In carrying out experiments related to imagine the movement of a hand using C3 and C4 electrodes.
Hi, Wojciech. Will you please explain more detailed the question: the problem in the experimental design or electrodes using for EEG registration? What do you want to see?
Regards, Elizaveta
Thank you for the answer and the question. My colleague tries make a simple experiment about imagine the movement of a hand, but her experiment has failed. I was thinking that a hairy place of a skull was a reason, but professor Don Rojas said that: "Unusually thick hair can physically interfere with good coupling between the electrode and scalp when using gels and other electrolytes. But normally hair is not a problem for EEG. It is easier to place electrodes on bald patches but in my experience the impedance are often higher there."
Describe of the experiment:
She recorded 100 samples with imagine the movement of the left hand. Then, she recorded another 100 samples with idea of movement of the right hand. The samples were recorded for the two channels (C3 and C4 in International System of electrode placement 10-20). She averages samples and obtains:
A - The mean signal for C3 with movement of the left hand,
B - The mean signal for C3 with movement of the right hand,
C - The mean signal for C4 with movement of the left hand,
D - The mean signal for C4 with movement of the right hand,
Afterwards, she used FFT (Fast Fourier Transform) to obtain the Mu band (8-13Hz).
Finally, she computes power of the signal (formula is attached).
In Figure 1, she drafts Power of A and Power of B in the temporal domain.
In Figure 2, she drafts Power of C and Power of D in the temporal domain.
In her experiments in Figure 1 and 2 the differences are negligible, but for data from repositories everything is OK. It means that if we imagine the movement of the left hand than we see the loss of power for C in respect to A (in the temporal domain).
My conclusions were that the procedure of recorded data must be incorrect. I thought that hairy place of a skull can be the problem, but after the answer of professor Don Rojas, the last thing is imagined the movement of a hand. How can you imagine the movement of a hand. Maybe it is the real problem in this experiment.
This experiment will be successful if she moves a hand, but she wants imagine the movement of a hand. This is a very simple sentence: "Imagine the movement of the left hand", but I don't sure that is easy to imagine the movement. For example, is it enough to imagine that we reach something our left hand?
Wojciech, there is a difference between imagination of self movements and mentally observed movements of other person. The differents related to mirror system activity, as far as I remember.
try this new paper, may be it'll be use ful
Goal or movement? Action representation within the primary motor cortex (pages 3507–3512)
Andrea Cavallo, Giulia Bucchioni, Umberto Castiello and Cristina Becchio
Article first published online: 20 AUG 2013 | DOI: 10.1111/ejn.12343
http://onlinelibrary.wiley.com/doi/10.1111/ejn.12343/abstract
Single Trial Classification of Motor Imagination Using 6 dry EEG electrodes
Popescu F, Fazli S, Badower Y, Blankertz B, Muller KR
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