Brief Communications in 2014

Anxiety symptoms may arise from an overgeneralization of negative memories to include more neutral ones. Here the authors show that the tuning of amygdala neurons for a conditioned stimulus broadens and matches the behavioral generalization to innocuous stimuli.

Primate cortex can be organized with specialization and hierarchical principles, but presently there is little evidence for how it is organized temporally. Across six separate datasets, the authors find a hierarchical ordering of intrinsic fluctuation of spiking activity, with timescales that increase from sensory to prefrontal areas.

Synaptic remodeling in the brain is dependent on the extracellular matrix remodeling mediated by zinc-dependent matrix metalloproteinases (MMPs). Using a rodent model, this study shows that the activity of MMP2 and 9 are differentially increased in the brain region nucleus accumbens after withdrawal from self-administered cocaine, during cue-induced relapse. Along with a similar response following relapse to other drugs of abuse, the study also shows that the increased MMP activity was needed for both relapse behavior and relapse-associated synaptic plasticity that included changes to the glutamate-mediated currents and dendritic spine head diameter.

In this study, the authors show that optogenetic photostimulation of dopaminergic (DA) neurons in the ventral tegmental area during exploration can enhance subsequent sharp wave/ripple-mediated reactivation of spatial memory. These results suggest that midbrain DA neurons are key mediators of hippocampal-dependent memory persistence.

This study uses fMRI to find that the previously reported amyloid-β-associated hyperactivation is likely to represent a compensatory mechanism, rather than pathological overexcitation. The authors found that older adults with amyloid-β depositions had more activation during a memory task, and the degree of detailed memory formation varied with this activity.

This study uses data from patients with damage to specific parts of the frontal cortex to provide causal evidence for the role of the dorsolateral prefrontal cortex in enabling honest behavior. Damage to this area was associated with decisions that prioritized the decision-maker's own self-interest, at the cost of honesty.

The authors report that increased promoter methylation of the serotonin transporter gene predicts increased threat-related amygdala reactivity and decreased mRNA expression in postmortem amygdala tissue. This provides converging evidence for epigenetic regulation of behaviorally and clinically relevant human brain function.

Olfactory bulb mitral and tufted cells are thought to be particularly active at rest and to respond weakly to odors during wakefulness. By using blind, whole cell recordings in awake mice, Kollo and colleagues now reveal the existence of a previously overlooked subpopulation of mitral/tufted cells that are silent at rest but respond greatly to odors.

Neurons make homeostatic adjustments to the strength of their synapses on the basis of their activity levels. Here the authors show the microRNA miR-92a represses the translation of the AMPA receptor subunit GluA1 and that, during activity blockade, its levels are reduced to increase the incorporation of new AMPA receptors.

Sensitization leads to hyperalgesia and depends on mechanisms similar to those involved in memory formation. Here, Bonin and De Koninck find that hyperalgesia can be reversed by combining reactivation of peripheral afferents with spinal administration of a protein synthesis inhibitor, thereby identifying a spinal analogue of memory re-consolidation that enables erasing pain hypersensitivity.

Melanocortin 4 receptors (MC4Rs) in the CNS regulate metabolism. Here the authors examine extra-hypothalamic MC4Rs in the autonomic nervous system and find that they contribute to energy and glucose homeostasis.

In this study, the authors show that conditional deletion of leptin receptors from astrocytes alters their morphology and results in an increase in the number of synapses on POMC and AgRP neurons of the arcuate nucleus. In addition, they find that loss of leptin response in astrocytes modified leptin- and ghrelin-controlled food intake.

Lucid dreaming, in which the sleeper is aware of the dream state, has been associated with increased neural activity around 40 Hz (lower gamma band), but their causal relationship remains unclear. The authors show that, during REM sleep, fronto-temporal transcranial stimulation in the lower gamma band can induce lucid dreaming.

Sensory processing deficits are observed in individuals with Rett syndrome and MeCP2-deficient mice. Here, the authors show that it is the loss of MeCP2 specifically in forebrain inhibitory neurons that leads to deficits in auditory-evoked local field potentials and elicits the seizures observed in MeCP2-deficient mice.

In this study, the authors use measures of carbon-14 in neuronal DNA from human stroke patient cortical tissue samples to show that, unlike previous studies done in rodents, they do not find any evidence of increased neurogenesis after an ischemic injury. In addition, DNA damage assays suggest that there is no increase in DNA rearrangement after this insult.

In this paper, Clancy and colleagues introduce an optically driven brain machine interface (BMI) based on the processing of optical calcium signals recorded using two-photon microscopy. When applied to mouse cortex, this approach revealed that learning in a BMI-mediated operant task is accompanied by the progressive spatial refinement of activity in local networks comprising output-relevant neurons.

In this study, the authors show that the heritable behavioral and metabolic changes that are observed in rodents exposed to early life stress are mediated by changes in miRNA levels in the sperm of affected males. Injection of isolated RNA from the sperm of stressed males into donor fertilized oocytes is able to induce these phenotypic changes in the resulting offspring.

Many mouse models of Alzheimer's disease (AD) rely on overexpression of amyloid precursor (APP) transgenes, which makes it difficult to tease out which effects are truly disease-relevant and which are induced by the overexpression. In this study, the authors describe several new knock-in AD model mice that express mutant APP at near physiological levels.

The authors identify mutations in the MATR3 gene as a cause of ALS and dementia in several families. MATR3 is known to bind the ALS-associated protein TDP-43, and at least one of these mutations alters the efficiency of this binding.

The authors show that sharp-wave events recorded in mouse hippocampal slices are more likely to involve neurons that have been activated during a recent behavioral episode. The excitation/inhibition balance of the synaptic inputs received by these cells during sharp waves is biased toward excitation, suggesting a potential mechanism for their preferential recruitment into these network events.