Hi,

No question about the code per se, but I could use some help understanding the use of the inverse operator for resting state EEG data.

Is there any advantage in calculating the source PSD values/epochs on inverse operators derived from narrowband filtered data (delta, …, beta) over using the same inverse operator derived from broadband filtered data (1.5-40 Hz)?

Some context: the data is resting state and I intend to use the same noise covariance matrix (identity matrix) regardless of the frequency range of interest, which makes me believe I only need to compute the inverse operator for my broadband cortical signal, and not for each band seperately.

The reason I am asking is that I observe a small difference between both methods, e.g. for delta:

Method 1:inverse operator derived from broadband filter with fmin = 1.5 Hz and fmax = 4 Hz

Average power (6590,8)

```
[[9.56763174e-10 1.24931190e-09 1.52772841e-09 ... 1.76038614e-09
1.67219170e-09 1.64530438e-09]
[8.26087445e-10 1.17333296e-09 1.40139410e-09 ... 1.64014080e-09
1.48380376e-09 1.40014022e-09]
[8.47870981e-10 1.21117137e-09 1.49278952e-09 ... 1.78950599e-09
1.52176490e-09 1.57311583e-09]
...
[6.74411834e-10 9.78748067e-10 1.17202800e-09 ... 1.46453494e-09
1.35993799e-09 1.39948656e-09]
[6.40588818e-10 9.29214005e-10 1.11440379e-09 ... 1.39675566e-09
1.29619498e-09 1.33795859e-09]
[6.74045211e-10 9.75321145e-10 1.17137386e-09 ... 1.45750841e-09
1.35316089e-09 1.38864280e-09]]
```

Method 2: inverse operator derived from passband filtered epochs (delta) with fmin =1.5 Hz and fmax = 4Hz

Average power (6590,8)

```
[[8.12947488e-10 1.00539618e-09 1.14412079e-09 ... 8.30747087e-10
6.24956392e-10 4.70511543e-10]
[6.93727387e-10 9.29477531e-10 1.04234848e-09 ... 7.98024045e-10
5.65210628e-10 3.99083164e-10]
[6.93049943e-10 9.34984033e-10 1.08525464e-09 ... 8.94035755e-10
5.71421773e-10 4.49558812e-10]
...
[5.62166366e-10 7.64839217e-10 8.61073072e-10 ... 7.08300891e-10
5.06656670e-10 3.99428148e-10]
[5.33802551e-10 7.25919640e-10 8.18221537e-10 ... 6.75188002e-10
4.81844740e-10 3.81201676e-10]
[5.62300131e-10 7.62615692e-10 8.60526621e-10 ... 7.05796791e-10
5.05995182e-10 3.97951712e-10]]
```

As you can see, both methods lead to different results. In both cases, I use the function mne.minimum_norm.compute_source_psd_epochs.

Is only the second method here correct or are both correct?

Thanks!