Volume 16 Issue 3, March 2013

Microglia have been regarded as the tissue macrophages of the brain. A study now finds that microglia are quite distinct from blood-borne macrophages and derive from an erythromyeloid precursor cell of the embryonic hematopoiesis.

Two studies show that local inhibitory connectivity and hippocampal excitatory input support the spatial firing patterns of entorhinal grid cells, providing support for continuous attractor model of grid cell firing.

A study recording directly from the human brain shows that connectivity between the prefrontal cortex, parietal cortex and the medial temporal lobe across different frequency bands underlies successful memory retrieval.

In this Perspective, the author examines how reading and writing the neural code may be linked. He reviews evidence defining the nature of neural coding of sensory input and asks how these constraints, particularly precise timing, might be critical for approaches that seek to ‘write the neural code’ through the artificial control of microcircuits to activate downstream structures.

The authors use Ca²⁺ imaging in freely behaving mice to look at the long-term dynamics of CA1 hippocampal place codes. They find that, in a familiar environment, there is substantial change in the population of place-coding cells over time, but the ensembles of these cells are sufficiently stable to preserve an accurate spatial representation across weeks.

In the human brain, the lateral occipital area, which is thought to support object recognition, contains two separate visual field maps, LO1 and LO2. Using transcranial magnetic stimulation, the authors identify the specialized and independent processing of orientation and shape in these two maps.

Despite substantial work highlighting the amygdala's role in fear, the authors provide a surprising finding that carbon dioxide inhalation evokes fear and panic in three patients with bilateral amygdala damage. These results indicate that the amygdala is not required for fear triggered internally rather than by external threats.

This study describes the transcriptional programming of yolk sac–derived microglia specification in the brain, in which c-kit–positive erythromyeloid cells are further modified into three developmental subpools of microglia progenitors and their microglia differentiation is mediated by the transcription factors Pu.1 and IRF8.

In this study, the authors show that an epigenetic program, operating in the hypothalamus, can regulate the timing of female puberty. They find that increased promoter methylation of two Polycomb group family members reduces their expression at the onset of puberty, allowing expression of Kiss1.

This study describes the synaptogenic function of an ErbB2-interacting protein called Erbin, particularly its function in the formation of excitatory synapses on interneurons and its regulation of AMPA-type glutamate receptors through its interaction with the auxiliary AMPA receptor protein TARP γ-2.

The authors show that insulin induces long-term depression of excitatory synapses onto ventral tegmental area (VTA) neurons in rodents, which requires endocannabinoid-mediated presynaptic inhibition of glutamate release. Insulin infusion into the VTA reduces food anticipatory behavior and conditioned place preference for food, suggesting a role for this plasticity in behavior.

Previous evidence has suggested that hippocampal place fields in rodents arise from the summation of input from entorhinal grid cells. Here the authors show that perturbing excitatory backprojections from the hippocampus to the entorhinal cortex causes a gradual firing rate–dependent loss of grid pattern and an emergence of head-directional tuning in grid cells of the medial entorhinal cortex.

Using paired recordings from rat entorhinal stellate cells and computational modeling, this study shows that stellate cells in the medial entorhinal cortex (MEC) are almost exclusively connected to each other via inhibitory interneurons in an all-or-none style and that stable grid firing can arise from this recurrent inhibitory circuitry within the MEC.

The authors performed patch-clamp recordings in the entorhinal cortex of mice navigating in a virtual-reality environment. They found that the membrane potential pattern of stellate cells during firing field crossings consists of a slow depolarization driving spike output, which is reproduced by a continuous attractor network model of grid cell firing; phase precession of spiking, however, is best explained by an oscillatory interference model.

The authors show that fear conditioning induces potentiation of excitatory synapses onto somatostatin-positive inhibitory neurons in the lateral division of the central amygdala. Preventing this synaptic potentiation impairs the formation of fear memories, and activation of these neurons is necessary and sufficient for expression of fear memories.

A stimulus predicting reinforcement can trigger emotional and cognitive responses. Here the authors report that neurons in the amygdala integrate spatial and motivational information, potentially for directing attention toward emotionally relevant stimuli. This suggests that the amygdala may be important for coordination of cognitive and emotional responses.

Using simultaneous electrocorticographical recordings in multiple lobes in human subjects performing memory retrieval tasks, this study finds that oscillatory coupling across a network of brain regions predicts successful memory recall. The study also shows that this increased network connectivity converges at the medial temporal lobe, with different neural signatures for spatial versus temporal components of episodic memory retrieval.

Age-related cognitive decline is paralleled by two other prominent brain changes: structural atrophy prominent in medial prefrontal cortex (mPFC) and disrupted non-rapid eye movement (NREM) slow-wave sleep (SWS). This study establishes an interaction between these factors, demonstrating that the extent of mPFC atrophy predicts the degree of impaired NREM SWS quality, thereby compromising hippocampal-dependent memory consolidation in the aging human brain.

In this Resource study, the authors used high-resolution mass spectrometry to elucidate the precise proteomic complement of the inner ear hair bundle. Many of the proteins that are enriched in the hair bundles are encoded by known deafness-associated genes.