Abstract

Steady-state visual evoked potentials (SSVEPs), the brain response to visual flicker stimulation, have proven beneficial in both research and clinical applications. Despite the practical advantages of stimulation at high frequencies in terms of visual comfort and safety, high frequency-SSVEPs have not received enough attention and little is known about the mechanisms behind their generation and propagation in time and space. In this study, we investigated the origin and propagation of SSVEPs in the gamma frequency band (40–60 Hz) by studying the dynamic properties of EEG in 32 subjects. Using low-resolution brain electromagnetic tomography (sLORETA) we identified the cortical sources involved in SSVEP generation in that frequency range to be in the primary visual cortex, Brodmann areas 17, 18 and 19 with minor contribution from sources in central and frontal sites. We investigated the SSVEP propagation as measured on the scalp in the framework of the existing theories regarding the neurophysiological mechanism through which the SSVEP spreads through the cortex. We found a progressive phase shift from posterior parieto-occipital sites over the cortex with a phase velocity of approx. 8–14 m/s and wavelength of about 21 and 24 cm. The SSVEP spatial properties appear sensitive to input frequency with higher stimulation frequencies showing a faster propagation speed.

Highlights

  • Steady-state visual evoked potentials (SSVEPs), the brain response to visual flicker stimulation, have proven beneficial in both research and clinical applications

  • When Repetitive visual stimulation (RVS) is superimposed on a cognitive task, especially around the alpha frequency band (8–12 Hz), specific topographic changes in amplitude and phase of the SSVEP appear analogous to the site-specific reductions in alpha EEG amplitude associated with cognitive and motor t­ asks[3]

  • We set to investigate the SSVEP responses to periodic visual stimulation at high frequencies within the gamma band (40–60 Hz) by studying the dynamic properties of EEG measured by sparse electrode montage in 32 subjects

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Summary

Introduction

Steady-state visual evoked potentials (SSVEPs), the brain response to visual flicker stimulation, have proven beneficial in both research and clinical applications. Repetitive visual stimulation (RVS), or visual flicker, at a frequency in the range from 1 to 100 Hz elicits an oscillatory response in the electroencephalogram (EEG) at the same frequency and/or its harmonics known as steady-state visual evoked potentials (SSVEPs) This response is time and phase-locked to the driving stimulus. When RVS is superimposed on a cognitive task, especially around the alpha frequency band (8–12 Hz), specific topographic changes in amplitude and phase of the SSVEP appear analogous to the site-specific reductions in alpha EEG amplitude associated with cognitive and motor t­ asks[3] This technique is known as steady-state topography and has been applied for studying working m­ emory[3,4], binocular ­rivalry[5], selective ­attention6,7, ­vigilance[8] and even e­ motions[9]. SSVEPs are applied for the investigation and treatment monitoring of age-related

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