1
$\begingroup$

I am trying to understand how to analyze ERP (Event-Related Potentials) from EEG recordings in focus on P-300 waves.

I have come up with a few questions which I hope you might be able to help with:

  1. I assume that the number of repetitions af the stimulus should give better results, but I am not sure why. On one hand, it should help because avaraged results are usually better in neurosciences. On the other hand, maybe there is an unwanted adaptation effect of the subject? So, are repetitions wanted in this kind of experiment?

  2. There are time points in which I didn't expect P300 but the brain activity was not 0. I understand that there is always a background activity in the brain, but maybe there is more to it? And if so, are there certain frequenciess that are more likely to happen under these conditions?

  3. When I analyze the data using an avarage response, should I assume anything on the P300 response?

  4. What is the recommended Sample Rate I should use. I guess there should be an advantage for high sample rate for more resolution bur I am not sure about that. Am I right, or maybe a lower sample rate has advantages thst I am not aware of?

$\endgroup$
1
$\begingroup$

So, are repetitions wanted in this kind of experiment?

Yes: repetitions reduce random noise and increase the chance to tell artifact from response. Adaptation is a serious issue, typically becoming apparent by decreasing amplitudes, or even skipped responses. Reading the existing literature and/or performing experiments with various stimulus intervals may help to identify adaptation effects, if any.

...there is allways a background activity in the brain...

Correct - if not, you are either not recording properly, or subject is brain dead.

are there certain frequencys that are more likey to happen under these conditions

If you repeat your recordings and average them out, this is not an issue. Otherwise, yes, FFT analysis shows several frequency bands, dependent on the state of the subject. For example, awake subjects show primarily fast beta activity (13-30 Hz), drowsy or sleeping subjects much slow-wave alpha (1-4 Hz).

should I assume anything on the P300 response?

In short: The P300 response is most commonly elicited in an "oddball" paradigm when a subject detects an occasional "target" stimulus in a regular train of standard stimuli. The P300 wave only occurs if the subject is actively engaged in the task of detecting targets (Picton, 1992).

What is the recommended sample Rate I should use. I guess there should be an advantage for high sample rate for more resolution bu[t] I am not sure about that. Am I right, or maybe a lower samp[le] rate has advantages th[a]t I am not aware of?

The higher the sample rate, the better. Downsampling can always be done later. Typically 1000 Hz is sufficient for fast responses. For a P300 this should already be kind of an overkill.

Reference
- Picton, J Clin Neurophysiol (1992); 9(4): 456-79

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.