There are 2 kinds of nerve pains. One effects the thumb and neighboring finger,the other effects the outer fingers. Both are caused by nerve compression, which may be carpal tunnel or other nerve. Sorry don't recall the name of the other nerve.

Keys to preventing are:
1. vary positions frequently
2. keep weight, i.e, bar, out of the center of the notch between the thumb and next finger.
3. keep wrist as straight as possible, i.e. don't rotate the hand upwards to get into drop position.
4. something like ironman gloves can really help but still need to watch positioning.
5. decrease weight on hands by changing seat/handlebar positions. One mm at a time, this is a small amount, like 1/8", until you find some relief.

What I find works is to keep weight on the pad part of the thumb hand muscle. It took me about 3 days to keep from either putting bar in natural normal place, between the thumb and next finger or cocking upwards the hands. If you find any tingling or numbness, you need to keep working as you are doing something wrong with positioning and need to get that fixed before have permanent damage.