My teeth brushing touched some surface with what looks like old paint...can i be harmed if use it again? i am worried with brain damage

Unlikely: You are probably referring to heavy metal poisoning from the paint, however it is very unlikely that any heavy metal transfer would occur from merely touching a toothbrush to old paint. The toothbrush would most likely be safe to use. Hope this helps!

Paint: The concern with paint is the old fashioned kind that was lead based. That kind went out of production decades ago. If you ate large amounts of old paint there could be a problem, but just touching the paint with your t'brush would not transfer enough lead to cause toxicity. Just wash your t'brush thoroughly before the next time you use it. And if more than 3 months old, time for a new one anyway.