Bug report: Cannot import Nihon Kohden .eeg files (Unrecognized field name "hdr")

[kotaaraki]

Hello Brainstorm Team,

I am currently unable to import Nihon Kohden EEG files (.eeg). This used to work perfectly fine in the past. Currently, even old .eeg files that I successfully imported before are throwing the same error, so the files themselves should be intact (all related files like .pnt, .log are also in the same folder). Updating Brainstorm to the latest version today did not solve the issue.

Here is the error message. (The first line is in Japanese, which translates to "Unrecognized field name 'hdr'"):

Plaintext

***************************************************************************
** Error: Line 445: フィールド名 "hdr" が認識されません。
** ** Call stack:
** >in_fopen_nk.m at 445
** >in_fopen.m at 139
** >in_data.m at 107
** >import_data.m at 196
** >bst_call.m at 28
** >tree_callbacks.m>@(h,ev)bst_call(@import_data,[],[],[],iStudy,iSubject) at 687
***************************************************************************

My Environment:

• OS: macOS (Apple Silicon M4 Pro)

• Brainstorm version: 23-Mar-2026 (and latest)

• MATLAB version: R2025a

Could you please look into this? Let me know if you need any sample files for debugging.

Thank you,

[edelaire]

Hello,

Sorry about that. The issue is linked to our recent change in how we read the date of the acquisition.

Could you please share a file example with us so we can double check what is going wrong ?

[kotaaraki]

Hi Edelaire,

Thank you for the quick response! That makes sense.

I have prepared a dummy dataset that reproduces the error. I zipped all the associated files (including .EEG, .21E, .pnt, .LOG, etc.) together. You can download it from the link below:

NK_test_data.zip

Please let me know if you need anything else to debug this. Thank you for your help!

[edelaire]

Hello,

Sorry for the delay. We merged a fix to brainstorm earlier today. Please update brainstorm and try again.

Thanks a lot,

Edouard

[kotaaraki]

Hi Edelaire,

Thank you so much for the quick fix! The previous hdr error is completely gone and the files are being read correctly.

Thanks again for your great support!