Just saying stuff doesn't make it so (that's something the theists do), and you do say 'seems' which is a type of act of faith. And again you have no direct way of judging that your intelligence (an undefined term) is associated with an emergence from the collective actions of your neurons.
Not sure what you mean by 'direct'. The brain has been studied now for a century at least, and we know that brain damage, whether caused by injury or disease, can have devastating consequences for various cognitive functions. For example, I know someone who woke up one morning not knowing who she was. I suppose you might argue that that is not intelligence, but if you sit with some people with dementia, there seems little doubt that some of their mental faculties are impaired. I suppose you could still argue that there is 'something else' which determines cognition and intelligence, such as the soul, but we are still waiting for a research project into that.
Studies of children also seem to show that the maturing brain leads to developments in cognition, for example, language ability, perceptual skills, conceptual resources, and so on. Again, you could argue that it's not the brain wot done it, I guess.