MMN x MMR - mismatch negativity versus mismatch response:
How are the concepts related and what is the difference between them?
MMN/MMR refer to responses during an oddball paradigm. The typical arrangement of this sort of paradigm is to have a sequence of stimuli, for example, a sequence of tones of one frequency, followed by either the same tone (standard) or a different tone (oddball).
For EEG, they are the same thing. Mismatch negativity is a particular response in the EEG observed as the difference in response to an "oddball" compared to the same stimulus when it is a standard.
"Mismatch response" is a more general term that would include, for example, an increase (or simply a change) in neuronal firing in response to the oddball vs. standard, or a change in functional connectivity, etc.