My 5 year old mutt has seizures. What are the causes & prevention?

I rescued him when he was about 8 months old, but the damage had already been done. He was severly abused, beaten, taped in a box at night, lit on fire (he has long, beautiful curly hair) and choked. He has seizures out of the blue, and years back I had him on seizure meds, that altered him so bad, he wasn't my baby anymore. So we took him off. I am taking him back to the vet tomorrow to see what we can do, but while I'm wide awake (he just had a seizure) I wanted some info on seizures. Any prevention? Causes? Any info would be greatly APPRECIATED. He is about 40 lbs and the love of my life. Not only did I save his, he saved mine. I am infuriated about animal abuse & pray for the end of it. Thanks for your time!