eeg artifacting

Move up to modern de-artifacting

There is an on-going dispute regarding de-artifacting methods used in qEEG.  Though there are vested interests counseling against the use of modern techniques to remove artifact while leaving the underlying EEG intact, there are also those who have specialized in the area that can provide a detailed reply to the vested interests.  Just such a reply was posted recently in a commercial list server, and we got the author’s permission to re-post the discussion on the qEEGSupport.com website in a non-commercial publicly accessible form for all to see.

It specifically points to the fact that the phase changes seen are due to removal of artifact, not the distortion of the underlying EEG, which has residual subtle artifacts remaining if processed with classical approaches.

If you cut time segments out of the EEG to remove artifacts, you also remove the underlying connectivity information, splicing discontinuous microstates together destroys the underlying time series.

In the give and take of the real world of neuroscience, the need to provide a valid time-series showing the connectivity of the neural networks, yet free of artifact, is driving the need to switch to more modern techniques than snipping out segments of time.  If you want to distort the timeline of the EEG (phase) just cut and paste lots of EEG together in one second chunks.

The neuroscience community will undoubtedly continue to discuss these issues, but the need for clean valid EEG is driving the field to these newer techniques, and they are performing well under the scrutiny.

Jay Gunkelman

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Technical Details in EEG Diagnosis of Autism

Many have heard experts in the neurofeeback field state vehemently that the “ICA deartifacting ruins the EEG”, and that “remontaging to a Laplacian montage ruins coherence”. There are internet tutorials attempting to support these opinions. This self-publication on-line on a commercial site is not the same as peer review, and many publish bad opinions without an alternative approach even considered.

Rather than engage in the meaningless back and forth of mere opinions, I thought it was better to wait for the decision of the jury.. a jury of our peers inherent to the peer reviews in professional publications seen in the field of neuroscience. I comfortably accept the judgment of the field’s journal’s editors.

Harvard’s famous Electroencephalographer, Frank Duffy M.D. just published a large scale well designed study. Some of the key aspects in the paper are highlighted and discussed below:

“Remaining eye blink and eye movement artifacts, which may be surprisingly prominent even during the eyes closed state, were removed by utilizing the source component technique [42, 43] as implemented in the BESA (BESA GmbH, Freihamer Strasse 18, 82116 Gräfelfing Germany) software package”

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Coherence Models and artifacts – Prior published findings in Autism are artifactual.

The following link to the article “Movement during brain scans may lead to spurious patterns” contains peer reviewed hard evidence of a clear cut case of poor deartifacting and excessively short recording times combining to create artifactual findings… findings that had high reliability within the data set, but which had results which were determined by artifact (movement). Even bad data can be repeatable.

This paper brings into clear question the commonly taught model of short and long distance connectivity which has been taught as a “cortical-cortical connectivity” issue, when many have pointed to the logical fallacy to this theory seen in the International Federation of Clinical Neurophysiology position paper (Basic Mechanisms of Cerebral Rhythmic Activities) on EEG generators, which showed that cutting cortical-cortical connections did not alter coherence (making the theory false).

I have presented this to the people in the field in an effort to correct the “cortical-cortical connectivity” theory – that has been promoted.

I hope the two compartmental cortical-cortical connectivity theory will fade away, especially as publications like this and the IFCN position paper point in a different direction.

Jay

More Reading: Control of Spatiotemporal Coherence of a Thalamic Oscillation by Corticothalamic Feedback Science 1 November 1996:Vol. 274 no. 5288 pp. 771-774 DOI: 10.1126/science.274.5288.771

Movement during brain scans may lead to spurious patterns from Simons Foundation Autism Research Initiative (SFARI)

qEEG Artifacting

The qEEG represents the statistical manipulation of the raw EEG, so an understanding of these manipulations should precede any discussion of the qEEGs clinical indications for protocols. Without such knowledge any given finding may be misinterpreted.

Following the careful recording of the EEG, the quantitative analysis is begun with the sampling of the data to be used in the analysis by the Fourier transform. The Fourier analysis assumes there are no transients (epileptic discharges, episodic voltage changes etc.) or state changes (light sleep, drug effect, mental task, etc.), so these must be avoided when selecting data for analysis in qEEG for eyes closed resting database comparison. There are some eyes open and task databases available more recently (Hudspeth, Sterman, Duffy etc.)

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