imagcoherence.h File Reference

Volume-conduction-robust imaginary coherence (Nolte et al., 2004) between every channel pair. More...

#include "../connectivity_global.h"
#include "abstractmetric.h"
#include "../connectivitysettings.h"
#include <QSharedPointer>
#include <Eigen/Core>

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Classes
class	CONNECTIVITYLIB::ImagCoherence
	Imaginary-coherence estimator (Nolte et al. 2004); rejects zero-lag volume-conduction mixing. More...

Namespaces
namespace	CONNECTIVITYLIB
	Functional connectivity metrics (coherence, PLV, cross-correlation, etc.).

Detailed Description

Volume-conduction-robust imaginary coherence (Nolte et al., 2004) between every channel pair.

SPDX-License-Identifier: BSD-3-Clause Copyright (c) 2018-2026 MNE-CPP Authors

Author

Daniel Strohmeier danie.nosp@m.l.st.nosp@m.rohme.nosp@m.ier@.nosp@m.gmail.nosp@m..com; Lorenz Esch loren.nosp@m.z.es.nosp@m.ch@tu.nosp@m.-ilm.nosp@m.enau..nosp@m.de; Juan GPC jgarc.nosp@m.iapr.nosp@m.ieto@.nosp@m.mgh..nosp@m.harva.nosp@m.rd.e.nosp@m.du; Gabriel Motta gabri.nosp@m.elbe.nosp@m.nmott.nosp@m.a@gm.nosp@m.ail.c.nosp@m.om; Christoph Dinh chris.nosp@m.toph.nosp@m..dinh.nosp@m.@mne.nosp@m.-cpp..nosp@m.org

Since

0.1.0

Date

April 2018

Imaginary coherence is the imaginary part of complex coherency,

ImCoh_{xy}(f) = Im( S_{xy}(f) / sqrt(S_{xx}(f) * S_{yy}(f)) )

with output range [-1, 1] - or [0, 1] when reported as |Im(Coh)|, as done here. Its key property, established by Nolte, Bai, Wheaton, Mari, Vorbach and Hallett (NeuroImage 2004), is that any instantaneous mixing of independent sources (volume conduction, common-reference, common-pickup) projects purely onto the real axis and therefore contributes 0 to Im(Coh). Only interactions with a non-zero phase lag - the signature of finite conduction delay between two true neural generators - survive, which makes this estimator a standard choice for sensor-space MEG/EEG connectivity where volume conduction would otherwise dominate ordinary coherence.

The trade-off is reduced sensitivity to genuine but short-lag interactions and a non-trivial dependence on the relative source orientations, so ImCoh is usually reported alongside the phase-based estimators (PLI, wPLI) which share its anti-leakage property but have different bias/variance profiles.

Definition in file imagcoherence.h.