I have watched Matt Duff's excellent YouTube video on how to calculate the noise of an instrumentation amp circuit. He shows how to calculate the resistor noise and current noise for a resistor in series with each input to the in amp. I would like to know how to calculate the noise when the inputs are connected to opposite ends of a current sense resistor having resistance R. Can I treat that as if I am measuring a voltage at a point located in the middle of the resistor, with a resistance of 1/2 R in series with each input?

I'm glad the video was helpful! You can do as you say, but you should get the same answer as if you just assume one resistor of resistance R.

Imagine two voltage sources in series between the in amp terminals:

- A voltage source that is the I*R you are trying to measure

- A noise source that is the thermal noise caused by R

Matt