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I have opened the file in Matlab and am using MNE Python too. This is a processed EEG file in Matlab data format instead of raw EEG (Screenshot 1). Screenshot 1: struct of the 801_1_PD_REST Screenshot 1: struct of the 801_1_PD_REST

Now the problem is that inside the Matlab data file, the values inside EEG are very large (see screenshot 2), and what are their units? I have read on the internet that generally the microvolt as a unit is used for EEG analysis, but these are too large values to be in microvolts, so what are these values exactly? Even in the organized data file, the values don't look like voltages (see screenshot 3) Screenshot 2: Inside the 801_1_PD_REST Screenshot 2: Inside the 801_1_PD_REST

Screenshot 3: Organized data with eyes closed Screenshot 3: Organized data with eyes closed

I have also opened some raw EEG files with MNE in Python (https://neuraldatascience.io/7-eeg/mne_data.html).

and accessing the data, the general unit of every channel voltage is already mentioned (see screenshot 4), and the data inside it also looks like EEG voltages (see screenshot 5). But in the processed data, what are those values? I don't understand. They can't be voltages, right? Also as the unit mentioned in micro volt in screenshot 4 so if the value is -7.68e-6 it meant -7.68 micro volts or -7.68e-6 micro volts

Screenshot 4: Every channel's unit is specified as microvolts and in the data actual voltages in raw eeg from IOWA out of sample dataset Screenshot 4: Every channel's unit is specified as microvolts and in the data actual voltages in raw eeg from IOWA out of sample dataset

In 63th(array indexing from 0) channel printing out first 10 data In 63th(array indexing from 0) channel printing out first 10 data

Dataset Description:

Methods: We included a total of 41 PD patients and 41 demographically-matched controls from New Mexico and Iowa. Data for all participants from New Mexico (27 PD patients and 27 controls) were used to evaluate insample LEAPD performance, with extensive cross-validation. Participants from Iowa (14 PD patients and 14 controls) were used for out-of-sample tests. Our method utilized data from six EEG leads which were as little as 2 min long.

Paper Link: Linear predictive coding distinguishes spectral EEG features of Parkinson's disease Dataset Link: Available Data

I am working on detecting PD from EEG signals as my thesis work.

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  • $\begingroup$ @Jdip -1.2005019e+06, -1.2005019e+06, 409.47266, 3.2641602e+03 these are some of random values. No I do not have any idea even in the paper there are no details information telling what actually happened during processing. As these are all processed data instead of raw due to some processing these values became like these? and these are not clearly voltage value right? (like in screen shot 4 or 5) $\endgroup$
    – tahsin
    Jul 5 at 18:09
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    $\begingroup$ Have you tried plotting the data?? does it look like EEG?? $\endgroup$
    – Jdip
    Jul 5 at 18:43
  • $\begingroup$ @Jdip Update: there are some confusions that I may not have looked enough into the data or being just someone lazy asking here for to look into my matter no, I have tried to look into it and the values confuse me. Proof that I have actually looked into the data streamable.com/mc519p $\endgroup$
    – tahsin
    Jul 6 at 10:28

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Accessing the data requires a login that I don't have, so here is a wild guess.

It looks like the Matlab data is indeed in $\mu V$ but with a very large DC bias (which is fairly common for EEG signals). I suggest looking at the data after subtracting the mean for starters.

It's also fairly normal to leave the bias in the signal as the offset may drift over time and having access to the raw data allows applying more sophisticated bias removal algorithms.

EDIT:

I'm not sure what exactly your problem is. The data reads fine in Matlab and looks reasonable. As expected it's "noisy" with a large bias and other potential contaminants so some cleanup is likely required, but the data file itself seems perfectly fine and easy to interpret.

enter image description here

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  • $\begingroup$ here is my re upload for personal backup drive.google.com/drive/folders/… so that you can navigate better "dataset/UNM dataset/Jim rest" this location has 27 PD and 27 control and then they are organized in the "dataset/UNM dataset/Organized data" I need to work on eyes closed with all channels. $\endgroup$
    – tahsin
    Jul 6 at 5:18
  • $\begingroup$ and my another query as mentioned in the main question say for example in screenshot 5 where I have printed out some voltage values from the array the first entry prints -4.21 e -21 so it means -4.21 e -21 micro volts? or maybe look at the last entry? -7.95 e -06 in micro volts? from wikipedia en.wikipedia.org/wiki/Electroencephalography EEG should be in 10-100 micro volts. So what am I actually missing? are there noise or artifacts in the raw one so it is causing not so idea values? $\endgroup$
    – tahsin
    Jul 6 at 5:29
  • $\begingroup$ -4.21e -21 is effectively 0. I'll ask again, have you even tried plotting the data? $\endgroup$
    – Jdip
    Jul 6 at 6:43
  • $\begingroup$ @Jdip sorry for not replying to your comment in the main thread. No I have not tried plotting it actually accessing the data with python is quite challenging for me not getting much resources on that how to access the struct of a matlab data file using python.If you are interested to look at the data here is the direct link, organized data : drive.google.com/drive/folders/… (eyes closed one) , and 27 PD and control patient's processed EEG: drive.google.com/drive/folders/… $\endgroup$
    – tahsin
    Jul 6 at 8:16
  • $\begingroup$ I have already looked into data look at screenshot 4 and 5. I have accessed mat file too using scipy and mat73 too. I said I have trouble accessing the struct when I am coding with Python in Jupyter lab imgur.com/f0h9qJL I have also used mat73 -> imgur.com/I0vuJhj I have trouble looking into the matlab struct with python and did not manage to find any good resources on that. Of course I have come here after a whole lot of google search and failed to get my answer @Jdip $\endgroup$
    – tahsin
    Jul 6 at 9:48

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