Antiphasic 40 Hz Oscillatory Current Stimulation Affects Bistable Motion Perception

Abstract

When viewing ambiguous stimuli, conscious perception alternates spontaneously between competing interpretations of physically unchanged stimulus information. As one possible neural mechanism underlying the perceptual switches, it has been suggested that neurons dynamically change their pattern of synchronized oscillatory activity in the gamma band (30-80 Hz). In support of this hypothesis, there is correlative evidence from human electroencephalographic (EEG) studies for gamma band modulations during ambiguous perception. To establish a causal role of gamma band oscillations in the current study, we applied transcranial alternating current stimulation (tACS) at 40 Hz over occipital-parietal areas of both hemispheres during the presentation of bistable apparent motion stimuli that can be perceived as moving either horizontally or vertically. In this paradigm, the switch between horizontal and vertical apparent motion is likely to involve a change in interhemispheric functional coupling. We examined gamma tACS effects on the durations of perceived horizontal and vertical motion as well as on interhemispheric EEG coherence and found a decreased proportion of perceived horizontal motion together with an increase of interhemispheric gamma band coherence. In a control experiment using 6 Hz tACS, we did not observe any stimulation effects on behavior or coherence. Furthermore, external stimulation at 40 Hz was only effective when applied with 180° phase difference between hemispheres (anti-phase), as compared to in-phase stimulation with 0° phase difference. These findings suggest that externally desynchronizing gamma oscillations between hemispheres impairs interhemispheric motion integration and in turn biases conscious experience of bistable apparent motion.

Theta response in schizophrenia is indifferent to perceptual illusion

“…Previous studies have found large similarities for theta activity during the perception of ambiguous and unambiguous figures (Ehm, et al, 2011;Nakatani & van Leeuwen, 2005;Strüber, et al, 2014), but differences of theta activity indicating increased top-down requirements for the perception of ambiguous in comparison to unambiguous figures have also been found . In this study, we did not directly compare the ambiguous and unambiguous task, because the switching rates differed between both tasks, which seem to be a requirement for comparability (Nakatani & van Leeuwen, 2005;Strüber, et al, 2000;Strüber, et al, 2001).…”

“…A more explicit way to reveal top-down influences on multistable perception was undertaken by investigating voluntary slowing and accelerating of the individual reversal rate (Strüber & Stadler, 1999), which modulated the reversal-related delta and gamma activity (Mathes, et al, 2006). A functional role for interhemispheric gamma-band coherence over parieto-occipital areas in bistable motion perception was recently demonstrated using transcranial alternating current stimulation (tACS, Helfrich et al, 2014;Strüber, Rach, Trautmann-Lengsfeld, Engel, & Herrmann, 2014). An increase of posterior beta amplitudes after the onset of an ambiguous stimulus occurred after a perceptual change (Yokota, Minami, Naruse, & Nakauchi, 2014), its suppression has been related to top-down mechanisms stabilizing a new percept (Kloosterman et al, 2014).…”

EEG oscillations: From correlation to causality

“…TACS has also been applied in the gamma frequency band in order to modulate perception of bistable motion (Strüber et al, 2014). It had previously been shown that this type of motion perception depends on changes of the interhemispheric coherence in this frequency band.…”

Gestalt perception is associated with reduced parietal beta oscillations

“…The local synchronization will be reflected in an amplitude increase of intracortically measured local field potentials or scalp EEG, while long-range synchronization would show up as an increase in oscillatory phase coupling between signals in two areas. Indeed, multiple studies point to the importance of a transient increase in gamma band power and coherence for global perception of hierarchical stimuli as well as for interhemispheric integration and illusory contour perception (Rose and Büchel, 2005;Rose et al, 2006;Strüber et al, 2013;Tallon-Baudry et al, 1996). In addition, there is accumulating evidence for the role of theta and beta phase synchrony in grouping and illusion perception, which may be mediating information exchange between higher and lower level areas (Hanslmayr et al, 2013;Hipp et al, 2011;Keil et al, 2014;Romei et al, 2011;Smith et al, 2006;Volberg et al, 2013).…”