Reviews & Analysis

The evolution of complex nervous systems is not well understood. In this Opinion article, Arendt and colleagues discuss comparative gene-expression data that suggest that the bilaterian brain emerged from the integration of distinct integrative centres present on opposite sides of a nerve net.

Rodents spend a large proportion of their waking time engaged in self-grooming behaviour. In this Review, Kalueff and colleagues describe the characteristics and underlying neural circuitry of rodent self-grooming, and discuss its use as a measure of repetitive behaviour in models of psychiatric disease.

Cell surface molecule diversification has been proposed to confer specific surface identities on neuronal cell types, enabling the precise pattern of connectivity that is observed between CNS neurons. In this Review, de Wit and Ghosh explore the role of various protein superfamilies in the specification of such connectivity.

Recent years have seen several important advances in the tools available to interrogate the function of specific genes. Here, Heidenreich and Zhang describe the advantages of the precise and efficient CRISPR–Cas9 (clustered regularly interspaced short palindromic repeat–CRISPR-associated protein) system for gene editing and outline how this approach may benefit research into nervous system function and disease.

Tau is a microtubule-stabilizing protein that aggregates in several neurodegenerative diseases. In this Review, Wang and Mandelkow describe the structure, expression and post-translational modifications of tau, and the functions of this protein in health and in disease.

Endocannabinoid signalling affects the behavioural domains of acquired fear, anxiety and stress-coping by modulating synaptic functions in specific brain circuits. Lutz and colleagues discuss the cellular mechanisms involved in these effects and the potential for endocannabinoid-based therapies to treat anxiety and stress-related disorders.

The precise timing of impulse transmission along axons is crucial for synaptic plasticity and brain oscillations, and is partly determined by myelin thickness. In this Opinion article, R. Douglas Fields discusses how electrical activity influences myelin thickness and thus conduction velocity and circuit properties.

Sensory systems encode and interpret patterns of contrast in sensory signals to provide an accurate representation of an animal's environment. Maler and colleagues here outline our current understanding of the principles of contrast coding in the electrosensory system and make comparisons with contrast coding in the visual system.

Cortico–basal ganglia circuits are involved in goal-directed and habitual actions. Jahanshahiet al. review evidence for the involvement of the cortico–basal ganglia network in goal-directed and habitual inhibition, and propose that some of the symptoms of basal ganglia disorders represent an imbalance between goal-directed and habitual action and inhibition.

The cortex can generate packets of neuronal activity with stereotypical sequential structure spontaneously or in response to sensory stimuli. In this Opinion article, Luczak and colleagues examine the evidence for such packets and discuss how packets may act as fundamental units of cortical communication.

Various brain regions have been implicated in emotion regulation, although this process remains poorly understood. In this Opinion article, Etkin and colleagues bring together neuroimaging findings and ideas from value-based decision-making and reinforcement learning to propose a conceptual framework for emotion regulation.

Type 2 diabetes mellitus is associated with an increased risk of cognitive dysfunction and Alzheimer disease. In this Review, Biessels and Reagan discuss findings from human studies and animal models which suggest that hippocampal insulin resistance is one of the mechanisms underlying the links between these disorders.

Ageing leads to the gradual loss of brain function and is a key risk factor for most late-onset neurological disease. In this Review, Chow and Herrup explore how the loss of DNA integrity drives brain ageing and contributes to the pathogenesis of many seemingly unrelated conditions.

Classical theories, such as cable theory, can only successfully model signal propagation in neurons on a macroscopic scale. Holcman and Yuste argue that, as the functional importance of neuronal compartments such as dendritic spines becomes apparent, it is important to develop models that can account for the effects of their size and geometry on electrical current flow.

The brain is particularly sensitive to changes in cell number, which can acutely affect neural function. Here, Knoblich and colleagues describe the proliferation control mechanisms that exist inDrosophila melanogasterand mammals, and their regulation by developmental age and by metabolic and nutritional status.

Attention processes allow the selection of salient information over competing inputs. In this Review, Amso and Scerif propose a framework for visual attention development that incorporates its interactions with visual and memory systems and may guide the design of training programmes to alleviate attention disorders.

The causes and neurological mechanisms of tinnitus remain incompletely understood. In this Opinion, Elgoyhenet al. critically assess recent neuroimaging studies of people with tinnitus that implicate structural and functional changes among auditory and non-auditory areas and networks, and suggest ways to improve future research into the disorder.

Impairment of social cognition is an important feature of schizophrenia. Green and colleagues review the social processes that are affected in people with this disorder and consider empathy — a complex social cognitive function that involves several of these processes — in such individuals.

Cannabinoid receptors and their endogenous ligands, the endocannabinoids, are widely expressed in the brain, particularly in regions that are implicated in mediating reward. In this Review, Parsons and Hurd explore the role of endocannabinoid signalling in natural and drug-induced reward, as well as in addiction.

Fragile X syndrome (FXS) results from the loss of the RNA-binding protein fragile X mental retardation protein (FMRP). Here, Klann and colleagues discuss the ways in which FMRP loss disrupts mRNA translation in the brain and the outcomes of genetic and pharmacological attempts to reset translational homeostasis in FXS model mice.