Human Cerebral Activation during Steady-State Visual-Evoked Responses

Abstract

Flicker stimuli of variable frequency (2-90 Hz) elicit a steady-state visual-evoked response (SSVER) in the electroencephalogram (EEG) with the same frequency as the stimulus. In humans, the amplitude of this response peaks at approximately 15 Hz, decreasing at higher stimulation frequencies. It was not known whether this peak response corresponds to increased synaptic activity in the visual cortex or to other mechanisms [for instance, the temporal coherence (phase summation) of evoked responses]. We studied the SSVER in 16 normal volunteers by means of visual stimulation at 14 different frequencies (from 5 to 60 Hz) while recording the EEG. In nine subjects of the group, we measured regional cerebral blood flow (rCBF) with positron emission tomography (PET)-H2(15)O at rest and during visual stimulation at five different frequencies: 5, 10, 15, 25, and 40 Hz. We confirmed that the amplitude of the SSVER in occipital regions peaks at 15 Hz stimulation. Applying to the PET rCBF data a contrast weighted by the amplitude of the SSVER, we determined that the primary visual cortex rCBF follows an activation pattern similar to the SSVER. This finding suggests that the amplitude of the SSVER corresponds to increased synaptic activity, specifically in Brodmann's area 17. Additionally, this study showed that visual stimulation at 40 Hz causes selective activation of the macular region of the visual cortex, and that a region in the dorsal aspect of the Crus I lobule of the left cerebellar hemisphere is activated during repetitive visual stimulation.

Neural correlates of perceptual filling-in of an artificial scotoma in humans

“…An artificial scotoma was created by placing a small flickering square achromatic target (1.12 by 1.12°) on the background in the lower left visual field at 9.43°eccentricity (8°across, 5°down) flickering between black (luminance 2.5 cd/m 2 ) and white (luminance 98.4 cd/m 2 ) at a rate of 7.5 Hz (eight screen-refresh cycles). This frequency was chosen because it produces the largest amplitude oscillatory MEG signal (38). The lower half of the visual field was chosen for placement of the target, because filling-in has been shown to be more robust (9) and because MEG signals have been shown to be stronger for stimuli presented in the lower visual field (39).…”

Towards an independent brain–computer interface using steady state visual evoked potentials

“…Subjects participated in several runs comparing combinations of 6, 10, 12, 15, 20, and 30 Hz with both overlapping and nonoverlapping stimuli. These frequencies were chosen to match reports of successful experiments in the SSVEP literature (e.g., Regan, 1989;Cheng et al, 2002 2 ;Beverina et al, 2003;Gao et al, 2003;Pastor et al, 2003) within the limited set of frequencies available a monitor with a 60 Hz refresh rate. Although there were substantial differences between subjects, SSVEP differences were most apparent with checkerboxes at 6 and 15 Hz and lineboxes at 10 and 12 Hz.…”

Comparison of the influence of stimuli color on Steady-State Visual Evoked Potentials

“…It is worth to comment that for both SSVEP response and classification studies, only O1, O2 and O3 electrodes were selected after the application of a Common Average Reference (CAR) spatial filter, which is based on studies that suggest that the highest values of energy for SSVEP detection are located on the occipital area of the cortex (Di Russo et al, 2007;Krolak-Salmon et al, 2003;Pastor et al, 2003;Sammer et al, 2005;Zhang et al, 2006). Thus, the twelve aforementioned electrodes were used at the initial stage only for application of the CAR spatial filter.…”

“…These frequencies were chosen due to: 1) our previous studies (Tello et al, 2014a;2014b;2014c) have shown that these generate strongest SSVEP responses; 2) safety recommendations specified in Fisher et al (2005); 3) studies conducted by Pastor et al (2003) about the relationship between visual stimuli and SSVEP-evoked amplitudes recommend these frequencies; 4) studies conducted by Herrmann (2001) showing peaks of SSVEPs at ∼15 Hz.…”