal potential at individual synapses (which is gradient) or only at the axon hillock (as it's the one which finally matters?). I mean does measuring gradient potential at a defined area is of any interest or is it just another piece of research making no use for neuroscience researchers? (I don't know whether it's useful to synapse plasticity research and all)
Measuring voltage at a synapse gives you a measure of the input to a cell.
Measuring voltage at the axon hillock (for a typical neuron, practically the soma can substitute as well) gives you a measure of the output of a cell: how near it is to threshold and/or if it has reached threshold and produced a spike.
Measuring voltage at intermediate sites in the dendritic tree can be a measure of spatial integration, which can be quite complex.
All of these measuring sites can be of interest, though there is a lot of variance in how difficult each will be.