<P> When recording a more detailed EEG with more electrodes, extra electrodes are added using the 10% division, which fills in intermediate sites halfway between those of the existing 10--20 system . This new electrode - naming - system is more complicated giving rise to the Modified Combinatorial Nomenclature (MCN). This MCN system uses 1, 3, 5, 7, 9 for the left hemisphere which represents 10%, 20%, 30%, 40%, 50% of the inion - to - nasion distance respectively . The introduction of extra letter codes allows the naming of intermediate electrode sites . Note that these new letter codes do not necessarily refer to an area on the underlying cerebral cortex . </P> <P> The new letter codes of the MCN for intermediate electrode places are: </P> <Ul> <Li> AF--between Fp and F </Li> <Li> FC--between F and C </Li> <Li> FT--between F and T </Li> <Li> CP--between C and P </Li> <Li> TP--between T and P </Li> <Li> PO--between P and O </Li> </Ul> <Li> AF--between Fp and F </Li>

Where are the electrodes placed for an eeg