Volume 11 Issue 11, November 2008

Oldham et al. present a systematic analysis of gene coexpression relationships in specific human brain regions with the goal of identifying groups of genes with common coexpression patterns. The study used the inherent structure of the brain's transcriptome to find data-driven organizational patterns rather than rely on external classification systems.

A recent paper reported the in vitro generation of new prion strains, supporting the idea that 'strain-ness' is encoded in the protein structure itself. This lays the groundwork for a reinvigorated study of prion structure–pathology relationships.

A paper in this issue reports that the core mechanisms that strengthen memories have more in common with the mechanisms that support reconsolidation than those that participate in their initial storage.

Previous work has focused on neuronal encoding of two-dimensional shapes. Using a new search algorithm and three-dimensional object primitives, a study in this issue identifies potential subunits of complex object recognition.

Combined population activity is usually used to control neural prosthetics. A recent study in Nature finds that a single primary motor cortex neuron can control the artificial stimulation of paralyzed wrist muscles to move a computer cursor.

In a process termed lateral inhibition, nascent neurons via expression of Notch ligands are thought to suppress neuronal development of adjacent cells. It has recently been shown, however, that expression of the Notch ligands, as well as the proneural transcription factors that induce them, and the Notch effector Hes1 oscillate with a period of a few hours. This dynamic expression pattern is incompatible with the notion of lateral inhibition and demands a new understanding of how all-over oscillatory expression patterns are converted to localized and persistent signaling.

The authors report that the action potential voltage threshold is actually higher in the axon than elsewhere in the neuron, but as the current threshold at the axon is lower than elsewhere, the action potential threshold is indeed lowest in the axon.

Under some in vitro conditions, neurons of the deep cerebellar nuclei show a phenomenon called rebound potentiation, where, following a strong hyperpolarization, their membrane potential briefly rebounds to a more depolarized level causing a transient increase in firing rate. The authors, however, found that under more physiological conditions in vitro or in vivo, deep cerebellar nuclei neurons rarely showed rebound potentiation. This finding necessitates a re-evaluation of some cerebellar models, where rebound potentiation was postulated to be involved in plasticity and/or information processing.

Subcortical auditory neurons show adaptation-dependent coding of sound intensity. Recordings in awake marmoset reveal two populations of intensity-sensitive neurons at the cortical level: one that has a dynamic range that adapts to the statistics of the environment and another that does not, preserving sensitivity to the lowest intensities.

Auditory cortex neurons fire with high temporal precision to the fine timing of acoustic stimuli. Here, the authors show that stimulation in this area in rat brains, even when differing by as little as 3 ms, can be used to guide decisions.

Memories are dynamic and the reactivation of memories via re-exposure to training stimuli can cause the destabilization of a memory trace. This paper shows that the subsequent reconsolidation of this memory can modify the strength of contextual fear memory during learning.

Shmuelof and Zohary report that actions seen from an allocentric point of view evoke more activation in the ipsilateral anterior parietal cortex than those seen from an egocentric point of view, even in the absence of active imitation, supporting the idea that there is a mirror-image representation of action in this brain region.

The authors analyze gene coexpression relationships in microarray data generated from specific human regions. They identify modules of coexpressed genes that correspond to neurons, oligodendrocytes, astrocytes and microglia, demonstrating that cell type-specific information can be obtained from whole brain tissue without isolating homogenous populations of cells.

Nearly all sensory neurons express the transcription factor Isl-1. Isl-1 is essential for the development of motoneurons, but its role in sensory neurons has been unknown. Using conditional knockout limited to neural crest derivatives, this study shows that Isl-1 is necessary for the survival of nociceptive and mechanoreceptive neurons during later embryogenesis.

Recent work has suggested a role for astrocyte dysfunction in the etiology of amyotrophic lateral sclerosis (ALS) caused by mutations in superoxide dismutase (SOD1). Lepore et al. show here that transplantation of astrocyte-restricted progenitors in fact improves survival of rats expressing a human ALS-associated SOD1 allele. The rescue effect required the astrocytic glutamate transporter GLT1.

Microdeletions of the chromosome locus 22q11.2 are linked to a variety of mental and neurological disorders in human, including schizophrenia. Using a mouse strain carrying a synthenic microdeletion, Mukai et al. show dendritic spine defects associated with the hemizygous loss of the 22q11.2 locus, which includes the gene responsible for neuronal protein palmitoylation.

The contribution of fatty acids to Alzheimer's disease pathogenesis is unclear. The authors identify an increase in arachadonic acid and its metabolites in a mouse model for Alzheimer's disease and show that amyloid-beta (Aβ) affects phosphorylation of an isoform of phospholipase A₂ (GIVA-PLA₂). Inhibiting activation of GIVA-PLA₂ protected against Aβ-induced toxicity and prevented some Aβ-induced deficits in learning and memory.

Structural changes in the dendrites are mediated in part by a cell adhesion molecule, β-catenin, and are associated with memory formation and maintenance. A new study by Maguschak and Ressler shows that β-catenin has a selective role in fear memory consolidation.

Using in vivo microdialysis in zebra finches, the authors show that forebrain steroid levels (estradiol and testosterone) are differentially regulated in a region-specific manner in response to various behavioral contexts. Moreover, the time course of this modulation is similar to that of traditional neuromodulators.

Neural systems adapt to changes in stimulus statistics. The authors find that neocortical pyramidal neurons adapt with a time scale that depends on the time scale of changes in stimulus statistics, and that for individual neurons the firing is a fractional derivative of slowly varying stimulus parameters.

Nearby retinal ganglion cells show correlated activity in the absence of visual stimuli and these correlations are propagated across the population. A combination of recordings and computational modeling suggest that shared synaptic input is the origin of this synchrony.

The role of inferotemporal cortex in coding two-dimensional patterns has been extensively studied, but the more difficult problem of three-dimensional shape representation has been relatively unexplored. Yamane and colleagues use new techniques for adaptive stimulus presentation and response modeling to extensively characterize neural coding for three-dimensional objects.