EEG Question

19/07/2009 by admin.

There has recently been discussion of how much the gamma signal is associated with neural activity and how much it is associated with movements of the eye muscles. Below is the abstract of a paper from Yuval-Greenberg’s group, ‘Transient induced gamma-band response in EEG as a manifestation of miniature saccades’.

“The induced gamma-band EEG response (iGBR) recorded on the scalp is widely assumed to reflect synchronous neural oscillation associated with object representation, attention, memory, and consciousness. The most commonly reported EEG iGBR is a broadband transient increase in power at the gamma range approximately 200-300 ms following stimulus onset. A conspicuous feature of this iGBR is the trial-to-trial poststimulus latency variability, which has been insufficiently addressed. Here, we show, using single-trial analysis of concomitant EEG and eye tracking, that this iGBR is tightly time locked to the onset of involuntary miniature eye movements and reflects a saccadic “spike potential.” The time course of the iGBR is related to an increase in the rate of saccades following a period of poststimulus saccadic inhibition. Thus, whereas neuronal gamma-band oscillations were shown conclusively with other methods, the broadband transient iGBR recorded by scalp EEG reflects properties of miniature saccade dynamics rather than neuronal oscillations.”

As far as I can tell, the question is not settled. There is no doubt that there is gamma voltages from neural processing, and there is no doubt that voltages are produced by muscles. Further it is not unreasonable to presume that saccade eye movements are synchronized with processes creating consciousness. What is not clear is what features of the EEG are from muscles or from neurons. A good review is a posting by Chris Chathan’s (here).

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