The broadband-transient induced gamma-band response in scalp EEG reflects the execution of saccades.
The contraction of the extra-ocular muscles, during the execution of saccades, produces a strong electric potential in the EEG called the saccadic spike potential (SP). At the frequency spectrum, this SP manifests as a broadband response with most of its power at the gamma-band frequencies. Saccadic activity is known to follow a time-pattern of repression (at around 50-150 ms post stimulus) which is followed by a large increase in saccadic rate at around 200-300 ms post stimulus. Due to this temporal pattern relative to the stimulus, and to the appearance of a SP at each saccade, this increase in saccadic rate shows up after averaging as an increase in gamma-band activity at the time-range of 200-300 ms. Thus, the broadband-transient "induced gamma-band response" frequently reported in the EEG literature, is in fact a "gamma-imposter", due to ocular myographic activity, and not to neural activity. Previous findings regarding the scalp EEG broadband-transient induced gamma-band response, relating it to neural synchronization and to various cognitive functions should be reevaluated considering the systematic contamination by ocular activity.
Yuval-Greenberg
Shlomit
S
Department of Psychology, The Hebrew University of Jerusalem, Mount Scopus, 91905 Jerusalem, Israel. Shlomit.greenberg@mail.huji.ac.il
Deouell
Leon Y
LY
D001921:Brain / Q000502:physiology*; D004569:Electroencephalography; D053483:Eye Movement Measurements; D006801:Humans; D009801:Oculomotor Muscles / Q000378:metabolism*; D012438:Saccades / Q000502:physiology*; D012535:Scalp; D013997:Time Factors