[Eeglablist] about the evoked activity and induced activity

[Makoto Miyakoshi]

Dear Andrei and Hui-bin,

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.

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).

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.

Makoto



On Fri, Sep 26, 2014 at 6:59 PM, Andrei Medvedev <am236 at georgetown.edu>
wrote:

> Hi All,
>
> Let me suggest a different opinion.
>
> First of all, evoked/induced activities are relative measures. There
> is no reason to believe that RELATIVE changes in power at different
> frequencies would obey the same 1/f law unless in a very special case.
>
> Second, even if we consider absolute (not relative) power changes, it
> seems to me that, in general, evoked/induced activity would not follow
> the 1/f power law. Why? The 1/f law describes a relationship between
> powers at different frequencies within the total spectral content of
> EEG. To keep their obedience to this law, ALL frequencies should
> experience SIMILAR changes after the stimulus i.e., to increase or
> decrease proportionally. But this is obviously a rare case. If we
> evoke/induce something in the brain by a stimulus, this something, for
> example, can be a very narrow-band process i.e., an increase in power
> at a particular frequency (say, 40 Hz) while all other frequencies
> would not increase at all or even decrease (this happens quite often).
> This means that the pre-stimulus 1/f power law would be broken after
> the stimulus (for a relatively short time when we observe a RESPONSE).
>
> Also, one should keep in mind that evoked/induced activities are not
> stationary processes so any stimulus-related power modulations do
> themselves change from one moment in post-stimulus time to another
> (again, the concept of a RESPONSE constrained in time applies).
>
> As for the second question, I believe the evoked change can
> (theoretically!) be equal to the induced change but again, speaking
> more generally, it's more likely they would change differently
> depending on the underlying processes.
>
> Best,
> Andrei Medvedev
> Georgetown University
>
> On Fri, Sep 26, 2014 at 8:24 PM, Makoto Miyakoshi <mmiyakoshi at ucsd.edu>
> wrote:
> > Dear Hui-bin,
> >
> >> Does the evoked activity and induced activity,which were calculated by
> >> subtracting the ‍pre-stimulus power  from the post-stimulus power ‍at
> each
> >> frequency, follow the same law?
> >
> > Generally speaking, yes.
> >
> >> Is it possible that  the magnitudes of ‍the evoked or induced activity
> at
> >> each frequency are equal?
> >
> > Yes, that is possible... I mean I can't think of any reason to exclude
> that
> > possibility.
> >
> > I'm not sure if I'm answering to your question exactly.
> >
> > Makoto
> >
> > On Fri, Sep 19, 2014 at 9:12 PM, Hui-bin Jia <420247417 at qq.com> wrote:
> >>
> >> Hi,everyone
> >>
> >>         I have a question about the evoked and induced activity‍.
> >>
> >>         As we all know, spontaneous EEG activity follow " the 1/f law",
> >> which means the spectral power of lower band is much larger than the
> >> spectral power of the higher band. In rest EEG, alpha band power may be
> the
> >> largest one.
> >>
> >>         Does the evoked activity and induced activity,which were
> >> calculated by subtracting the ‍pre-stimulus power  from the
> post-stimulus
> >> power ‍at each frequency, follow the same law? Is it possible that  the
> >> magnitudes of ‍the evoked or induced activity  at each frequency are
> equal?
> >>
> >>         Any reply will be appreciated !‍
> >>
> >>
> >> Yours,
> >> Hui-bin jia
> >>
> >>
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> >
> >
> >
> > --
> > Makoto Miyakoshi
> > Swartz Center for Computational Neuroscience
> > Institute for Neural Computation, University of California San Diego
> >
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-- 
Makoto Miyakoshi
Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego
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