Cross-frequency coupling of eye-movement related LFP activities of freely viewing monkeys

Quantifying Neural Oscillatory Synchronization: A Comparison between Spectral Coherence and Phase-Locking Value Approaches

“…An example of variation lost by trial averaging is the presence of effects induced by saccadic or microsaccadic eye movements during presentation of a stimulus. It is known that saccadic eye-movements strongly affect the oscillatory properties [ 29 , 71 , 99 , 100 ] in the ‘sustained part’ of the trial-averaged TFR of signals in visual cortex, and that these saccadic effects can be useful indicators of perceptual and cognitive states [ 101 ]. However, these TFR variations are not locked to stimulus onset, but to saccades which occur at various time points within a trial, and therefore these interesting single-trial TFR variations are removed by classical stimulus-onset triggered trial averaging.…”

“…Unfortunately, these critical assumptions are rarely tested in neuroscience studies and it is uncertain how often the violation of stationarity and linearity assumptions of the signal affects the reported coherence results. In addition, there is increasing evidence that neural oscillatory signals show properties of non-stationarity that make them almost by definition unsuited for analysis by spectral coherence methods [ 10 , 29 – 34 ].…”

On the operation of visual cortical gamma in the light of frequency variation

“…Further, in monkey S microsaccadetriggered coherence analysis (Fig. 2E) confirmed a microsaccade-dependent modulation of V1-V2 gamma coherence in frequency and strength (both p < 0.01) similar to theta-triggered coherence analysis in monkeys S and K. These results support the view that microsaccades play a critical role in theta-rhythmic gamma dynamics Ito et al, 2011). The microsaccade-triggered analysis revealed intricate structure in oscillatory activity that was hidden in commonly-used stimulus-onset triggered analysis (Fig.…”

“…Although we cannot be sure what the difference in the magnitude of coherence in alpha-beta range between monkeys is due to, we can assert it is unlikely to be due to task differences as the monkeys were only required to fixate. Previous studies have indicated that the theta rhythm is linked to (micro)saccades Ito et al, 2011;. Microsaccades are small, involuntary eye movements that occur during fixation.…”

“…A particular type of CFC represents the linkage between gamma oscillations and (often rhythmic) movements of sensory organs. For example, in the visual system, gamma modulations have been linked to saccadic eye movements (Rajkai et al, 2008;Ito et al, 2011;. CFC has been studied mainly in terms of phaseto-power interactions.…”