[Eeglablist] Critical pitfall of spectral power analysis?

[Gyurkovics, Mate]

I agree that these considerations do make it sound like oscillations and aperiodic activity are intricately linked, but while I'm quite sure they should interact in some situations, what we see in scalp data seems to suggest to me that they are quite independent. So maybe there is more to both oscillatory and non-oscillatory activity than just E:I balance (as discussed above too).

Best,
Máté
________________________________
Feladó: Daniele Marinazzo <daniele.marinazzo at gmail.com>
Elküldve: 2025. szeptember 3., szerda 11:02
Címzett: Gyurkovics, Mate <mategy at illinois.edu>
Másolatot kap: EEGLAB List <eeglablist at sccn.ucsd.edu>
Tárgy: Re: [Eeglablist] Critical pitfall of spectral power analysis?

Indeed, thanks for elaborating.

Even if they were different mechanisms, relating to different aspects of E/I balance, they would undoubtedly influence each other to an extent that would make it difficult to separate them in the inference process following a top-down analysis.

And then, extrapolating to limits, we have a continuum, at infinitely long time scales everything is periodic, and at very low time scales, we have spikes, which are instantaneous amplitude variations :)

On Tue, 2 Sept 2025 at 17:07, Gyurkovics, Mate <mategy at illinois.edu<mailto:mategy at illinois.edu>> wrote:
Hi Daniele,

some really interesting questions.

If we say that 1/f activity has some neuronal origin, and if we connect it to E/I balance (the two things could even be collapsed at least if we consider scalp EEG, since E/I balance is basically how generically deep we can go with our inference from scalp recordings), then it's difficult to think that E/I balance is not involved in oscillatory activity as well.

I actually agree with this point, and it's something I struggle with conceptually a bit, at least for scalp recordings. Oscillations are quite explicitly linked to E:I balance, at least in the sense that they are meant to emerge (to oversimplify this a bit) from the interplay of inhibitory and excitatory neurons, and represent excitation and inhibition reciprocally controlling the other. However, I think the key difference here is that this happens over time in a predictable fashion (inhibition goes up, excitation goes down, then excitation goes up, inhibition goes down, etc.). The E:I balance framework of broadband activity is more about the relative contribution of excitatory and inhibitory post-synaptic potentials to the signal we are measuring in a given moment (well, across a temporal integration window of course).

This is all touched upon this paper by Voytek & Knight: https://urldefense.com/v3/__https://www.sciencedirect.com/science/article/pii/S0006322315003546__;!!Mih3wA!B2t-7ddUbDo4auGfdTSpLbP0pke5LJFmwuhG-rcEBQ2UqHHx7LNa67gJlqwmXS04daNnlttThLiUsy2Whnh_rWTu$ <https://urldefense.com/v3/__https://www.sciencedirect.com/science/article/pii/S0006322315003546__;!!DZ3fjg!5mRrmD1_ruqUUXvZxTZDNjCuUFnBdb6yVatATW6I7FB_m55dRSEuN5Onqsv9RhW6G3QaH7MnaRWkz9NC76Nz6jWjoh8x$> - however, I'm not sure how exactly their logic generalises to scalp recordings, plus it's quite complex and I'd hate to misrepresent it. But very briefly, if I remember the argument correctly, it links 1/f shape more to spiking properties (neuronal outputs), whereas oscillations to resultant changes in the electrical field (which may or may not oscillate at the same freq that neurons are spiking at). They do simply state: "This broadband 1/f is different from an oscillation (71<https://urldefense.com/v3/__https://www.sciencedirect.com/science/article/pii/S0006322315003546*bib71__;Iw!!DZ3fjg!5mRrmD1_ruqUUXvZxTZDNjCuUFnBdb6yVatATW6I7FB_m55dRSEuN5Onqsv9RhW6G3QaH7MnaRWkz9NC76Nz6opxeEbu$>), which are narrowband spectral processes within the PSD (70<https://urldefense.com/v3/__https://www.sciencedirect.com/science/article/pii/S0006322315003546*bib70__;Iw!!DZ3fjg!5mRrmD1_ruqUUXvZxTZDNjCuUFnBdb6yVatATW6I7FB_m55dRSEuN5Onqsv9RhW6G3QaH7MnaRWkz9NC76Nz6kH_oexb$>) and which may have a separate neurophysiological mechanism from spiking activity."

Top-down modelling approaches ([...]), usually start from the assumption that 1/f and     broadband must be different things.

You mean 1/f and narrowband, right? Yes, I have the same impression that that is the prevailing sentiment. I think this also brings us full circle - the question really is whether this is correct or not, and if yes, then division (which is inherent in dB conversion too) may not be an ideal solution for baselining.

Thanks,
Mate


________________________________
Feladó: Daniele Marinazzo <daniele.marinazzo at gmail.com<mailto:daniele.marinazzo at gmail.com>>
Elküldve: 2025. szeptember 2., kedd 12:16
Címzett: Gyurkovics, Mate <mategy at illinois.edu<mailto:mategy at illinois.edu>>
Másolatot kap: EEGLAB List <eeglablist at sccn.ucsd.edu<mailto:eeglablist at sccn.ucsd.edu>>
Tárgy: Re: [Eeglablist] Critical pitfall of spectral power analysis?

Dear Mate, dear all,
thanks a lot for continuing this interesting discussion.
Regarding the independence of the mechanisms generating 1/f and oscillatory activity, what would these mechanisms be?
If we say that 1/f activity has some neuronal origin, and if we connect it to E/I balance (the two things could even be collapsed at least if we consider scalp EEG, since E/I balance is basically how generically deep we can go with our inference from scalp recordings), then it's difficult to think that E/I balance is not involved in oscillatory activity as well.
Top-down modelling approaches (not just Donoghue et al., but also early works such as this one from 1987 https://urldefense.com/v3/__https://www.tandfonline.com/doi/epdf/10.3109/00207458808985730__;!!Mih3wA!B2t-7ddUbDo4auGfdTSpLbP0pke5LJFmwuhG-rcEBQ2UqHHx7LNa67gJlqwmXS04daNnlttThLiUsy2WhuexuME5$ <https://urldefense.com/v3/__https://www.tandfonline.com/doi/epdf/10.3109/00207458808985730__;!!DZ3fjg!4yzUWnNeatKBGE830z91fv-3XQOdXg9yENuPX6-EvSNasxuaO0hvTO49HTv0xWpVb-GWm5igQrszkn-a_lgDAgGznI7O$>), usually start from the assumption that 1/f and broadband must be different things. I see how this can be sort of epistemologically inevitable, even though there are instances in which a parsimonious model explaining both has been proposed (https://urldefense.com/v3/__https://journals.plos.org/ploscompbiol/article?id=10.1371*journal.pcbi.1010012__;Lw!!Mih3wA!B2t-7ddUbDo4auGfdTSpLbP0pke5LJFmwuhG-rcEBQ2UqHHx7LNa67gJlqwmXS04daNnlttThLiUsy2WhhHIkujE$ <https://urldefense.com/v3/__https://journals.plos.org/ploscompbiol/article?id=10.1371*journal.pcbi.1010012__;Lw!!DZ3fjg!4yzUWnNeatKBGE830z91fv-3XQOdXg9yENuPX6-EvSNasxuaO0hvTO49HTv0xWpVb-GWm5igQrszkn-a_lgDAm-R5AO4$>).

On Mon, 1 Sept 2025 at 23:18, Gyurkovics, Mate via eeglablist <eeglablist at sccn.ucsd.edu<mailto:eeglablist at sccn.ucsd.edu>> wrote:
Thanks again for all the interesting points. I'm certianly learning a lot on the physics side - and also about the PSD in different animals, I was genuinely unaware of all this, but sounds super interesting.

I think the mechanism you are referring to, Makoto, is what's usually just described as "dendritic filtering", is it not? I'm aware of this process plus the low-pass filtering that happens as a consequence of spatial summation. These are the two main ones I was thinking of, so you are right, it was very imprecise on my part to talk about the low-pass filtering properties of the tissue.

As demonstrated in a classical study by Lopes da Silva and van
Leeuwen (1977), alpha oscillation is generated within the cortex which is
only 4-5 mm thick.

Just out of curiosity, what point was this sentence supporting?

I'm very happy to learn the conceptual distinction between trivial and
non-trivial contributions to the changes of 1/f power distribution. Thank
you Mate. Your works are impressive.

Very nice of you to say this, Makoto - I would, however, also like to stress that this particular distinction just reflects how I personally think about this problem (i.e., the contribution of the ERP to the spectrum), I'm sure reasonable people could disagree. (Although this is basically the logic we published in the Journal of Neuroscience paper linked above.)

@Eugen - you raise many interesting points. (I certainly agree that in scalp recordings at leat, oscillatory activity is sparse, and most robustly occurs when the brain is not engaged with a task, in the form of alpha activity, but that is about as bold as I can be here.)

is sinusoidal (with sharp peaks in the spectrum) activity and broadband (not necessarily 1/f) activity generated by different mechanisms?

I think, to put it very simply, this is one of the fundamental questions underlying this discussion here. If they are separate AND fairly independent, that is when the conclusions of our paper hold. If they are separate but interact, our conclusions will sometimes hold, other times maybe not. If they reflect the same underlying mechanism, our conclusions would likely rarely be a concern. I personally think that they likely reflect mechanisms that are separate at least to some extent - plus 1/f-like broadban activity likely reflects several, not just one, generative mechanisms as highlighted by Makoto and others here too.

Moreover, the function 1/f may simply be the result of the Fourier transform of a single excitatory or inhibitory postsynaptic potential.

As far as I recall, this point is covered in Gao et al. (2017), the paper that first linked 1/f-like features to excitation/inhibition balance.

Thanks,
Mate








________________________________
Feladó: Евгений Машеров <emasherov at yandex.ru<mailto:emasherov at yandex.ru>>
Elküldve: 2025. augusztus 30., szombat 9:07
Címzett: Gyurkovics, Mate <mategy at illinois.edu<mailto:mategy at illinois.edu>>
Másolatot kap: EEGLAB List <eeglablist at sccn.ucsd.edu<mailto:eeglablist at sccn.ucsd.edu>>; Wirsing, Karlton <kwirsing at vt.edu<mailto:kwirsing at vt.edu>>; Cedric Cannard <ccannard at protonmail.com<mailto:ccannard at protonmail.com>>; 장진원 <jinwon06292 at gmail.com<mailto:jinwon06292 at gmail.com>>; Makoto Miyakoshi <mmiyakoshi at ucsd.edu<mailto:mmiyakoshi at ucsd.edu>>
Tárgy: Re: [Eeglablist] Critical pitfall of spectral power analysis?

As a (naive and insufficiently substantiated hypothesis) — is sinusoidal (with sharp peaks in the spectrum) activity and broadband (not necessarily 1/f) activity generated by different mechanisms? Moreover, sinusoidal activity is a manifestation not of action, but of inaction of the brain. Physiological (alpha rhythm when closing the eyes, possibly also mu rhythm in the absence of proprioceptive signals, sleep spindles) or pathological (alpha coma and low-frequency sinusoids in the delta or theta ranges). It can be associated with the regulation of the level of constant potential and, in general, with metabolic processes carried out by the integral regulator generating oscillations (but we see oscillations directly only as an idle rhythm). Broadband activity seems to be directly associated with the functioning of individual neurons. Moreover, the function 1/f may simply be the result of the Fourier transform of a single excitatory or inhibitory postsynaptic potential. These mechanisms are interconnected, but different. Perhaps the mathematical apparatus for their study should also be different.

Your truly

Eugen Masherov,
Burdenko Neurosurgery Institute

> Thanks again everyone, for these very interesting points.
>
> Just to add to something that was said recently - yes, 1/f (or rather, 1/f^x) features are quite ubiquitous, I think practically any time series with some amount of autocorrelation will have a similar shape: https://urldefense.com/v3/__https://www.cell.com/trends/cognitive-sciences/fulltext/S1364-6613(14)00085-0__;!!Mih3wA!E0DB3LnNc6JHuXWc3N5M5iAUeusaX8LTN3dqbu9ZUeyzmDOwf3GVazliJU65YVxC6mC4VLMvHBOlkHKz4AeGoXXj$ - its ubiquity is covered nicely in this lovely paper, as far as I remember.
>
> I also get most of Makoto's points about how just the location of the neuronal inputs, either in terms of proximity to the soma or in terms of cortical layers, will affect the strength of the low-pass filtering, and thus the shape of the 1/f scaling. This is super interesting, and this and dendritic filtering are certainly discussed in the literature to some extent. I am a bit more sceptical whether such subtle differences could contribute to 1/f changes in scalp recordings, but Makoto suggests they could and I trust his expertise.
>
> If you perform an ERP task, it would change 1/f power distribution, not surprisingly, because task-triggered cortico-cortical and thalamo-cortical inputs are recruited.
>
> This is a very interesting point. In our 2021 paper linked above, we also make the point that 1/f shape should change in an event-related design, but for a more trivial reason: ERPs are non-oscillatory (in the simple sense that they are transient bursts that do not repeat with a clear period), and will thus have a 1/f shape in the frequency domain (indeed, they do, there are some figures in the paper). Thus, 1/f scaling will change after an event trivially because there are well-known non-band-limited changes happening in the EEG (the ERPs). We tried to correct for the contribution of the ERPs and still found post-stimulus 1/f changes that we consider non-trivial (a steepening to be specific). These, then, could be explained by the mechanism that Makoto suggests (which we did not consider in the paper, as it seemed maybe a bit small-scale to explain scalp-derived effects) and/or by Gao et al.'s excitation-inhibition balance idea (this is the framework we used in the paper). It certainly cannot be explained by the general low-pass filtering properties of the tissue or similar more or less fixed variables, as those should not change so rapidly.
>
> I share much of your scepticism about oscillatory mechanisms (in scalp recordings), Makoto, but if we take the most typical generative mechanisms assigned to these phenomena (interplay of pyramidal cells and interneurons), they seem like they could potentially interact with these other mechanisms described above, or be fairly independent.
>
> So we've got this really complex picture, where there could be oscillations going on (maybe in alpha only), there could be (independent?) 1/f dynamics happening for multiple reasons, e.g., because of the location and/or the nature (E vs. I) of neuronal inputs changing, and there could be ERPs happening too, which might partly be phase-locked oscillations, and could also be related to where the neuronal inputs are located, so they "straddle" these different mechanisms quite a bit, probably. Not too sure about the ERPs to be honest.
>
> Two more minor points:
>
> I can't put up with the fuzziness of how the term 'oscillation' is used in the field now. Is a try-phasic burst, such as a classical event-related N1-P1 waveform, an oscillation?
>
> I agree completely that it is very unclear what constitutes an oscillation - basically, how many cycles are enough for something to be considered an oscillation, and how do we show that those cycles come from the same generative mechanism, and not just multiple successive events happening. This is less of a question for longer, more stable oscillations, e.g., alpha at rest.
>
> And as for Michael's question: my limited experience with this topic would certainly suggest that 1/f dynamics (for whatever reason) could change very rapidly, and often in a systematic fashion (e.g., predictably after a stimulus). They also do seem to change on much slower time scales as well, e.g., across the lifespan.
>
> Thanks,
> Mate
>
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