Title: Mapping the microcircuitry of attention: attentional modulation varies across cell classes in visual area V4.
Authors: Jude F. Mitchell, Kristy A. Sundberg, John H. Reynolds
Abstract: Cortical neurons differ from one another in important ways, including their neurochemical properties, patterns of connectivity, laminar distribution, gene expression patterns and developmental origin. Previous studies of attention have not sought to distinguish among different classes of neurons. We therefore know almost nothing about the complex circuitry that transforms attentional feedback signals into improved visual processing. Studies in the slice and in anesthetized animals find that parvalbumin expressing GABA-ergic interneurons with the morphologies of basket and chandelier cells have short duration action potentials, whereas most excitatory cell classes have longer duration action potentials, a difference that is due to expression of different classes of sodium and potassium channels. We thus examined differences in attentional modulation across visual area V4 neurons classified on the basis of action potential width. The distribution of action potential widths in our sample of neurons was clearly bimodal. We find substantial differences in the basic response properties of these two classes of neurons, including their baseline firing rates, the strength of their stimulus-evoked responses, and variability of their responses. We also find differences in how the two neuronal classes are modulated by attention, including a substantial attention-dependent reduction in response variability among narrow spiking neurons, and a differences in the degree to which attention alters phase coherence of the two classes, with respect to ongoing network activity as indexed by simultaneously recorded local field potentials. This is the first study of attention to distinguish among different neuron types, and our findings lead to the surprising conclusion that attention has a more pronounced influence on local inhibitory interneurons than on pyramidal neurons.
