[FieldTrip] some general questions about gamma-related analyses

[Ivaylo Iotchev]

For a second time, a heartfelt thank you!

Ivaylo Iotchev, PhD

Am Fr., 11. Nov. 2022 um 10:39 Uhr schrieb Tzvetan Popov <
tzvetan.popov at uni-konstanz.de>:

> Dear Ivo,
>
> The whole of the gamma range expands well beyond 30 Hz, the noise
> threshold, and thus the first question is whether low-pass filtering below
> 30 Hz is at all applied when looking for gamma coherence, power etc. ...
> One reason I kept the classical filter settings at first is to be
> consistent across the many different analyses I apply to the same data
> sets, not all of which have to do with gamma, but it dawned on me that
> filtering out frequencies above 30 is probably not a good idea(?) for
> gamma-related questions?
>
> No, do not apply 30Hz LP. You filter out your signal of interest.
>
>
> Moreover, is it acceptable to look for the point of maximum coherence
> within that range, rather than average within the range? The data suggests
> that the point of maximum coherence shifts across time to higher and higher
> frequencies, thus I decided for the time being to report the maximum
> coherence (across electrodes) value within the gamma range.
>
> One typically applies smoothening in the frequency domain when evaluating
> gamma (power and coherence). I suggest to study this lecture
> https://www.youtube.com/watch?v=dHTuzMsjVJA. In particular, at minute
> 25:49 the advantage of the freq smoothening is highlighted. Given that
> example your peak frequency will change depending on your decision how much
> to smooth.
>
> Of note, channel level coherence, particularly for gamma is not
> recommended. A lot of other stuff is added to the mix (e.g. cardiac, neck
> muscles etc.). Their contribution will change over time in your experiment.
> At the end you will not be able to interpret the results and/or you might
> be fooled.
> I suggest you also study this lecture
> https://www.youtube.com/watch?v=ZBwh0Vm4fh4 and in particular the issues
> raised from minute 42:49 or so.
>
> Good luck
> Tzvetan
>
>
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