Attention stabilizes the shared gain of V4 populations

Abstract

Responses of sensory neurons represent stimulus information, but are also influenced by internal state. For example, when monkeys direct their attention to a visual stimulus, the response gain of specific subsets of neurons in visual cortex changes. Here, we develop a functional model of population activity to investigate the structure of this effect. We fit the model to the spiking activity of bilateral neural populations in area V4, recorded while the animal performed a stimulus discrimination task under spatial attention. The model reveals four separate time-varying shared modulatory signals, the dominant two of which each target task-relevant neurons in one hemisphere. In attention-directed conditions, the associated shared modulatory signal decreases in variance. This finding provides an interpretable and parsimonious explanation for previous observations that attention reduces variability and noise correlations of sensory neurons. Finally, the recovered modulatory signals reflect previous reward, and are predictive of subsequent choice behavior.

DOI: http://dx.doi.org/10.7554/eLife.08998.001

eLife digest

Our brains receive an enormous amount of information from our senses. However, we can’t deal with it all at once; the brain must selectively focus on a portion of this information. This process of selective focus is generally called “attention”. In the visual system, this is believed to operate as a kind of amplifier that selectively boosts the signals of a particular subset of nerve cells (also known as “neurons”).

Rabinowitz et al. built a model to study the activity of large populations of neurons in an area of the visual cortex known as V4. This model made it possible to detect hidden signals that control the attentional boosting of these neurons. Rabinowitz et al. show that when a monkey carries out a visual task, the neurons in V4 are under the influence of a small number of shared amplification signals that fluctuate in strength. These amplification signals selectively affect V4 neurons that process different parts of the visual scene. Furthermore, when the monkey directs their attention to a part of the visual scene, the associated amplifier reduces its fluctuations. This has the side effect of both boosting and stabilizing the responses of the affected V4 neurons, as well as increasing their independence.

Rabinowitz et al.’s findings suggest that when we focus our attention on incoming information, we make the responses of particular neurons larger and reduce unwanted variability to improve the quality of the represented information. The next challenge is to understand what causes these fluctuations in the amplification signals.

DOI: http://dx.doi.org/10.7554/eLife.08998.002