Reviews & Analysis

New studies provide compelling evidence that the number and length of myelin sheaths generated by oligodendrocytes in the CNS are controlled by local calcium levels, linking axonal activity to individual myelin sheath formation.

Super-resolution optical imaging of presynaptic terminals shows that a protein essential to all known forms of neurotransmitter release is clustered in small assemblies that likely correspond to release sites for synaptic vesicle fusion.

Both nucleus accumbens and orexin play clear roles in motivated behavior, but the functions of orexin projections to accumbens are poorly understood. Blomeley et al. show that this pathway, via specific orexin excitation of dopamine D2 receptor–expressing neurons, can inhibit reward seeking and exploratory drive when danger is perceived.

The medial entorhinal cortex contains spatially selective grid cells, whose lattice-like firing patterns are proposed to support path-integration-based navigation. However, direct behavioral evidence has been lacking. Gil et al. disrupt grid cells in a targeted manner, establishing a clear link between grid cell codes and navigation.

The glial scar plays critical but divergent roles during regeneration of the mammalian CNS. Here the authors propose that in-depth analysis of the functionally heterogeneous populations of reactive glia within the scar is needed to fully understand the glial scar’s dual nature.

To decide how much we would like to eat a food item, our brain automatically decomposes it into constituent nutrients. The quantities of the different nutrients are represented in distinct parts of the lateral orbitofrontal cortex and then integrated by the medial orbitofrontal cortex to provide a global value judgment.

A leaky blood–brain barrier may contribute to neuropsychiatric disease. Chronic stress is shown to alter blood–brain barrier permeability, allowing an inflammatory response to penetrate the brain. The deficit is mostly around the nucleus accumbens, an area central to motivation. The affected animals exhibit features of depression.

Sommeijer et al. describe a previously unrecognized role of the thalamus: development of inhibition in the thalamus regulates ocular dominance plasticity, a form of critical-period plasticity regulation previously ascribed solely to the cortex.

The authors propose a new framework for the thalamus in cognition. They review findings from rodents and primates, emphasizing thalamic control of functional cortical connectivity, its putative mechanisms and role in flexible construction of task-relevant cortical networks.

Mouse models have generally failed to recapitulate the dopaminergic neurodegeneration seen in Parkinson's disease. Expressing mutant α-synuclein in a background of elevated dopamine generates mice with nigrostriatal degeneration.

The discovery of a circuit from the midcingulate cortex to the posterior insula that is essential for cortical sensitization sheds light on the plasticity mechanisms responsible for the transition from acute to chronic pain.

Physiological and optogenetic dissection of discrete locus coeruleus neuronal populations reveals a functional disassociation, with heterogeneous engagement of locus coeruleus neurons in either fear learning or extinction models.

Synaptic integration is critical for determining how information in the brain is encoded, stored and retrieved. The authors review roles for synaptic integrative mechanisms in the selection, generation and plasticity of spatially modulated firing, and in related temporal codes for representation of space.

In this Perspective, the authors propose that functional insights into generalist cortical computation may reside at the level of population patterns rather than functionally defined cell types. They then review results showing that medial entorhinal cortex (MEC) neurons exhibit substantial heterogeneity, suggesting MEC is a generalist circuit that computes diverse episodic states.

Cognitive maps are internal representations of large-scale navigable spaces. While they have been long studied in rodents, recent work in humans reveals new insights into how cognitive maps are encoded, anchored to environmental landmarks and used to plan routes. Similar neural mechanisms might be used to form ‘maps’ of nonphysical spaces.

Considerable progress has been made in understanding how the brain encodes our sense of direction. This Perspective considers the link between self-motion detection and navigation circuits and discusses future challenges for establishing the neural mechanisms responsible for sensing direction in both real-world and virtual-reality environments.

Distinct processing of objects and space has been an organizing principle for studying higher-level vision and medial temporal lobe memory. Here Connor and Knierim discuss instead how spatial information, on both local and global scales, is deeply integrated into the ventral-temporal object-processing pathway in vision and memory.

Central amygdala directs behavioral responses to emotionally salient stimuli. While most studies have focused on aversive responses, some central amygdala neurons promote feeding and are positively reinforcing.

Upon injury of the developing mouse cerebellum, endogenous repair mechanisms can heal the brain and prevent behavioral motor deficits. At the right time, with the right cues, the brain can repair itself.

Inputs to the central complex, the navigation center of Drosophila, are strongly modulated by the visual stimulus history. These history effects carry forward to bias turning behavior when flies choose between two visual stimuli.