Help with opening a .set file(a filtered eeg .edf file) and computing the power for each frequency band

Hello!

Please I need help with computing the power for each frequency band of an eeg signal. The initial filedata I have is in .edf format, which I filtered and is now in .set format. I found this code online;

% This example Matlab code shows how to compute power spectrum of epoched data, channel 2.

[spectra,freqs] = spectopo(EEG.data(2,:,:), 0, EEG.srate);

% Set the following frequency bands: delta=1-4, theta=4-8, alpha=8-13, beta=13-30, gamma=30-80.

deltaIdx = find(freqs>1 & freqs<4);

thetaIdx = find(freqs>4 & freqs<8);

alphaIdx = find(freqs>8 & freqs<13);

betaIdx = find(freqs>13 & freqs<30);

gammaIdx = find(freqs>30 & freqs<80);

% Compute absolute power.

deltaPower = mean(10.^(spectra(deltaIdx)/10));

thetaPower = mean(10.^(spectra(thetaIdx)/10));

alphaPower = mean(10.^(spectra(alphaIdx)/10));

betaPower = mean(10.^(spectra(betaIdx)/10));

gammaPower = mean(10.^(spectra(gammaIdx)/10));

But I've just been trying to figure out how to open my .set file in matlab and perform the necessary calculations.

I will greatly appreciate anyone's help on this. Thanks

Answer 1

[Rishav]

Hi Toni,

To open the EEG data from a .set file, you can use the EEGLAB toolbox in MATLAB.

You can download and install the EEGLAB toolbox from the below mentioned link:

https://www.mathworks.com/matlabcentral/fileexchange/56415-eeglab

After installing the EEGLAB toolbox, follow the steps mentioned below:

• Open MATLAB and start EEGLAB by typing 'eeglab' in the MATLAB command window. This will open the EEGLAB GUI.
• In the EEGLAB GUI, click on 'File' and then select 'Load existing dataset'.
• Navigate to your .set file and open it.

After loading your EEG data, you can compute power for each frequency band using EEGLAB's functions. Here is an example:

% Set the frequency bands.
freq_bands = [1 4; 4 8; 8 13; 13 30; 30 80];

% Initialize variables to store power values.
deltaPower = zeros(1, EEG.trials);
thetaPower = zeros(1, EEG.trials);
alphaPower = zeros(1, EEG.trials);
betaPower = zeros(1, EEG.trials);
gammaPower = zeros(1, EEG.trials);

% Loop through trials and compute power for each frequency band.
for trial = 1:EEG.trials
    % Extract data for the current trial and channel (e.g., channel 2).
    trial_data = EEG.data(2, :, trial);
    
    % Compute the power spectrum.
    [spectra, freqs] = spectopo(trial_data, 0, EEG.srate);
    
    % Compute power for each frequency band.
    for band_idx = 1:size(freq_bands, 1)
        band_range = freq_bands(band_idx, :);
        band_idx_range = find(freqs >= band_range(1) & freqs <= band_range(2));
        band_power = mean(10.^(spectra(band_idx_range) / 10));
        
        % Store the power in the appropriate variable.
        switch band_idx
            case 1
                deltaPower(trial) = band_power;
            case 2
                thetaPower(trial) = band_power;
            case 3
                alphaPower(trial) = band_power;
            case 4
                betaPower(trial) = band_power;
            case 5
                gammaPower(trial) = band_power;
        end
    end
end

This script will compute the power values for each frequency band in separate variables.

Thank you,

Rishav Saha