The ability to target and manipulate specific neuronal populations is crucial for understanding brain function. In this issue, Fishell and colleagues describe a novel virus that restricts gene expression to telencephalic GABAergic interneurons across a breadth of vertebrate species, allowing for their morphological visualization, activity monitoring and functional manipulation. Image: Lava Tubes in Mojave National Park.Credit: Jordane Dimidschstein.p 1743

Compared to other areas of medicine, psychiatric research faces unique biological, technological, clinical, regulatory and ethical challenges. Efforts to develop new treatments have languished for decades and the underlying causes of psychiatric disorders remain elusive. This issue focuses on psychiatric disorders and the recent advances in basic and clinical sciences advancing mental health research. The cover is a reference to the Herrenhausen Gardens in Hanover, Germany, where leaders in psychiatric research met at a symposium in May 2016 to discuss unmet needs in the field. Artwork by Lewis Long. (p 1381)

The visceral motor system produces specific outputs depending on the nature of the stimulus, such as nipple erection due to tactile stimulation or piloerection, known as goosebumps in humans, due to a frightening encounter (see cat). In this issue, Ernfors and colleagues identify the developmental mechanism producing distinct cell types that control these autonomic responses. Image credits: UrchenkoJulia, iStock/Getty Images Plus; Life on white, Alamy Stock Photo; Steve Bly, Alamy Stock Photo. (p 1331)

This focus on the neuroscience toolbox provides a select overview of modern techniques neuroscientists use to interrogate the brain at microscopic and macroscopic scales. The cover is an anachronistic depiction of Galileo, both a scientist and an engineer, and the close relationship between tools and discovery. Artwork by Lewis Long. (pp 1117–1187)

Fitzpatrick and colleagues find that synapses with similar functional properties are clustered together on the dendrites of pyramidal cells in the visual cortex, and that the degree of clustering is correlated with response selectivity. The illustration depicts a neuron that receives functionally-clustered synaptic inputs to its dendritic processes. Artwork by Marija Stojkovic.9841003

Yoshihara and colleagues identify the neural circuitry underlying the effects of the sex pheromone prostaglandin F2α on zebrafish reproductive behavior.p 897

Gage and colleagues show that dentate granule cells undergo experience-dependent homeostatic dendritic pruning—illustrated here by the arboreal shearing of the castigating tailor from Heinrich Hoffman's 19th-century German children's book Struwwelpeter. Artwork by Veronika Mertens.p 788

Animals engage in risky behaviors depending on potential gains and losses relative to current needs. For example, during starvation, they are more likely to forage for food where predators are prevalent and conspecifics can compete. Padilla et al. report a neural mechanism regulating these behaviors and describe a hypothalamic AgRP circuit controlling fear and aggression during nutritional deprivation.643734

Singh and colleagues find that rare variants in the histone methyltransferase SETD1A are associated with schizophrenia and other developmental disorders. The cover is of Oregon's Painted Hills and alludes to Waddington's epigenetic landscape: canalization routes distinct starting points towards a robust developmental phenotype or vagaries allow a similar starting point, such as the same mutation in a gene, to eventually diverge into multiple outcomes. Image by Marilyn Dunstan Photography/Alamy Stock Photo.525571

Theory and experiment have long traveled in lockstep in the physical sciences. This balance has been firmly tilted towards experiment in biology, including neuroscience. More complete biological understanding, and better experimental design, must rest on a foundation of neural theory. Without this, it might truly be turtles all the way down. Artwork by Lewis Long.347–413

Mammalian cortex contains intermingled cells of various types. Tasic and colleagues classified cells based on their single cell transcriptomic signatures and revealed 49 cell types. The cover depicts each cell type labeled with a different color intermingled in the background and organized according to their relatedness into a hierarchical tree.179335

DNA methylation regulates gene expression and orchestrates tissue differentiation and development as well as guides functional activity in adulthood. Jaffe et al. and Hannon et al. show that early developmental methylation QTLs are enriched in genomic regions associated with schizophrenia risk. The cover depicts mQTLs across the genome associated with developmental time periods of the human brain. Cover design is a mixed-media collage by Helen Spiers.14048