Hi and thanks for opening this thread. Here's the mystery:

I used to have a good guitar technique and played electric (thumb over the neck, i.e. blues/rock etc) and also classical (thumb behind the neck, i.e. classical posture). Then I played in a rock band with my guitar real low and my technique got real 'lazy', i.e. my thumb would always be over the neck, even for playing barre chords (ala Hendrix etc).

The problem is this:

I have been trying to start using the classical posture again (important for runs, wide intervals, awkward chords etc) but when I try to play a note with my index (1st) finger my other 3 fretting fingers curl up and dampen the strings. I can employ my 2,3,4 fingers fine and can even do runs etc using just them....but I literally cannot play a note using my 1st finger without my other fingers curling inwards. My fingers sometimes click as well, which is something I never used to experience.

I've been struggling with this problem on and off for a few years now and have recently discovered that I am able to play clear notes using my index finger...if I hold my 2nd finger back using my 3rd! In other words, I literally cross my 2nd and 3rd fingers (3rd nearest my palm) and my 1st finger behaves itself just like it used to in the past. Of course, it takes time and effort to cross my middle 2 fingers, so incorporating this into my technique is out of the question (it would look cool though to play like that though lol).

I once saw a specialist (doc) regarding this problem (at the time I thought it was some form of tendonitis) and after messing about with my hand she claimed there is no apparent damage.

Um, that's it. Thanks for reading this and any useful help/suggestions will be hugely appreciated.

Are you able to post a picture, i'm finding it difficult to imagine how it looks.

Do you have any control of your fingers when they curl up? With enough practice (simply self control exercises with the hand) you can get control, much like finger independance.

I hope that helped, I can't be 100% sure unless I see what's happening