Brief Communications in 2016

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.

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.

In this study, the authors reveal distinct developmental programs underlying innate and learned olfactory behaviors by demonstrating that chemogenetic inactivation of neurons generated in neonatal mice impairs the behavioral response to aversive odorants, whereas inactivation of adult-born neurons impairs learning of novel food-related odors.

The authors describe a glutamatergic septoentorhinal pathway that provides running-speed-correlated input to MEC layer 2/3. The speed signal is integrated by several MEC cell classes and converted into speed-dependent output. This speed circuit may be important for the spatial computations of MEC neurons.

The authors describe neurons in the macaque anterior thalamus tuned to pitch and roll orientation relative to gravity, independently of visual landmarks. Individual cells exhibit two-dimensional tuning curves peaking at a preferred vertical orientation. These results identify a thalamic pathway for gravity cues to influence three-dimensional spatial orientation.

In the CNS, the primary signal initiating myelination and its cellular origin remain unclear. Goebbels et al. find that deleting PTEN from cerebellar granule cells drives radial axon growth, oligodendrocyte progenitor cell (OPC) proliferation, oligodendrocyte differentiation and de novo myelination of parallel fibers. This suggests that myelination is downstream of a neuronal PI(3,4,5)P₃-dependent signal.

Rare genetic mutations that disrupt the functionality of important genes increase the risk of psychiatric and neurodevelopmental disorder. This study found that, in the general population not diagnosed with such disorders, these same mutations affect the average educational level. Carriers of these mutations have on average half a semester less of education than noncarriers.

In this study, the authors show that LTP lacks synapse specificity in hippocampi of aged (21–28 months) mice, possibly resulting from diminished levels of the K⁺/Cl⁻ cotransporter KCC2 and depolarizing GABA_A receptors. The KCC2 enhancer CLP257 restored synapse specificity of LTP, providing a possible new target for repairing memory loss in senescence.

Prefrontal–hippocampal communication has been implicated in memory, but the temporal dynamics of information flow are not fully understood. In this study, the authors demonstrate that information flows between hippocampus and prefrontal cortex in different directions depending on the behavioral phase of a spatial-context-guided object discrimination task.

The authors analyzed the exome sequences of 2,104 intellectual disability patients and their parents. They identified 10 novel candidate genes associated with specific clinical phenotypes.

Safaiyan et al. demonstrate that myelin fragments progressively pinch off from aged myelin sheaths and are taken up and cleared by microglia. Age-associated myelin breakdown is substantial and saturates the degradative capacities of microglia, leading to lysosomal storage and an immune activation in microglia with time.

Feeding is controlled by hedonic cues that may override the homeostatic needs to eat, causing obesity. Labouèbe et al. have identified hypoglycemia-activated neurons in the paraventricular thalamus that increase motivated sucrose-seeking behavior. As their activity is not suppressed by fructose or sweeteners, these cells may contribute to sugar overconsumption and diabetes.

Hedonic value is a dominant aspect of olfactory perception. The authors combine immediate early gene mapping and optogenetics to show that the degree of behavioral attraction to odors is represented along the antero-posterior axis of the ventral olfactory bulb. This suggests that organization of the olfactory bulb reflects hedonic value.

By combining neuroimaging with an implicit behavioral measure (mouse-tracking), the authors demonstrate that stereotypes can alter the brain's visual representation of a face's gender, race, and emotion. Perceptions of social categories were biased by a subject's stereotypical associations, and this bias correlated with neural representations of those categories.

In this study the authors have imaged the growth of adult-born dentate granule cell dendrites in vivo longitudinally over several weeks. They have found that branch addition is dependent on behavioral experience and molecular cues and that pruning acts homeostatically to promote a similar dendritic structure for all granule cells.

Theories propose hippocampal memories are consolidated to the cortex during reactivation events known as replay. However, the involvement of the medial entorhinal cortex (MEC) in consolidation remains poorly understood. Ólafsdóttir et al. demonstrate coordinated replay between the hippocampus and MEC, with hippocampus leading, suggesting hippocampal memories are broadcast to MEC.

The authors document a novel neurogenic mechanism to explain the clinical syndrome known as spinal cord injury–induced immune deficiency. Specifically, they show that new spinal–splenic sympathetic circuitry forms below the level of injury, creating an exaggerated sympathetic anti-inflammatory reflex. Inhibiting excitatory interneurons within this circuitry blocks immune suppression.

Expectations about what will appear next guide perception. Using high-resolution fMRI and multivariate pattern analysis, the authors find that such predictive coding in early visual cortex could arise from pattern completion in hippocampal subfields. They show that these two processes are related and explore their behavioral significance and relative timing.

Optogenetic inhibition of specific axonal projections is a potentially powerful technique for assessing defined neural pathways’ contributions to behavior. The authors report that while optogenetic inhibition can efficiently attenuate presynaptic release, it can under some conditions lead to undesired effects such as depolarization and increased spontaneous release.