Abstract
The aim of this study is to uncover the network dynamics of the human visual cortex by driving it with a broadband random visual flicker. We here applied a broadband flicker (1-720 Hz) while measuring the MEG and then estimated the temporal response function (TRF) between the visual input and the MEG response. This TRF revealed an early response in the 40-60 Hz gamma range as well as in the 8-12 Hz alpha band. While the gamma band response is novel, the latter has been termed the alpha band perceptual echo. The gamma echo preceded the alpha perceptual echo. The dominant frequency of the gamma echo was subject-specific thereby reflecting the individual dynamical properties of the early visual cortex. To understand the neuronal mechanisms generating the gamma echo, we implemented a pyramidal-interneuron gamma (PING) model that produces gamma oscillations in the presence of constant input currents. Applying a broadband input current mimicking the visual stimulation allowed us to estimate TRF between the input current and the population response (akin to the local field potentials). The TRF revealed a gamma echo that was similar to the one we observed in the MEG data. Our results suggest that the visual gamma echo can be explained by the dynamics of the PING model even in the absence of sustained gamma oscillations.
Highlights
The properties of the neuronal dynamics governing the visual system are highly debated
The stage is set for further investigating how the gamma echo is modulated by tasks such as spatial attention as well as uncovering how the echo might propagate in the visual hierarchy
Broadband visual stimulation reveals alpha and gamma echoes in the visual system The temporal response function (TRF) of a system can be estimated by deconvolving its input and output
Summary
The properties of the neuronal dynamics governing the visual system are highly debated. The projector makes it possible to stimulate the visual system with broadband flickering stimuli while measuring the brain response using magnetoencephalography (MEG) This approach allows for estimating the temporal response function (TRF). The TRF can be considered a simple model capturing the filter properties of the visual cortex In previous studies, such an approach has been used to investigate the dynamical properties of the visual system at lower frequencies. Using a broadband flicker (1–80 Hz), the TRF was approximated from the cross-correlation between the EEG and the input signal [9] This approach revealed a robust response in the alpha range termed “the perceptual echo”. The aim of this study was to ask if the TRF has a band-limited response at higher frequencies, to uncover the faster dynamical properties of the visual system. The TRF function has a clear response at higher frequencies which is limited to the gamma band
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