This paper:
http://www.dadm.alzdem.com/article/S235 … 2/abstract
References 'Plasma neuronal derived exosomes'. But I thought exosomes were extracellular vesicles that were released by cells, and found in humours rather than within cells; but, with the limited knowledge I have, I understood this phrase to refer to exosomes that are present within the cytoplasm of neurones? Or what do they refer to?

Exosomes are extra cellular vesicles and in this case were isolated from plasma. The vesicles may carry, either on their surface or internally, markers which give clues about what types of cells they've come from which is how the authors have isolated them and worked out that they come from neuronal cells. However, depending on when you harvest cells you may still find exosomes inside them i.e the cells haven't released them yet.