" We possess no criterion which enables us to distinguish exactly between a psychical process and a physiological one, between an act occurring in the cerebral cortex and one occurring in the sub-cortical substance; for 'consciousness', whatever that may be, is not attached to every activity of the cerebral cortex, nor is it always attached in an equal degree to any particular one of its activities; it is not a thing which is bound up with any locality in the nervous system. "

― Sigmund Freud , The Standard Edition of the Complete Psychological Works, 24 Vols