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Posterior alpha activity is not phase-reset by visual stimuli.

ABSTRACT: There is currently a debate as to whether event-related potentials and fields measured by using electroencephalography or magnetoencephalography are generated by ongoing oscillatory activity becoming phase-reset in response to a given stimulus. We performed a magnetoencephalography study measuring brain activity in response to visual stimuli. Using a measure termed the phase-preservation index we investigated the phase of oscillatory alpha activity (8-13 Hz) before and after the stimulus. We found that in single trials the alpha oscillations after visual stimuli preserve their phase relationship with respect to the phase before the stimuli. This finding argues against phase-resetting of ongoing oscillations as being responsible for visually evoked responses. The event-related field can be explained primarily by stimulus-locked activity in the band that is absent before the stimulus. These findings suggest that different neuronal events are responsible for generating the ongoing oscillations and the visually evoked responses.

SUBMITTER: Mazaheri A

PROVIDER: S-EPMC1413767 | biostudies-literature | 2006 Feb

REPOSITORIES: biostudies-literature

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Posterior alpha activity is not phase-reset by visual stimuli.

Mazaheri Ali A Jensen Ole O

Proceedings of the National Academy of Sciences of the United States of America 20060210 8

There is currently a debate as to whether event-related potentials and fields measured by using electroencephalography or magnetoencephalography are generated by ongoing oscillatory activity becoming phase-reset in response to a given stimulus. We performed a magnetoencephalography study measuring brain activity in response to visual stimuli. Using a measure termed the phase-preservation index we investigated the phase of oscillatory alpha activity (8-13 Hz) before and after the stimulus. We fou ...[more]

PMID: 16473952

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Project description:Initiating an eye movement towards a suddenly appearing visual target is faster when an accessory auditory stimulus occurs in close spatiotemporal vicinity. Such facilitation of saccadic reaction time (SRT) is well-documented, but the exact neural mechanisms underlying the crossmodal effect remain to be elucidated. From EEG/MEG studies it has been hypothesized that coupled oscillatory activity in primary sensory cortices regulates multisensory processing. Specifically, it is assumed that the phase of an ongoing neural oscillation is shifted due to the occurrence of a sensory stimulus so that, across trials, phase values become highly consistent (phase reset). If one can identify the phase an oscillation is reset to, it is possible to predict when temporal windows of high and low excitability will occur. However, in behavioral experiments the pre-stimulus phase will be different on successive repetitions of the experimental trial, and average performance over many trials will show no signs of the modulation. Here we circumvent this problem by repeatedly presenting an auditory accessory stimulus followed by a visual target stimulus with a temporal delay varied in steps of 2 ms. Performing a discrete time series analysis on SRT as a function of the delay, we provide statistical evidence for the existence of distinct peak spectral components in the power spectrum. These frequencies, although varying across participants, fall within the beta and gamma range (20 to 40 Hz) of neural oscillatory activity observed in neurophysiological studies of multisensory integration. Some evidence for high-theta/alpha activity was found as well. Our results are consistent with the phase reset hypothesis and demonstrate that it is amenable to testing by purely psychophysical methods. Thus, any theory of multisensory processes that connects specific brain states with patterns of saccadic responses should be able to account for traces of oscillatory activity in observable behavior.

Dataset Information

Posterior alpha activity is not phase-reset by visual stimuli.

Publications

Posterior alpha activity is not phase-reset by visual stimuli.

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