Volume 20 Issue 2, February 2017

Representations in excitatory neurons generally narrow as they are refined. Odor representations in interneurons, however, broaden with maturation and learning, as connections between interneurons and projection neurons expand.

The biological drive to consume salt ensures that we consume adequate sodium for survival. In this issue of Nature Neuroscience, two articles provide insight into the neurons and circuits that regulate sodium appetite.

Many spatial correlates have been identified that form the neural basis for navigation. Two studies have now uncovered a new cell type: bidirectional cells, which fire when the head is pointing in one of two opposing directions.

Pregnancy results in changes to maternal physiology and brain that may extend into older age. New results show that pregnancy-induced reductions in gray matter volume remain 2 years after childbirth in humans.

Historically, the CNS has been considered immunologically privileged and separated from the peripheral immune system. In this Review, the authors highlight recent advances in our understanding of how the CNS interacts with peripheral immune cells in the context of health and disease.

Neural pathways regulate immune responses and inflammation. Recent research using technological advances in molecular genetics has provided important insights into the functional anatomy and cellular and molecular mechanisms of this regulation. These advances resulted in clinical trials exploring neuromodulation in the treatment of inflammatory and autoimmune disorders.

Activation of putative aldosterone-sensitive neurons in the hindbrain drives mice to drink sodium solutions, and this appetite is distinct from thirst and hunger. These neurons are critical for animals to fully develop a sodium appetite following sodium depletion, although there is likely redundant circuitry.

Using an environment composed of interconnected paths, the authors demonstrate that subiculum encodes a previously unrecognized form of spatial information, the axis of travel. This discovery has implications for how path positions and orientations can be related to the larger environment.

The authors report on a subpopulation of neurons in retrosplenial cortex that is more sensitive to head direction in a local, visually defined reference frame than to global head direction. These neurons may be the means by which visual landmark information can influence the overall sense of direction.

The hypothalamus is a brain region rich in functionally segregated neurons. Here Romanov and colleagues use single-cell RNA sequencing to distinguish 62 neuronal subtypes and define their neuropeptide and neurotransmitter makeup. They then show that onecut-3-containing dopamine neurons populate the periventricular area and are wired into the circadian circuitry.

The authors show that, unlike the consolidation and refinement of excitatory connections observed during sensory map formation, a dramatic broadening of patterned activation domains, connectivity, and tuning occurs in interneurons in the olfactory bulb. This developmental expansion is sensitive to activity manipulations and may reveal general principles of interneuron network development.

Vision is processed across multiple cortical areas that are organized into two subnetworks in primates. However, the generality of this organization and its development are unclear. Smith and colleagues present functional evidence for the analogous two subnetworks in mice and map their differential developmental dynamics.

The authors developed small-molecule inhibitors of STOML3 oligomerization, a membrane protein that interacts with mechanosensitive ion channels, such as Piezo2. One of these molecules was effective in silencing touch receptors and reversed touch-evoked pain associated with nerve injury or diabetic neuropathy.

The authors show that postsynaptic deletion of neuroligin-3 from parvalbumin interneurons causes a decrease in NMDA-receptor-mediated excitatory postsynaptic currents and an increase in presynaptic glutamate release probability linked to a deficit in presynaptic Group III metabotropic glutamate receptor function. This selective disruption of excitatory transmission on parvalbumin interneurons leads to abnormal hippocampal network activity and a decrease in contextual fear extinction.

Body fluid conditions are continuously monitored in the brain in order to regulate thirst and salt appetites. Through a combination of optogenetics and electrophysiology, the authors reveal distinct neural mechanisms in the subfornical organ for generating appropriate water- and salt-intake behaviors according to body fluid conditions.

Episodic memory involves encoding an event's temporal and spatial context. The authors show that temporal information is mediated by a direct projection from the dorsal CA1 field of the hippocampus to the medial prefrontal cortex, while spatial information is processed in a separate hippocampal–prefrontal cortex projection originating in intermediate CA1.

How the hippocampus and sensory cortical regions interact during memory consolidation is largely unknown. The authors identify a rapid loop of information flow from auditory cortex to the hippocampus and back, around the times of hippocampal sharp wave ripples, which coordinates memory reactivation during sleep across these brain areas.

The authors describe cortical projections mediating the modulation of social behavior. Neural projections from the medial prefrontal cortex to the dorsal periaqueductal gray play a critical role in the behavioral adaptation to social defeat in mice.

Emotional arousal is known to produce long-lasting memories for emotional experiences. Here the authors find that brain states associated with emotional arousal can persist tens of minutes later, biasing and enhancing how new, unrelated information is encoded into memory and later remembered.

Cognitive tasks require storing and manipulating information for short periods of time. Verbal working memory involves storing and manipulating speech information, but the underlying brain mechanisms remain unknown. The authors identify storage systems for sensory and motor representations and two distinct manipulation systems, demonstrating that multiple subsystems comprise verbal working memory.

The authors show that pregnancy involves substantial and consistent structural changes in the human brain, primarily located in regions subserving social cognition. These changes overlap with areas that respond to the mothers' babies and predict measures of postpartum maternal attachment. Moreover, they endure for at least 2 years after pregnancy.

The nervous and immune systems communicate and reciprocally influence their functional responses. Nature ImmunologyandNature Neurosciencepresent a joint focus entailing a series of specially commissioned review articles that discuss how the nervous system and immune cells interact during development, homeostasis and in pathogenic disease states.