Simultaneous EEG/fMRI Analysis of the Resonance Phenomena in Steady-State Visual Evoked Responses

Abstract

The stability of the steady-state visual evoked potentials (SSVEPs) across trials and subjects makes them a suitable tool for the investigation of the visual system. The reproducible pattern of the frequency characteristics of SSVEPs shows a global amplitude maximum around 10 Hz and additional local maxima around 20 and 40 Hz, which have been argued to represent resonant behavior of damped neuronal oscillators. Simultaneous electroencephalogram/functional magnetic resonance imaging (EEG/fMRI) measurement allows testing of the resonance hypothesis about the frequency-selective increases in SSVEP amplitudes in human subjects, because the total synaptic activity that is represented in the fMRI-Blood Oxygen Level Dependent (fMRI-BOLD) response would not increase but get synchronized at the resonance frequency. For this purpose, 40 healthy volunteers were visually stimulated with flickering light at systematically varying frequencies between 6 and 46 Hz, and the correlations between SSVEP amplitudes and the BOLD responses were computed. The SSVEP frequency characteristics of all subjects showed 3 frequency ranges with an amplitude maximum in each of them, which roughly correspond to alpha, beta and gamma bands of the EEG. The correlation maps between BOLD responses and SSVEP amplitude changes across the different stimulation frequencies within each frequency band showed no significant correlation in the alpha range, while significant correlations were obtained in the primary visual area for the beta and gamma bands. This non-linear relationship between the surface recorded SSVEP amplitudes and the BOLD responses of the visual cortex at stimulation frequencies around the alpha band supports the view that a resonance at the tuning frequency of the thalamo-cortical alpha oscillator in the visual system is responsible for the global amplitude maximum of the SSVEP around 10 Hz. Information gained from the SSVEP/fMRI analyses in the present study might be extrapolated to the EEG/fMRI analysis of the transient event-related potentials (ERPs) in terms of expecting more reliable and consistent correlations between EEG and fMRI responses, when the analyses are carried out on evoked or induced oscillations (spectral perturbations) in separate frequency bands instead of the time-domain ERP peaks.

Assisted closed-loop optimization of SSVEP-BCI efficiency

“…Sequential randomness of this order is confirmed with Z = −0.230 and p exact = 0.828 ( Wald–Wolfowitz runs test after Mdn split dichotomization). Our findings that in the 20–39 Hz range, lower flicker frequencies over all subjects (Figure 6A) evoke higher SSVEP magnitudes are in line with other studies which reported a global maximum SSVEP amplitude around 10 Hz with additional local maxima around 20, 40, and 80 Hz (Regan, 1989; Herrmann, 2001; Bayram et al, 2011). In our sample, we found that SSVEP frequency-response curves differed remarkably between subjects (Figure 6B) probably due to trait and state variabilities which justifies that they are determined in our experiment in the scanning phase for every subject individually.…”

A multimodal approach to analysis of steady state visually evoked potentials

“…These coordinates are within the standard variation for the location of the primary visual cortex (V1) reported to be located at approximately [9, '67, 5] [32]. This finding confirms identified SSVEP activations in previously published fMRI studies [20], [21], [31]. No significant activations were found in the mid and high SSVEP frequency bands ( Figure 2).…”

“…The analysis of the EEG activity alone showed the typical steady state oscillation responses ( Figure 1A and B), confirming previously published studies [20], [21], [31]. The power of the main SSVEP frequency was very small for the mid frequency band (16.7Hz) and almost non-existent for the high frequency band (26.67Hz).…”

“…Combined, therefore, EEG and fMRI provides excellent temporal and spatial resolution, and there is a growing interest in utilizing both modalities in the study of SSVEPs (see e.g. [20], [21]). However, traditional analysis approaches to EEG and fMRI differ fundamentally.…”

SSVEP signatures of binocular rivalry during simultaneous EEG and fMRI

“…Little work has been reported, to our knowledge, on the integration of frequency-tagging SSVEP methods with functional MRI, though initial efforts to more generally study SSVEPs using EEG-fMRI have been promising [24]. Further development of these techniques as applied to binocular rivalry could significantly improve our understanding of its neural mechanisms.…”