PSD different in each channel

Hi everyone, I'm working with EEG signal. I have to divided EEG signal into 3 band( theta, alpha,beta). After that, I calculate PSD for each channel of each band in one state( Ex: happy feeling). But the result shows me that PSD of each wave is not uniform.

Ex: in channel AF3 (PSD of beta > theta > alpha ) and in channel F7 (PSD of Theta > beta> alpha) .

Are the results necessarily even? ( like if in channel AF3 beta > theta > alpha then all channel must be beta > theta> alpha?)

Anyone please help me :

[Nicolò La Porta]

Hello Tran,

It depends on how different the power difference amount to.

The results are not necessarily equal but with respect to a certain condition of the subject (e.g. deep sleeping/wakefulness) or the action the subject is doing (e.g. relaxing/keeping high concentration) the power in the various bands should be similar among channels unless the subject is highly using a particular cerebral area because of the action he's doing.

Before proceeding with PSD computation be sure of filtering correctly the signal and keep only the frequencies you need.

Moreover, look for artifacts that can affect PSD and proceed with artifact removal if it is necessary

[Tran]

Thank you for your help @Nicolò La Porta, i suppose that my result was wrong but i don't know why. May I have your help? I have some function in matlab to filter and bandpass EEG but I'm not sure that i had removed all and remove artifact or not. Can you give me your address mail or something like that ( for me to contact with you easily).

Thank you, If I'm bothering you, please ignore this message.