[FieldTrip] Baseline correction for coherence involving EMG signals

[Schoffelen, J.M. (Jan Mathijs)]

Dear Uri,

I think that here I agree with the ‘senior scientist’ and not with the ‘reviewer’. Although there is nothing particularly wrong with subtracting some noisy number from an estimate of coherence during isometric contraction, it is a bit like comparing apples with oranges. In the absence of motor-unit potentials in the EMG, there is no reason to expect that the coherence coefficient between the EMG and the STN actually reflects some meaningful coupling.

Better would be to design an experimental contrast, and compare conditions (while the properties of the univariate signals stay as similar as possible across conditions). For instance, as in

http://www.jneurosci.org/content/31/18/6750.long

If the whole motivation for doing a ‘baseline correction’ is to account for estimation bias due to the finite number of observations, you could estimate this bias by a shuffling procedure (shuffling the epochs for one of the signals, with respect to the other one before re-computing the coherence), or a parametric correction.


Best wishes,
Jan-Mathijs



J.M.Schoffelen, MD PhD
Associate PI, VIDI-fellow - PI, language in interaction
Telephone: +31-24-3614793
Physical location: room 00.028
Donders Centre for Cognitive Neuroimaging, Nijmegen, The Netherlands



On 14 May 2019, at 02:54, Uri Eduardo Ramírez Pasos <urieduardo at gmail.com<mailto:urieduardo at gmail.com>> wrote:

Dear fieldtrippers,

I'm wondering if there is any consensus regarding baseline correction for coherence when (at least) one of the signals is an EMG, where baseline is some period at rest before movement onset. At an MDS congress a senior scientist said to me that cortex-muscle coherence should not be baseline-corrected since the EMG during rest is just noise as opposed to representing ongoing processing that is irrelevant to the task at hand. However, recently a reviewer wrote that they didn't see anything wrong with this and I should actually baseline-correct STN-muscle coherence values.

Any useful references would also be appreciated!

Best,
Uri Ramírez

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