What do the Axx and $Axx channel names represent in Nihon Kohden EEG files?

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1

Hi,

I’m using MNE-Python’s read_raw_nihon() to read Nihon Kohden EEG files, and I’m trying to understand the meaning of some channels that aren’t standard 10–20 EEG electrodes.

For example, one of my recordings contains:

FP1 FP2 F7 F3 C3 C4 FZ F4 A23 T3 CZ T4 T5 P3 A22 P4 T6 O1 O2
E PZ F8 A1 A2 ECG1 ECG2 ROC LOC emg R emg L T1 T2 T9 T10
A34 A35 A36 DC01 DC02 DC03 DC04 A37 A38 $A1 $A2 A39

I’m familiar with the standard EEG channels, as well as A1/A2, ECG, ROC/LOC, and EMG, but I’m not sure what the following represent:

A22 A23
A34 A35 A36 A37 A38 A39
$A1 $A2
DC01 DC02 DC03 DC04

Are these Nihon Kohden-specific input/channel identifiers? If so, is there a mapping or documentation that explains what physical electrodes or signals they correspond to?

Since read_raw_nihon() was implemented specifically to parse these files, I was wondering whether the information needed to interpret these channel names is available in the Nihon Kohden file format or perhaps in the .21E/other companion files.

Any pointers from the MNE developers or anyone familiar with the Nihon Kohden reader would be greatly appreciated.

Thanks!

2

DC01 to DC04 are separate, DC-coupled channels with an inputrange up to 3V.

3

ty for you comment. what i noticed is that they seem to represent events. like push button pressed by nurse i believe