Discussion of jsiegle's comment: Inspired by findings that PV+ interneurons increase their firing rates during attention, and that attention enhances the propagation of signals in the cortex, the authors examine how directly controlling PV cells changes functional connectivity. They activate ChR2-expressing PV cells in auditory cortex of ketamine–xylazine-anesthetized mice using 1 s pulses of blue light. Presenting a brief, pure tone stimulus evokes spikes that are measured with a 4-shank silicon probe—and subsequently used to quantify "coupling" between recording sites by fitting an Ising model. The model fit is meant to capture millisecond-timescale connectivity patterns that can't be seen with a purely correlative analysis. They find that activating PV cells reduces overall firing rates while simultaneously enhancing intra- and intercolumnal coupling, but only in the feedforward direction. The authors conclude that PV cells may play a role in dynamically regulating the flow of cortical activity in response to attentional allocation.