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Kudo to Alexei !! 1) Dynamic Brain Sources of Visual Evoked Responses S. Makeig, et alAbstract:It has been long debated whether averaged electrical responses recorded from the scalp result from stimulus-evoked brain events or stimulus-induced changes in ongoing brain dynamics. In a human visual selective attention task, we show that nontarget event-related potentials were mainly generated by partial stimulus-induced phase resetting of multiple electroencephalographic processes.Independent component analysis applied to the single-trial data identified at least eight classes of contributing components, including those producing central and lateral posterior alpha, left and right mu, and frontal midline theta rhythms. Scalp topographies of these components were consistent with their generation in compact cortical domains. 2) The Relationship Between Prestimulus Alpha Amplitude and Visual Evoked Potential Amplitude by Brandt et al Root-mean-square (RMS) amplitude derived from power spectral measures in the alpha band of the 1 s prestimulus EEG were related to the peak-to-peak amplitude of the N1 and P2 components (NlP2PP) of the visual evoked potential (VEP) in 7 male subjects. Stimuli were low intensity flashes delivered randomly between 2 and 6 whole seconds. Trials were rank ordered according to the levels of prestimulus alpha amplitude and were partitioned into groups of 40 trials each (25 groups per data set). Averaged VEPs were computed from these groups and scattergrams of NlP2PP and enhancement factor (following the approach by BaSar, 1980) vs. prestimulus alpha amplitude were produced. There was a correlation of 0.74 ( p < .oOOl) between prestimulus alpha amplitude and NlP2PP, and all seven subjects displayed a general inverse relationship between VEP enhancement and prestimulus alpha amplitude, replicating the results of Bagar. However, we observed an exponential relationship, rather than the linear relationshipreported by BaSar. 3) The Visual Evoked Potential is independent of surface alpha rhythm phase by Risner et al A Visual Evoked Potential (VEP) is an electrical signal picked up by a surface electrode in response to the activation of visual cortex by a visual stimulus. Because the VEP is typically much smaller in magnitude than the ongoing spontaneous EEG signal, the VEP is derived by averaging a large number of responses timelocked to stimulus presentation. Standard theory has it that the VEP is independent of the ongoing EEG, however, there has long been a competing view that the VEP is caused by a partial phase reset of the spontaneous alpha rhythm. We calculated the VEP where stimuli were presented at four different phases of the ongoing alpha rhythm, and subtracted away the responses to null trials synchronized to the same alpha rhythm phases, creating estimates of the VEP as a function of ongoing alpha rhythm phase. For some subjects there was evidence of an interaction between the VEP and the phase of the ongoing alpha rhythm, but thiswas idiosyncratic between subjects and conditions, and mostly evident in a later period when the VEP magnitude was very small. However, in general the VEP is independent of the phase of the ongoing alpharhythm, and hence cannot be primarily caused by a partial phase resetting of the spontaneous EEG. It is possible that the VEP is either a phase-reset of an ongoing oscillation, or an oscillation induced by the sudden onset of a stimulus, but it cannot be the same oscillation as the surface alpha 4) Influence of ongoing alpha rhythm on the visual evoked potential by Robert Becker, Petra Ritter, and Arno Villringer Abstract:The relationship between ongoing occipital alpha rhythm (8–12 Hz)and the generation of visual evoked potentials (VEPs) has been discussed controversially. While the "evoked theory" sees no interaction between VEP generation and the alpha rhythm, the "oscillatory theory" (also known as "phase-reset theory") postulates VEP generation to be based on alpha rhythm phase resetting. Previous experimental results are contradictory, rendering a straightforward interpretation difficult. Our approach was to theoretically model the implications of the evoked and oscillatory theory also incorporating stimulus-induced alpha-rhythm desynchronization. As a result, the model based on the oscillatory theory predicts alpha-band dependent VEP amplitudes but constant phase locking. The model based on the evoked theory predicts unaffected VEP amplitudes but alpha-band dependent phase locking. Subsequently, we analyzed experimental data in which VEPs were assessed in an "eyes open" and "eyes closed" condition in 17 subjects. For early components of the VEP, findings are in agreement with the evoked theory, i.e. VEP amplitudes remain unaffected and phase locking decreases during periods of high alpha activity. Late VEP component amplitudes (N175 ms), however, are dependent on pre-stimulus alpha amplitudes. This interaction is contradictory to the oscillatory theory since this VEP amplitude difference is not paralleled by a corresponding difference in alphaband amplitude in the affected time window. In summary, by using a model-based approach we identified early VEPs to be compatible with the evoked theory, while results of late VEPs support a modulatory but not causative role – the latter implied by the oscillatory theory – of alpha activity for EP generation 5) To See or Not to See: Prestimulus alpha Phase Predicts Visual Awareness by Mathewson et al Abstract:We often fail to see something that at other times is readily detectable. Because the visual stimulus itself is unchanged, this variability in conscious awareness is likely related to changes in the brain. Here we show that the phase of EEG rhythm measured over posterior brain regions can reliably predict both subsequent visual detection and stimulus-elicited cortical activation levels in a metacontrast masking paradigm. When a visual target presentation coincides with the trough of alpha wave, cortical activation is suppressed as early as 100 ms after stimulus onset, and observers are less likely to detect the target. Thus, during one alpha cycle lasting 100 ms, the human brain goes through a rapid oscillation in excitability, which directly influences the probability that an environmental stimulus will reach conscious awareness. Moreover, ERPs to the appearance of a fixation cross before the target predict its detection, further suggesting that cortical excitability level may mediate target detection. A novel theory of cortical inhibition is proposed in which increased alpha power represents a "pulsed inhibition" of cortical activity that affects visual awareness. 6) Novel modes of rhythmic burst firing at cognitively-relevantfrequencies in thalamocortical neurons by Hughes et al Abstract:It is now widely accepted that certain types of cognitive functions are intimately related to synchronized neuronal oscillations at both low (α/θ) (4–7/8–13 Hz) and high (β/γ) (18–35/ 30–70 Hz) frequencies. The thalamus is a key participant in many of these oscillations, yet the cellular mechanisms by which this participation occurs are poorly understood. Here we describe how, under appropriate conditions, thalamocortical (TC) neurons from different nuclei can exhibit a wide array of largely unrecognised intrinsic oscillatory activities at a range of cognitively-relevant frequencies. For example, both metabotropic glutamate receptor (mGluR) and muscarinic Ach receptor (mAchR) activation can cause rhythmic bursting at α/θ frequencies. Interestingly, key differences exist between mGluR- and mAchR-induced bursting, with the former involving extensive dendritic Ca2+ electrogenesis and being mimicked by a non-specific block of K+ channels with Ba2+, whereas the latter appears to be more reliant on proximal Na+ channels and a prominent spike afterdepolarization (ADP). This likely relates to the differential somatodendritic distribution of mGluRs and mAChRs and may have important functional consequences. We also show here that in similarity to some neocortical neurons, inhibiting large-conductance Ca2+-activated K+ channels in TC neurons can lead to fast rhythmic bursting (FRB) at ∼40 Hz. This activity also appears to rely on a Na+ channel-dependent spike ADP and may occur in vivo during natural wakefulness. Taken together, these results show that TC neurons are considerably more flexible than generally thought and strongly endorse a role for the thalamus in promoting a range of cognitively-relevant brain rhythms.