Index to your mind
Think about your mind maps. They are not your thoughts, they are representations of your thoughts, just as a map of a city is not the city itself. Many times you only have to see one word in a map, and it brings along a whole bunch of memories. The word acts as a pointer or a trigger to your memories, but the actual memories are still only in your mind. In this sense, the mind maps you create are an index to your mind.
Consider a book. How do you know what’s in it? How do you find the page containing the information you are looking for? You can browse through the pages, but often there is an index or table of contents to help you. They are easily accessible and they help you to quickly jump from one place in the book to another, without flipping through every single page searching for the right one.
Now think of your memory. How do you know what’s in there? How do you actually find anything in there? Do you think an index could help you with that? An index also helps you to consciously jump from one set of thoughts to another, like the index and table of contents in the book. The only thing is we don’t come to this world equipped with such a mind index (a mindex?), so we have to build one for ourselves.