Attention selectively gates afferent signal transmission to area V4

Abstract

Selective attention causes visual cortical neurons to act as if only one of multiple stimuli are within their receptive fields. This suggests that attention employs a, yet unknown, neuronal gating mechanism for transmitting only the information that is relevant for the current behavioral context. We introduce an experimental paradigm to causally investigate this putative gating and the mechanism underlying selective attention by determining the signal availability of two time-varying stimuli in local field potentials of V4 neurons. We find transmission of the low frequency (<20Hz) components only from the attended visual input signal and that the higher frequencies from both stimuli are attenuated. A minimal model implementing routing by synchrony replicates the attentional gating effect and explains the spectral transfer characteristics of the signals. It supports the proposal that selective gamma-band synchrony subserves signal routing in cortex and further substantiates our experimental finding that attention selectively gates signals already at the level of afferent synaptic input.

A model for attentional information routing through coherence predicts biased competition and multistable perception

“…We also investigated information transmission for the case that both stimuli were present and S A was attended in the same parameter regimes using the method of Grothe et al (2015): We computed the spectral coherence between the two competing, temporally modulated input stimuli and the neuronal activities in the second layer. Figure 6A shows an example of the spectral coherence for ϭ 1.…”

“…Around the mean, the firing rates of S A and S B are independently modulated by a uniformly distributed random process with an amplitude of 2 Hz, where every 10 ms a new value is drawn. This models the effect of the luminance "flicker" signal used in the study of Grothe et al (2015).…”

“…The spectral coherence is a measure that was used to quantify information transmission between luminance signals and the activity of neurons in V4 by Grothe et al (2015). For two signals x(t) and y(t) it is defined as…”

“…These results suggest that attention selectively modulates the information flow through the visual hierarchy. Grothe et al (2015) tested this hypothesis directly for the first time: by independently varying the luminance of two stimuli eliciting equally strong responses in V4 neurons, it was found that the luminance modulation of the attended stimulus was represented in the neuronal activity, but the modulation of the nonattended stimulus, however, was represented to a much lesser degree.Fries (2005) proposed a possible mechanistic explanation for these effects by introducing the concept of "Communication through Coherence" (CTC): a neuron with oscillating membrane potential can be driven to fire by relatively weak input when it is close to the threshold, while if it is in a phase of low excitability, even stronger input might fail to elicit an action potential. Thus shifting relative phases of oscillating sending and receiving populations could be utilized to gate information.…”

“…These results suggest that attention selectively modulates the information flow through the visual hierarchy. Grothe et al (2015) tested this hypothesis directly for the first time: by independently varying the luminance of two stimuli eliciting equally strong responses in V4 neurons, it was found that the luminance modulation of the attended stimulus was represented in the neuronal activity, but the modulation of the nonattended stimulus, however, was represented to a much lesser degree.…”