Stimulus Specificity of Phase-Locked and Non-Phase-Locked 40 Hz Visual Responses in Human

Abstract

Considerable interest has been raised by non-phase-locked episodes of synchronization in the gamma-band (30 -60 Hz). One of their putative roles in the visual modality is featurebinding. We tested the stimulus specificity of high-frequency oscillations in humans using three types of visual stimuli: two coherent stimuli (a Kanizsa and a real triangle) and a noncoherent stimulus ("no-triangle stimulus"). The task of the subject was to count the occurrences of a curved illusory triangle. A time-frequency analysis of single-trial EEG data recorded from eight human subjects was performed to characterize phaselocked as well as non-phase-locked high-frequency activities.We found an early phase-locked 40 Hz component, maximal at electrodes Cz-C4, which does not vary with stimulation type. We describe a second 40 Hz component, appearing around 280 msec, that is not phase-locked to stimulus onset. This component is stronger in response to a coherent triangle, whether real or illusory: it could reflect, therefore, a mechanism of feature binding based on high-frequency synchronization. Because both the illusory and the real triangle are more targetlike, it could also correspond to an oscillatory mechanism for testing the match between stimulus and target. At the same latencies, the low-frequency evoked response components phase-locked to stimulus onset behave differently, suggesting that low-and high-frequency activities have different functional roles.

Human face preference in gamma-frequency EEG activity

“…In order to verify that the activity seen during this time window is on an induced (rather than evoked) nature, we calculated the mean inter-trial phase locking values for each subject during this period (described by Tallon-Baudry et al, 1996;Delorme and Makeig, 2003). This measure produces a number between 0 and 1 reflecting the amount of phase locking between trials (1 -completely phase locked).…”

“…Changing the conception that physiologically pertinent EEG frequencies are lower than 20 Hz, studies in animals (Singer and Gray, 1995) and in humans (e.g. Tallon-Baudry et al, 1996, 2003Gruber et al 2004Gruber et al , 2005Rodriguez et al 1999) explored activity in a range of frequencies higher than 20 Hz, which were addressed as "gamma-band". Specifically, many studies have associated between high-level perceptual mechanisms and the so-called "induced" gamma-band activity (iGBA; for review see Bertrand and Tallon-Baudry, 2000).…”

“…The amplitude of these bursts is modulated by physical stimulus attributes such as size, contrast and spatial-frequency spectrum (Gray et al, 1990;Bauer et al, 1995, Busch et al, 2004, perceptual factors acting bottom-up, such as the ability to form coherent gestalts Tallon-Baudry et al, 1996), and top-down acting factors such as attention Tiitinien et al, 1993, Fan et al 2007 or memory (Osipova et al, 2006;Gruber and Müller 2006;Gruber et al, 2004;TallonBaudry et al, 1998, 2001, Jensen et al 2007. In concert, these bottom-up and top-down modulations raised the hypothesis that iGBA reflects the integration of sensory input with preexistent memory representations to form experienced entities (Tallon-Baudry 1997, 2003).…”

Intersubject variability and induced gamma in the visual cortex: DCM with empirical Bayes and neural fields

“…The functional significance of cortical gamma band activity speaks to several important issues: including its ability to coordinate communication among neural populations, for example, those involved in attending to a particular stimulus [Fries, 2009], binding input features to cortical representations [Buzsáki and Chrobak, 1995; Gray et al, 1989] and mediating information transfer [Lachaux et al, 2005; Tallon‐Baudry et al, 1996]. In particular, gamma activity has on the one hand been used to characterize functional connectivity in cortical networks, for example, [Cabral et al, 2011] and on the other to study aberrant dynamics associated with potential pathophysiology.…”

Modelling event-related responses in the brain

“…On the other hand, if interactions are prevalent, the difference should change with each realisation of ongoing activity. We performed these analyses with different levels of input and assessed the degree of phase-locking in the outputs with the phase-locking value (PLV) (Lachaux et al, 1999;Tallon-Baudry et al, 1996): PLV(t) = |hexp(j/(t))i trials | where the instantaneous phase /(t) was obtained from the Hilbert transform (Le Van Quyen et al, 2001). …”