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Analysis of samples from the asteroid Ryugu provide evidence of late fluid flow in a carbonaceous asteroid, indicating that such bodies may have retained two to three times more water than previously thought.

Neural mechanisms underlying memory acquisition and encoding are not fully understood. Here authors show that during sleep, besides the replay of past memory, coactivity of a new set of cells arises (engram-to-be) to encode future memory by the aid of offline synaptic scaling. This dual process preserves past memories while shaping new ones for the future.

The authors propose a learning rule for a neuron model with dendrite. In their model, somatodendritic interaction implements self-supervised learning applicable to a wide range of sequence learning tasks, including spike pattern detection, chunking temporal input and blind source separation.

Behavioral responses vary considerably across individuals. Kurikawa et al. show experimentally and computationally how the observed spectrum of individual variances in decision-making emerges from neural dynamics of the medial frontal cortex.

The contribution of individual circuit elements to experience-dependent synaptic plasticity in the brain remains unknown. An intracellular analysis of the changes that occur when an eye is deprived of vision in early life now reveals a counterintuitive initial shift towards the occluded eye followed by a late preference for the open eye. These results, combined with intracellular pharmacology, suggest that inhibitory neurons have a major role in shaping experience-dependent plasticity in the developing visual cortex.

The brain stores memories through a set of neurons known as engram cells. Here, the authors show that engram cells in the mouse hippocampus are organized into sub-ensembles representing distinct pieces of information, which are then orchestrated to constitute an entire memory.

A comparison of copper and zinc isotopic measurements between the Ryugu samples and various carbonaceous chondrites excludes any genetic link between the two except for the CI (Ivuna-type) chondrites. Ryugu-like material might have accounted for ~5% of Earth’s mass.

The asteroid Ryugu experienced aqueous alteration under changing temperature and redox conditions, according to an isotopic analysis of secondary calcite and dolomite grains in samples from Ryugu obtained by the Hayabusa2 spacecraft.

A close-up look at the action of space weathering on carbonaceous asteroids, provided by Ryugu’s returned samples, highlights its role on the dehydration of the first micrometre-thick layer of the surface, possibly hiding a water-rich interior. The depth of the 2.7 µm hydration band may be an indication of the level of space weathering withstood by a C-type asteroid.

Using a closed-loop virtual reality system for fish, the authors show that zebrafish are capable of assigning rules to the scenery they see, and of generating a state prediction error by comparing reality with a prediction derived from an internal model.

Systematically monitoring the activities of various cortical pyramidal neurons and interneurons during different stages of locomotion, the authors characterize differential firing activities of motor cortex microcircuitry in behaving, head-restraint rats that were trained to push, pull or hold a lever for reward.

The Hayabusa2 spacecraft returned 5.4 g of material from the asteroid Ryugu. A first analysis of the samples found an estimated density of 1,282 ± 231 kg m⁻³, considerably lower than even the most porous meteorites. Together with preliminary spectral analysis, these results indicate that Ryugu is similar to CI chondrites, but darker, more porous and more brittle.