# Weird power spectral density plot **URL:** \ **Category:** Support & Discussions\ **Tags:** eeg, visualization\ **Created:** [April 8, 2024, 7:17am UTC](https://mne.discourse.group/t/weird-power-spectral-density-plot/8599 "2024-04-08T07:17:59Z")\ **Posts on this page:** 12\ **Page:** 1
**Author:** ![Daniel-Gong](https://avatars.discourse-cdn.com/v4/letter/d/eb8c5e/32.png) [@Daniel-Gong](https://mne.discourse.group/u/Daniel-Gong)\ **Post date:** [April 8, 2024, 7:17am UTC](https://mne.discourse.group/t/weird-power-spectral-density-plot/8599/1 "2024-04-08T07:17:59Z")
Dear all, While inspecting the EEG power spectral density from one subject, I got this super weird pattern. I searched everywhere but still cannot figure out what is happening here. I was wondering if it is related to the filters I used - I applied [0.1Hz,80Hz] band-pass filters to the data of every subject - but only this subject showed this weird pattern. If you have any idea what might be causing this, I will be more than glad to hear! Thank you! ![image](https://global.discourse-cdn.com/free1/uploads/mne/original/2X/0/0b8d388f1fcb5c5fb171b2e97777aec0016aa0c4.png) ---
**Author:** ![wmvanvliet](https://yyz2.discourse-cdn.com/free1/user_avatar/mne.discourse.group/wmvanvliet/32/100_2.png) [@wmvanvliet](https://mne.discourse.group/u/wmvanvliet)\ **Post date:** [April 8, 2024, 7:21am UTC](https://mne.discourse.group/t/weird-power-spectral-density-plot/8599/2 "2024-04-08T07:21:29Z")
looks like some oscillatory interference. Can you show us a little snippet of the continuous data? (non frequency transformed). it could be that one of the reference electrodes had poor contact. Then after re-referencing all channels are bad. ---
**Author:** ![Daniel-Gong](https://avatars.discourse-cdn.com/v4/letter/d/eb8c5e/32.png) [@Daniel-Gong](https://mne.discourse.group/u/Daniel-Gong)\ **Post date:** [April 8, 2024, 7:30am UTC](https://mne.discourse.group/t/weird-power-spectral-density-plot/8599/3 "2024-04-08T07:30:43Z")
Dear Marjin, Thank you for your reply! Here is a segment of the raw data. Seems like they also look weird. Do you have any idea what might be happening here? ![image](https://global.discourse-cdn.com/free1/uploads/mne/original/2X/1/13e0d13e03081bbb8d7f402a3623b102e025d520.png) ---
**Author:** ![Daniel-Gong](https://avatars.discourse-cdn.com/v4/letter/d/eb8c5e/32.png) [@Daniel-Gong](https://mne.discourse.group/u/Daniel-Gong)\ **Post date:** [April 8, 2024, 7:33am UTC](https://mne.discourse.group/t/weird-power-spectral-density-plot/8599/4 "2024-04-08T07:33:21Z")
Here is another segment: ![image](https://global.discourse-cdn.com/free1/uploads/mne/original/2X/d/dbf81efe4f91d81e07b24642e1f04ced0dc4baa8.png) I have no idea what those small downward spikes are… ---
**Author:** ![Daniel-Gong](https://avatars.discourse-cdn.com/v4/letter/d/eb8c5e/32.png) [@Daniel-Gong](https://mne.discourse.group/u/Daniel-Gong)\ **Post date:** [April 8, 2024, 7:38am UTC](https://mne.discourse.group/t/weird-power-spectral-density-plot/8599/5 "2024-04-08T07:38:19Z")
Here is another participant having this weird pattern. The common signature is found at around 30Hz. ![image](https://global.discourse-cdn.com/free1/uploads/mne/original/2X/4/4a4f85a44ab3cc2510d2c0a32407743bb4e5188a.png) ---
**Author:** ![wmvanvliet](https://yyz2.discourse-cdn.com/free1/user_avatar/mne.discourse.group/wmvanvliet/32/100_2.png) [@wmvanvliet](https://mne.discourse.group/u/wmvanvliet)\ **Post date:** [April 8, 2024, 8:03am UTC](https://mne.discourse.group/t/weird-power-spectral-density-plot/8599/6 "2024-04-08T08:03:58Z")
those deflections look like blinks and eye movements to me. But those wouldn’t explain the weird spectrum. ---
**Author:** ![mscheltienne](https://yyz2.discourse-cdn.com/free1/user_avatar/mne.discourse.group/mscheltienne/32/827_2.png) [@mscheltienne](https://mne.discourse.group/u/mscheltienne)\ **Post date:** [April 8, 2024, 8:20am UTC](https://mne.discourse.group/t/weird-power-spectral-density-plot/8599/7 "2024-04-08T08:20:43Z")
A weird oscillatory noise on the ref electrode, spread to other electrodes by common average reference maybe? It’s difficult to say more without seeing the data. Could you share the file with the provider of your choice? ---
**Author:** ![Daniel-Gong](https://avatars.discourse-cdn.com/v4/letter/d/eb8c5e/32.png) [@Daniel-Gong](https://mne.discourse.group/u/Daniel-Gong)\ **Post date:** [April 8, 2024, 8:46am UTC](https://mne.discourse.group/t/weird-power-spectral-density-plot/8599/8 "2024-04-08T08:46:02Z")
Dear Mathieu, Here is a copy of the raw .fif file: [30\_raw.fif](https://yaleedu-my.sharepoint.com/:u:/g/personal/dongyu_gong_yale_edu/EYGPDtSbRPlEpJs3MR9R57oBbMz2lOLX9wZbFsvZewg6pg?e=n9nuqg) ---
**Author:** ![cbrnr](https://yyz2.discourse-cdn.com/free1/user_avatar/mne.discourse.group/cbrnr/32/1409_2.png) [@cbrnr](https://mne.discourse.group/u/cbrnr)\ **Post date:** [April 8, 2024, 8:49am UTC](https://mne.discourse.group/t/weird-power-spectral-density-plot/8599/9 "2024-04-08T08:49:51Z")
Without having checked out the file, this PSD pattern usually occurs because of a large artifact (spike, overflow) in your data (the oscillatory-like behavior can also be due to aliasing). I’d check the affected data sets, and if they contain such large artifacts mark them with “BAD”. ---
**Author:** ![mscheltienne](https://yyz2.discourse-cdn.com/free1/user_avatar/mne.discourse.group/mscheltienne/32/827_2.png) [@mscheltienne](https://mne.discourse.group/u/mscheltienne)\ **Post date:** [April 8, 2024, 9:34am UTC](https://mne.discourse.group/t/weird-power-spectral-density-plot/8599/10 "2024-04-08T09:34:58Z")
There is a large discontinuity in the middle of your file: ![Screenshot from 2024-04-08 11-30-38](https://global.discourse-cdn.com/free1/uploads/mne/original/2X/c/cf5bb206e5d8c773d6435b342ddd4d49403b609d.png) Mark it as `bad_xxx` with an annotation, and you get a decent spectrum: ![Screenshot from 2024-04-08 11-33-23](https://global.discourse-cdn.com/free1/uploads/mne/original/2X/2/266170a365e07de177eca4e8aaed9ced978720f2.png) Best, Mathieu ---
**Author:** ![Daniel-Gong](https://avatars.discourse-cdn.com/v4/letter/d/eb8c5e/32.png) [@Daniel-Gong](https://mne.discourse.group/u/Daniel-Gong)\ **Post date:** [April 8, 2024, 2:38pm UTC](https://mne.discourse.group/t/weird-power-spectral-density-plot/8599/11 "2024-04-08T14:38:12Z")
Thank you so much Mathieu! This makes much more sense now! ---
**Author:** ![system](https://global.discourse-cdn.com/free1/uploads/mne/original/1X/85cc6bd2b69cb698a166dc6d880fb550510d0144.jpeg) [@system](https://mne.discourse.group/u/system)\ **Post date:** [April 15, 2024, 2:38pm UTC](https://mne.discourse.group/t/weird-power-spectral-density-plot/8599/12 "2024-04-15T14:38:24Z")
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