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Spontaneous population activity bursts promote the development of brain circuits. This study shows that single GABAergic hub neurons exert a strong influence on spontaneous and sensory-evoked population bursts in the mouse barrel cortex.

A common anatomical feature of the sensory cortex in many species is that neurons with similar features cluster into vertically orientated domains spanning all layers of the cortex. Moreover, neurons in one domain modulate neurons in neighbouring domains through horizontal connections. A combination of techniques has now been used to show that such horizontal projections suppress layers of cortex devoted to processing inputs, but facilitate layers devoted to outputs.

Neurons that respond emergently to illusory contours drive pattern completion in V1. Pattern completion in lower cortical areas may therefore mediate perceptual inference by selectively reinforcing activity patterns that match prior expectations.

The activity of somatostatin-expressing inhibitory neurons (SOMs) in the superficial layers of the mouse visual cortex increases with stimulation of the receptive-field surround, thereby contributing to the surround suppression of pyramidal cells.

Using two-photon (2P) optogenetics and computational modeling, the authors find that neither space-based nor feature-based rules are sufficient to describe cell–cell interactions within the primary visual cortex (V1). Instead, models must include interactions between these cardinal axes.

ChRmine is a bacteriorhodopsin-like cation channelrhodopsin (BCCR). Here, the authors present cryo-EM structures of ChRmine in apo- and retinal-bound forms to provide insight into channel activity in a BCCR and facilitate engineering of ChRmine-based optogenetic tools.

The authors develop a new computational system for high-throughput mapping of synaptic connectivity using two-photon holographic optogenetics and intracellular recordings.

Layer six in the mouse primary visual cortex is a major mediator of cortical gain modulation and may be a node through which convergent inputs from several brain areas can regulate the earliest steps of cortical visual processing.

The cortex is sensitive to weak stimuli, but also responds to stronger inputs without saturating. In this study, Scanziani and colleagues find some of the circuits that enable neuronal populations to respond to a wide range of input strengths.

The authors establish a critical role for somatostatin interneurons in visually induced gamma oscillations in the primary visual cortex of mice. Optogenetic manipulations in awake animals, combined with an innovative computational model with multiple interneuron subtypes, provide a mechanism for the synchronization of neural firing across the retinotopic map.

Optogenetics, the optical stimulation of neurons, suffers from many technical challenges that limit the number of neurons that can be excited as well as their relative positions. Here, Pégard et al. develop a method to simultaneously stimulate an arbitrary number of neurons in 3D space with single neuron resolution.

Optogenetic suppression of layer 4 in the sensory cortex reveals a surprising role for its activity in the cortical microcircuit: layer 4 suppresses the main cortical output layer—layer 5—through a direct translaminar inhibitory circuit. This translaminar inhibition sharpens spatial representations in the somatosensory cortex.

The authors present a new approach to create and edit custom spatiotemporal neural activity patterns in awake, behaving animals with extremely high spatial and temporal precision. They present novel opsins optimized for multiphoton optogenetics.

Multiphoton holographic optogenetics is opening the era of ‘tailored’ optogenetics. The authors review the underlying technology and discuss how it can be used to bridge the gap between experimental and theoretical neuroscience.

This review discusses recent advances in optogenetic pharmacology, discussing its potential to manipulate endogenous neuronal signaling proteins. These approaches include caged agonists and antagonists and reversibly photoswitchable ligands.