qEEGsupport.com » technical issues

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

Jay Gunkelman — Thu, 19 Jan 2012 19:50:11 +0000

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)

Three Sets of Data from the Same EEG

Jay Gunkelman — Mon, 01 Feb 2010 18:22:25 +0000

This is three sets of data from the same underlying EEG, all with varying coherence results, and with the weighted average showing the alpha hypercoherent pattern with better fidelity than any other for this data.

These results are from 300 seconds of linked ear EEG data, note the dominant slower alpha peak frontally…. And the raw coherence values of that linked ear data. The raw EEG file sample is also included, so you can see the waveforms these values are being drawn from.

Linked Ears

Raw Coherence Values of Linked Ear Data

Raw EEG

The same exact 300 seconds of EEG data, reprocessed now with the weighted average montage. Note the difference in spectra, and waveform!!! The temporal slower alpha is now seen as the source of that slower alpha content.

The alpha hypercoherence in the EEG is easily seen in this data, but not in the linked ears.

This shows that you need to find the EEG montage that shows the actual EEG data for your case first, and THEN calculate coherence.

Weighted Average Spectra

Weighted Average Waveform

Weighted Average Raw

The images below show the Spectral plot, coherence plot and raw EEGs. Just like the other montages did. The Cz coherences are so inflated with field effects they are at 0.8 across the full spectrum at some sites, obviously artifactually high.

Spectral Plot

Coherence Plot

Raw EEG

Technical Issues in qEEG

Jay Gunkelman — Mon, 02 Feb 2009 21:49:13 +0000

Three part video by Jay Gunkelman discussing Technical Issues in qEEG.

Technical Issues in qEEG Power point Presentation

Continue Reading to see parts 2 and 3.

Part 2 Discusses Z-Scores and Standard Deviations