Two further comments, Erik:

1. I said in my first comment that our personal abstract idea of a dog is the set intersection of all the nerve networks that represent more specific ideas of dogs, but it is also, of course, the set union of all those other networks. That is, we have both a "bare bones" idea of dog and a much wider idea of dogs.

2. Where ideas exist in our human supra-organism, outside our individual brains, is in all the the cultural artifacts that we have created about dogs -- stories, movies, sculptures, etc. But those are passive representations of aspects of our dog ideas. They activate and modify in our individual brains the nerve networks that are our individual ideas about dogs. The cultural artifacts are created by individual brains (sometimes working together) and they also tend to give us similar experiences about dogs, which are what keep our individual concepts of dogs -- represented by nerve networks in our individual brains -- similar.