Component naming of MEG vs. EEG My question is why we use P and N for naming positive and negative EEG component(for instance N170 or P100) but for MEG data we use M in both case, I mean M170 and M100 in this example?
EEG and MEG measure two different but related signals. While EEG records the electric activity from the scalp, MEG records changes in the magnetic field induced by electric activity in the brain. Because of this, MEG is largely insensitive to sources oriented radially, but can pick up sources oriented tangentially to the cortex. Moreover, EEG is sensitive to volume currents (i.e., the spread of currents across the brain), while MEG less so [1].

Because of this distinction, while two components can have the same latency — let's say the face-specific N170 and the M170 — the sources originating them might be different. Naming the components differently stresses this important distinction.

For reference, I recommend the following articles and books


Baillet, S., Mosher, J. C., &amp; Leahy, R. M. (2001). Electromagnetic brain mapping. Signal Processing Magazine, IEEE, 18(6), 14–30.
Hansen, P., Kringelbach, M., &amp; Salmelin, R. (2010). MEG:An Introduction to Methods. Oxford University Press, USA.