<div dir="ltr">Dear Andrei and Hui-bin,<div><br></div><div>I'm still not sure what should be discussed here, but let me add my thoughts exploratorily. Probably what I mean is in a primitive and practical sense.</div><div><br></div><div>When I check IC freq spectra for cluster cleaning in STUDY, I visually check their 1/f-ness. They can have peaks at theta or alpha, sometimes in both alpha and beta together (typically mu shows this and rarely occipital alpha does too), but otherwise they show a more or less smooth slope from top left to the bottom right. I know these freq band specific peaks are on the top of 1/f slope, but I don't know if I should call this to be non-1/f (assuming that spec plot continues up to the nyquist frequency).</div><div><br></div><div>If the elbow of the curve is too deep, I would suspect some kind of eye component. If the curve shows a broad peak that is higher than delta and theta at around 30 Hz, or shows a square-root-sign shape over 2-30Hz, I suspect EMG. They do not follow 1/f pattern.</div><div><br></div><div>Makoto<br></div><div><br></div><div><br></div></div><div class="gmail_extra"><br><div class="gmail_quote">On Fri, Sep 26, 2014 at 6:59 PM, Andrei Medvedev <span dir="ltr"><<a href="mailto:am236@georgetown.edu" target="_blank">am236@georgetown.edu</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Hi All,<br>
<br>
Let me suggest a different opinion.<br>
<br>
First of all, evoked/induced activities are relative measures. There<br>
is no reason to believe that RELATIVE changes in power at different<br>
frequencies would obey the same 1/f law unless in a very special case.<br>
<br>
Second, even if we consider absolute (not relative) power changes, it<br>
seems to me that, in general, evoked/induced activity would not follow<br>
the 1/f power law. Why? The 1/f law describes a relationship between<br>
powers at different frequencies within the total spectral content of<br>
EEG. To keep their obedience to this law, ALL frequencies should<br>
experience SIMILAR changes after the stimulus i.e., to increase or<br>
decrease proportionally. But this is obviously a rare case. If we<br>
evoke/induce something in the brain by a stimulus, this something, for<br>
example, can be a very narrow-band process i.e., an increase in power<br>
at a particular frequency (say, 40 Hz) while all other frequencies<br>
would not increase at all or even decrease (this happens quite often).<br>
This means that the pre-stimulus 1/f power law would be broken after<br>
the stimulus (for a relatively short time when we observe a RESPONSE).<br>
<br>
Also, one should keep in mind that evoked/induced activities are not<br>
stationary processes so any stimulus-related power modulations do<br>
themselves change from one moment in post-stimulus time to another<br>
(again, the concept of a RESPONSE constrained in time applies).<br>
<br>
As for the second question, I believe the evoked change can<br>
(theoretically!) be equal to the induced change but again, speaking<br>
more generally, it's more likely they would change differently<br>
depending on the underlying processes.<br>
<br>
Best,<br>
Andrei Medvedev<br>
Georgetown University<br>
<div class="HOEnZb"><div class="h5"><br>
On Fri, Sep 26, 2014 at 8:24 PM, Makoto Miyakoshi <<a href="mailto:mmiyakoshi@ucsd.edu">mmiyakoshi@ucsd.edu</a>> wrote:<br>
> Dear Hui-bin,<br>
><br>
>> Does the evoked activity and induced activity,which were calculated by<br>
>> subtracting the pre-stimulus power from the post-stimulus power at each<br>
>> frequency, follow the same law?<br>
><br>
> Generally speaking, yes.<br>
><br>
>> Is it possible that the magnitudes of the evoked or induced activity at<br>
>> each frequency are equal?<br>
><br>
> Yes, that is possible... I mean I can't think of any reason to exclude that<br>
> possibility.<br>
><br>
> I'm not sure if I'm answering to your question exactly.<br>
><br>
> Makoto<br>
><br>
> On Fri, Sep 19, 2014 at 9:12 PM, Hui-bin Jia <<a href="mailto:420247417@qq.com">420247417@qq.com</a>> wrote:<br>
>><br>
>> Hi,everyone<br>
>><br>
>> I have a question about the evoked and induced activity.<br>
>><br>
>> As we all know, spontaneous EEG activity follow " the 1/f law",<br>
>> which means the spectral power of lower band is much larger than the<br>
>> spectral power of the higher band. In rest EEG, alpha band power may be the<br>
>> largest one.<br>
>><br>
>> Does the evoked activity and induced activity,which were<br>
>> calculated by subtracting the pre-stimulus power from the post-stimulus<br>
>> power at each frequency, follow the same law? Is it possible that the<br>
>> magnitudes of the evoked or induced activity at each frequency are equal?<br>
>><br>
>> Any reply will be appreciated !<br>
>><br>
>><br>
>> Yours,<br>
>> Hui-bin jia<br>
>><br>
>><br>
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><br>
><br>
><br>
><br>
> --<br>
> Makoto Miyakoshi<br>
> Swartz Center for Computational Neuroscience<br>
> Institute for Neural Computation, University of California San Diego<br>
><br>
> _______________________________________________<br>
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</div></div></blockquote></div><br><br clear="all"><div><br></div>-- <br><div dir="ltr">Makoto Miyakoshi<br>Swartz Center for Computational Neuroscience<br>Institute for Neural Computation, University of California San Diego<br></div>
</div>