Nasser,

What is the response you are looking to capture, is it an eye movement or a finger movement? One suggestion is to capture EMG and then analyze the ERP with respect to the onset of muscle activity. There will be a slight delay due to the arrival of the efferent volleys from M1, but this is most commonly used with movement-related potential. I don't know of any specific toolboxes that can evaluate the signal and monitor for movement-related potentials. 

Check the following publication, although this deals with self-initiated movements, they discuss a few methods for capturing the onset. 

 http://www.ncbi.nlm.nih.gov/pubmed/16876476

Currently I am using a force platform to determine the onset of movement with respect to my movement-related potential, and then will be using EMG for a follow-up study. I believe the literature leans towards using EMG as a gold standard, however.

Hope this helps,

Dear Christopher

Thanks for your answer.

But, as you know EEG and EMG acquisition systems are not synchronous. Also their sampling frequency may be different. Therefor we will not have the exact onset time. ay

Dear Stephen

Suppose we are using a separate system for EMG acquisition. 

How should we make it synchron with EEG? what about sampling frequency?

Dear Nasser,

there are several systems that allow you to record different physiological signals in a synchronized fashion (Brain Amps plus EXG, Biopac etc.).

However, if you have different systems that cannot be connected hardware-wise then you might want to look into the lab streaming layer (LSL) architecture that allows you to synchronize different data streams even with different sample rates. You will find this approach as open source in Github:

https://github.com/sccn/labstreaminglayer

and a video explaining the approach by Christian Kothe who programmed the method:

https://www.youtube.com/watch?v=Y1at7yrcFW0

We use this in our lab to synchronize motion capture with EEG and head mounted VR for mobile brain/body imaging experiments.

Best,

Klaus

Nasser,

In my studies I have constructed an external trigger, a simple circuit that closes when I depress a button, and it sends a 5V TTL signal to my EEG amp and is also hooked up to the EMG amp. (I can send you a picture of the setup in a message)

My current project is not using EMG, but using a force platform, and I am synchronizing the data in the same manner, the button sends a synchronous signal to the force platform amp, to begin data collection for the trial, and also a TTL pulse that is marked in my online EEG data, which will be used to make initial epochs for artifact rejection. 

With regard to the sampling frequency, try to keep them the same, this will make it easiest to synchronize the signals from a signal analysis perspective. My EEG is collected at 1000Hz and EMG is also at 1000Hz, so I am confident they occurred at the same time, although I will be downsampling to 200Hz later in EEGLAB. 

What EEG amp are you using? Also, EMG amp?

It takes a little more engineering, and if you aren't comfortable doing this, the method that Klaus had mentioned is an equally effective alternative!

Hi Nasser, the onset latency of movement-related ERP components can be measured with jackknife-based procedures, which are relatively straightforward and well-established:

http://www.ncbi.nlm.nih.gov/pubmed/11577905

http://www.ncbi.nlm.nih.gov/pubmed/9499711

cheers

Tobi

Hi, you can solve any triggering/ marking issue using a device like this https://www.braintrends.it/devices.html with a precision down to the millisecond and the possibility to send trigger using also custom interfaces like pedals, buttons and inertial movement units. In your case i would racommend a button that is pressed before the action and is released by the movement onset, triggering the amplifier.