Here is a quote from G Leibniz (which I found in a book review by Galen Strawson, the book was "Soul Dust" by psychologist N Humphrey):
'[C]onsciousness, [said Leibniz], "cannot be explained on mechanical principles, ie by shapes and movements…. imagine that there is a machine [eg a brain] whose structure makes it think, sense and have perception. Then we can conceive it enlarged, so that we can go inside it, as into a mill. Suppose that we do: then if we inspect the interior we shall find there nothing but parts which push one another, and never anything which could explain a conscious experience."