[Eeglablist] How many electrodes tolerated for interpolation?

[Scott Makeig]

I would question the value of channel interpolation - except for making
smooth pictures of particular scalp distributions. Individual
electrode-signal-difference scalp channels are inherently vague measures
that sum electrical activities generated in many unrelated parts of cortex.
Scalp channel signals are not more deserving of attention than individual
radio-frequency channels in an fMRI system ...

 I do understand that (at least in the US) clinicians need to work in terms
that insurance companies will reimburse. But cortical source-resolved EEG
recording and analysis is technically quite feasible, as our work at SCCN
over the last 30 years has abundantly demonstrated -- and allows more exact
interpretation (and high statistical certainty) than scalp-level data
interpretation.

Scott Makeig

On Tue, Nov 18, 2025 at 9:41 AM 장진원 via eeglablist <eeglablist at sccn.ucsd.edu>
wrote:

> Thank for your kind reply. I understand it.
>
> Best Regards,
> Jinwon
>
> On Mon, Nov 17, 2025 at 7:23 PM fernandez luis via eeglablist <
> eeglablist at sccn.ucsd.edu> wrote:
>
> > > Hi Jinwon,
> > >
> > > Accurate EEG channel interpolation is methodologically feasible across
> a
> > broad spectrum of montage densities, including low-density configurations
> > such as 19- and 32-channel systems, intermediate-density arrays such as
> 64
> > channels, and high-density systems such as 128 channels. Importantly, the
> > methodological validity of interpolation does not primarily depend on the
> > absolute number of electrodes, but on the availability of non-artifacted
> > neighboring electrodes with adequate spatial distribution surrounding the
> > channel to be reconstructed.
> > >
> > >
> > > EEG interpolation is a spatial estimation procedure in which the signal
> > of an artifacted electrode is reconstructed using mathematically weighted
> > contributions from the nearest clean surrounding electrodes. Accordingly,
> > if the spatially adjacent electrodes are also artifacted, interpolation
> > becomes unreliable or methodologically inappropriate, because the
> > reconstruction process would be driven by distorted input data—violating
> > key assumptions underlying spherical spline interpolation,
> inverse-distance
> > weighting, and other spatial estimation algorithms.
> > >
> > >
> > > In low-density montages (e.g., 19 or 32 channels), interpolation
> remains
> > technically feasible; however, the reduced spatial sampling inherently
> > limits the anatomical precision and spatial granularity of the
> > reconstructed signal. Nevertheless, interpolation in these systems can
> > yield clinically acceptable results as long as the electrodes used as
> > sources for reconstruction are clean, stable, and sufficiently
> distributed
> > around the artifacted location.
> > >
> > >
> > > Intermediate-density systems such as 64-channel EEG offer improved
> > spatial resolution that allows more accurate reconstruction of missing
> > channels due to enhanced scalp coverage. High-density montages,
> > particularly 128-channel EEG systems, provide dense and homogeneous
> spatial
> > sampling, minimizing interpolation error and generating reconstructions
> > that are more physiologically plausible and quantitatively reliable. This
> > level of spatial resolution is advantageous for applications requiring
> > high-fidelity scalp mapping, microstate analysis, connectivity
> estimation,
> > and source localization.
> > >
> > >
> > > Despite differences in resolution across montage densities, a
> > fundamental methodological requirement remains invariant: interpolation
> > must be performed exclusively using clean, non-artifacted surrounding
> > electrodes. Reconstruction based on artifacted neighbors compromises the
> > physiological validity of the estimated signal and undermines the
> > mathematical assumptions intrinsic to spatial interpolation algorithms.
> > >
> > >
> > > Technical Comparison: Conventional vs. High-Density EEG Interpolation
> > >
> > >
> > > 1. Interpolation in conventional EEG (19–32 channels)
> > >
> > >
> > > Low-density EEG systems rely on sparse spatial sampling, which imposes
> > several methodological constraints:
> > >
> > >
> > > • Wide inter-electrode spacing
> > >
> > > • Higher vulnerability to local contamination
> > >
> > > • Reduced capacity to capture rapid spatial changes
> > >
> > > • Acceptable but limited reliability
> > >
> > >
> > > 2. Interpolation in high-density EEG (64–128 channels)
> > >
> > >
> > > High-density EEG (HD-EEG) significantly enhances the reliability of
> > interpolation due to:
> > >
> > >
> > > • Dense and homogeneous spatial sampling
> > >
> > > • Robustness to isolated corrupted channels
> > >
> > > • Improved modeling of spatial gradients
> > >
> > > • Near-physiological reconstruction in 128-channel systems
> > >
> > > Best
> > > Luis Fernandez, MSc
> > > Clinical Neuropsychologist
> > >
> >
> > > El 17 nov 2025, a las 20:41, 장진원 via eeglablist <
> > eeglablist at sccn.ucsd.edu> escribió:
> > >
> > > Hi all,
> > >
> > > I'm a clinical psychiatrist, so I am not really familiar with
> engineering
> > > concept of interpolation. I believe in high-density setting (128
> channel)
> > > interpolation of a few channels are acceptable, but what if more than
> 10
> > > bad channels in 64 channel setting? Is it tolerable or detrimental for
> > > maintenance of true signal?
> > >
> > > Best regards,
> > > Jinwon Chang
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-- 
Scott Makeig, Research Scientist and Director, Swartz Center for
Computational Neuroscience, Institute for Neural Computation, University of
California San Diego, La Jolla CA 92093-0559, http://sccn.ucsd.edu/~scott