Previously we counted "units" by the number of different nerves tested. For example, a sensory test of the ulnar nerve and medial nerve, even if performed on multiple places along the same nerve, was coded as 95904 x 2 units. You still count the different tests the same, but instead of putting multiple units on the code for that specific test, you count the total number of tests done, and select the code based on that number. In above example, this is 2 studies (1 ulnar sensory test, 1 medial sensory test), which goes with code 95907 (1-2 studies).
If you look at Appendix J in the CPT book, any study that is listed can be counted as a separate study.
Hope this helps!