How much exposure to gasoline fumes is required before brain damage occurs?

[Hopeimokay23]

When I was about 13 I stayed over at a friend's house for a weekend. That week at school we'd heard some class mate talk about how you can get "high" off of petrol fumes and being curious and somewhat stupid kids we decided it sounded like a laugh and that we'd try it. My mate went first, took 3 big "huffs" and in 20 seconds was stumbling around laughing his head off, I somewhat timidly took 2 small sniffs that burnt my nose but didn't give a hit, if I'd known the dangers at the time I never would have done what I did next but I was a stupid kid and had no idea at the time that it could cause permanent neurological damage, anyway I proceeded to take another deep 2 or 3 "huffs" through my nose and then put the can down thinking it hadn't done anything, after about 30 seconds I got an intense feeling of warmth, dizziness like I'd stood up too quickly and I lost perception of my body and myself for about 2 seconds, this whole sensation lasted a brief 10 seconds and afterwards I felt relaxed and giddy and then after about 10 minutes I got an intense headache, felt nuaseus and some anxiety, like my body was telling me what I did wasn't good for it, it was really scary so I never did it again and haven't touched any inhalents, drugs or alcohol since (I'm 17 now) my friend however, continued to do it another 4 times afterwards before he stopped. It wasn't until recently that I found out that petrol fumes cause brain damage when I met a guy who has damage from it, and he basically comes across as an intellectual handicap person. This terrified me and ever since I've been worrying myself sick that I did some permanent neurological damage to myself, is this possible from a one off time? How exactly does petrol fumes interact with the nervous system in order to do damage to it? If I had done some damage what symptoms could I expect to see manifesting themselves?