I want STFT and spectrogram of EEG data

I have EEG data in .txt format. Here are my steps of the task.

1. Convert .txt to .mat format.
2. Concatenat the 6 classes of files into a single .mat file.
3. Do STFT of it.
4. Plot spectrogram from that STFT.

I have seen examples of STFT with audio file. But I need it with a .mat file. How can I do that?

How can I plot the spectrogram after STFT?

Thanks in advance