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Transcranial alternating current stimulation modulates the perception of bistable apparent motion
Symposia Abstracts / International Journal of Psychophysiology 85 (2012) 291–360
large number of studies exploring the functional role of brain oscillations. Systematic modulations of oscillatory amplitude have been shown to relate to many cognitive processes including attention, memory and conscious perception. However, there has been little evidence that brain oscillations are causally involved in these processes. Recently, in an attempt to address this question researchers have used rhythmic external stimulations (either sensory, electric or magnetic) to modulate brain oscillations and observe possible behavioral consequences of this neuromodulatory approach. In a recent review (Thut et al…, Front. Perc. Sci 2011) we tried to summarize recent developments in the field, understand possible effects of rhythmic stimulation by looking at simulations inspired from Dynamic System Theory and suggest criteria for the identification of a successful modulation of ongoing brain oscillations. Rhythmic stimulation of the oscillating neural population can be modeled as periodic force acting in a certain direction on phase vector. In simulations this will lead to a synchronization of the oscillator to the external force, i.e. an entrainment of the oscillator by the force. This synchronization is characterized by a phase alignment of oscillator to the periodic force. However, in real MEG/EEG recordings the identification of entrainment is more complicated. It can be difficult to distinguish a phase entrainment of an ongoing oscillation from other possible scenarios giving rise to the same observations. In particular, a competing model posits that short rhythmic stimuli evoke transient components (with spectral characteristics similar to the ongoing oscillation) that add to the ongoing (oscillatory) activity. To identify entrainment in real data we propose to seek evidence along the following dimensions: (1) Synchronization of brain oscillations to the rhythmic stream of external events, as measured with EEG/MEG. (2) Frequency-specificity of entrainment effects in EEG/ MEG-signals, meaning that stimulation is maximally effective when corresponding to the natural frequency of the stimulated generator. (3) Spatial specificity of entrainment effects in EEG/MEG-signals, meaning that an oscillatory signature with distinct topography involving the target area is emerging from entrainment. (4) The targeted area can also cycle at the entrainment frequency in the absence of rhythmic stimulation (natural oscillator). (5) Frequency-specific behavioral consequences during rhythmic stimulation. (6) A cycling pattern of behavior during rhythmic stimulation. In applying these criteria to existing studies we conclude that there is reasonably strong evidence for the entrainment model. Still, further discussion in the community is needed and these (or similar) criteria need to be applied more widely to improve our understanding under what circumstances brain oscillations can be entrained with subsequent behavioral consequences. doi:10.1016/j.ijpsycho.2012.06.017
295
stimulation duration range of about 10 min tDCS allows for excitability increase and decrease, tACS and tRNS induce excitability increases in particular with higher frequencies between 100 and 600 Hz or in the low kHz range. TACS and tRNS induce less skin sensation than tDCS and accordingly can be blinded better. They are also no longer current flow direction sensitive as a main advantage when compared to tDCS. doi:10.1016/j.ijpsycho.2012.06.018
Transcranial alternating current stimulation modulates the perception of bistable apparent motion D. Strübera,b, S. Racha, S.A. Trautmann-Lengsfelda,c, A.K. Engelc, Christoph S. Herrmanna,b a Department of Experimental Psychology, Carl von Ossietzky Universität Oldenburg, Germany b Research Center Neurosensory Science, Carl von Ossietzky Universität Oldenburg, Germany c Department of Neurophysiology and Pathophysiology, University Medical Center Hamburg-Eppendorf, Germany 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, human electroencephalographic (EEG) studies demonstrated gamma band modulations during ambiguous perception. We have used 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. To establish a causal role of gamma band coupling in bistable motion perception, we applied transcranial alternating current stimulation (tACS) in the gamma range (40 Hz) over motion sensitive areas of both hemispheres and found an increase of interhemispheric gamma band coherence together with a decreased proportion of perceived horizontal motion. Given that bilateral tACS induces sinusoidal currents with 180° phase difference between hemispheres, the resulting interhemispheric functional decoupling leads to a relative decrease of horizontal motion perception. These findings demonstrate a direct relationship between gamma band coupling and conscious perception including both behavioral and electrophysiological evidence. doi:10.1016/j.ijpsycho.2012.06.019
Physiology of tACS W. Paulus Department of Clinical Neurophysiology, University of Göttingen, Germany
Evidence for entrainment of perceptually relevant brain rhythms by rhythmic TMS
Transcranial electric stimulation techniques have been developed as cheap and efficient tools for modifying cortical plasticity. Weak transcranial direct current stimulation (tDCS) induces plastic aftereffects via membrane polarization: cathodal stimulation hyperpolarizes, while anodal stimulation depolarizes the resting membrane potential, whereby the induced after-effects depend on polarity, duration and intensity of the stimulation. Transcranial alternating current (tACS) (Antal et al., 2008) and random noise stimulation (tRNS) intend to interfere with ongoing cortical oscillations (Terney et al., 2008). Using these techniques, we can induce and modify differently neuroplastic changes with different advantages and disadvantages of tDCS, tACS and tRNS. Plastic after-effects need a minimal stimulation duration time and may reverse with too long stimulation. Whereas in the normal
G. Thut, J. Gross University of Glasgow, Scotland, UK Neuronal elements functionally assemble through synchronization in distinct frequency bands, giving rise to brain rhythms that can be measured by electroencephalography (EEG). Transcranial magnetic stimulation (TMS) can be used to stimulate neuronal elements in rhythmic pulse-trains, at frequencies that characterize EEG-signals. This raises the questions whether frequency-tuned TMS could be used to directly interact with neuronal activity at the level of biologically relevant brain rhythms, what the underlying mechanisms of action are, and whether this may result in behavioural consequences. This talk is structured in 3 parts: 1) It will provide a short overview of what is
large number of studies exploring the functional role of brain oscillations. Systematic modulations of oscillatory amplitude have been shown to relate to many cognitive processes including attention, memory and conscious perception. However, there has been little evidence that brain oscillations are causally involved in these processes. Recently, in an attempt to address this question researchers have used rhythmic external stimulations (either sensory, electric or magnetic) to modulate brain oscillations and observe possible behavioral consequences of this neuromodulatory approach. In a recent review (Thut et al…, Front. Perc. Sci 2011) we tried to summarize recent developments in the field, understand possible effects of rhythmic stimulation by looking at simulations inspired from Dynamic System Theory and suggest criteria for the identification of a successful modulation of ongoing brain oscillations. Rhythmic stimulation of the oscillating neural population can be modeled as periodic force acting in a certain direction on phase vector. In simulations this will lead to a synchronization of the oscillator to the external force, i.e. an entrainment of the oscillator by the force. This synchronization is characterized by a phase alignment of oscillator to the periodic force. However, in real MEG/EEG recordings the identification of entrainment is more complicated. It can be difficult to distinguish a phase entrainment of an ongoing oscillation from other possible scenarios giving rise to the same observations. In particular, a competing model posits that short rhythmic stimuli evoke transient components (with spectral characteristics similar to the ongoing oscillation) that add to the ongoing (oscillatory) activity. To identify entrainment in real data we propose to seek evidence along the following dimensions: (1) Synchronization of brain oscillations to the rhythmic stream of external events, as measured with EEG/MEG. (2) Frequency-specificity of entrainment effects in EEG/ MEG-signals, meaning that stimulation is maximally effective when corresponding to the natural frequency of the stimulated generator. (3) Spatial specificity of entrainment effects in EEG/MEG-signals, meaning that an oscillatory signature with distinct topography involving the target area is emerging from entrainment. (4) The targeted area can also cycle at the entrainment frequency in the absence of rhythmic stimulation (natural oscillator). (5) Frequency-specific behavioral consequences during rhythmic stimulation. (6) A cycling pattern of behavior during rhythmic stimulation. In applying these criteria to existing studies we conclude that there is reasonably strong evidence for the entrainment model. Still, further discussion in the community is needed and these (or similar) criteria need to be applied more widely to improve our understanding under what circumstances brain oscillations can be entrained with subsequent behavioral consequences. doi:10.1016/j.ijpsycho.2012.06.017
295
stimulation duration range of about 10 min tDCS allows for excitability increase and decrease, tACS and tRNS induce excitability increases in particular with higher frequencies between 100 and 600 Hz or in the low kHz range. TACS and tRNS induce less skin sensation than tDCS and accordingly can be blinded better. They are also no longer current flow direction sensitive as a main advantage when compared to tDCS. doi:10.1016/j.ijpsycho.2012.06.018
Transcranial alternating current stimulation modulates the perception of bistable apparent motion D. Strübera,b, S. Racha, S.A. Trautmann-Lengsfelda,c, A.K. Engelc, Christoph S. Herrmanna,b a Department of Experimental Psychology, Carl von Ossietzky Universität Oldenburg, Germany b Research Center Neurosensory Science, Carl von Ossietzky Universität Oldenburg, Germany c Department of Neurophysiology and Pathophysiology, University Medical Center Hamburg-Eppendorf, Germany 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, human electroencephalographic (EEG) studies demonstrated gamma band modulations during ambiguous perception. We have used 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. To establish a causal role of gamma band coupling in bistable motion perception, we applied transcranial alternating current stimulation (tACS) in the gamma range (40 Hz) over motion sensitive areas of both hemispheres and found an increase of interhemispheric gamma band coherence together with a decreased proportion of perceived horizontal motion. Given that bilateral tACS induces sinusoidal currents with 180° phase difference between hemispheres, the resulting interhemispheric functional decoupling leads to a relative decrease of horizontal motion perception. These findings demonstrate a direct relationship between gamma band coupling and conscious perception including both behavioral and electrophysiological evidence. doi:10.1016/j.ijpsycho.2012.06.019
Physiology of tACS W. Paulus Department of Clinical Neurophysiology, University of Göttingen, Germany
Evidence for entrainment of perceptually relevant brain rhythms by rhythmic TMS
Transcranial electric stimulation techniques have been developed as cheap and efficient tools for modifying cortical plasticity. Weak transcranial direct current stimulation (tDCS) induces plastic aftereffects via membrane polarization: cathodal stimulation hyperpolarizes, while anodal stimulation depolarizes the resting membrane potential, whereby the induced after-effects depend on polarity, duration and intensity of the stimulation. Transcranial alternating current (tACS) (Antal et al., 2008) and random noise stimulation (tRNS) intend to interfere with ongoing cortical oscillations (Terney et al., 2008). Using these techniques, we can induce and modify differently neuroplastic changes with different advantages and disadvantages of tDCS, tACS and tRNS. Plastic after-effects need a minimal stimulation duration time and may reverse with too long stimulation. Whereas in the normal
G. Thut, J. Gross University of Glasgow, Scotland, UK Neuronal elements functionally assemble through synchronization in distinct frequency bands, giving rise to brain rhythms that can be measured by electroencephalography (EEG). Transcranial magnetic stimulation (TMS) can be used to stimulate neuronal elements in rhythmic pulse-trains, at frequencies that characterize EEG-signals. This raises the questions whether frequency-tuned TMS could be used to directly interact with neuronal activity at the level of biologically relevant brain rhythms, what the underlying mechanisms of action are, and whether this may result in behavioural consequences. This talk is structured in 3 parts: 1) It will provide a short overview of what is