The cover image shows a numerical simulation of 10,000 years of river migration. How permafrost influences the erosion and migration of rivers has largely been unclear. In this week’s issue, Emily Geyman and colleagues start to resolve this issue, focusing on the Koyukuk River in Alaska. The researchers used a novel computational method that allowed them to resolve erosion of the river’s banks at scales much smaller than the pixel size in satellite imagery, changes that are not visible to the human eye. They found that permafrost reduced riverbank erosion by 47% compared with areas where no permafrost was present. They also found that, if the permafrost thaws, it could lead to a 30–100% increase in the rate of river migration. With some 43% of Arctic villages situated next to rivers, the team suggests climate-induced thaw of permafrost could have significant implications.

Neurons in the brain are connected by synapses to form sophisticated circuits that drive complex behaviours such as social interaction and navigation. But to understand how these circuits work requires a map of all the synaptic connections — a ‘connectome’. In a series of papers in this week’s issue, the FlyWire Consortium unveils and analyses the complete connectome of the brain of an adult female fruit fly (Drosophila melanogaster), identifying around 140,000 neurons and more than 50 million synaptic connections. In the first paper, the consortium, led by Mala Murthy and Sebastian Seung, presents the full wiring diagram of the fly’s brain along with a network analysis of the connectome. Gregory Jefferis, Davi Bock and colleagues annotate neurons in the connectome, and compare them across individuals, while Seung, Murthy and colleagues annotate the optic lobes, and Murthy and co-workers offer a statistical analysis of the connectome’s structure. Sung Soo Kim, Mathias Wernet and co-workers focus on the fly’s visual system to provide insight into the circuitry behind navigation. Seung uses connectivity data to uncover a new neural circuit and predict its role in visual function, and Salil Bidaye and colleagues describe a neural circuit for halting behaviour. Philip Shiu and co-workers take the entire connectome and transform it into a computational model to create a sort of ‘digital twin’ of the fly brain. Finally, Jonathan Pillow and colleagues investigate subcircuits of the connectome and define a path for finding an ‘effectome’ from the data.