Articles in 2008

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.

Following brief stimulation, macroscopic NMDA receptor currents decay with biphasic kinetics believed to reflect glutamate dissociation and receptor desensitization. The authors show that the fast and slow decay components arise from the deactivation of receptor populations that gate with short and long openings.

Adenosine receptor A_2AR is known to antagonize dopaminergic signaling in the striatum and its malfunctions have been implicated in various striatum-related diseases. Flajolet et al. show that A_2AR and fibroblast growth factor receptor interact to synergistically activate ERK1/2 pathway and that such interaction modulates the morphological changes of cultured neurons and synaptic plasticity of cortico-striatal synapses.

Hippocampal GABAergic synapses are excitatory during the early postnatal period and can undergo spike timing-dependent modifications of synaptic strength. Xu and colleagues demonstrate that this plasticity can be modulated bidirectionally by frequency and that it depends on the action of GABA_B receptors.

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.

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.

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.

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.

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.

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.

About 4% of the cells in the adult rodent brain are PDGFRA⁺ NG2⁺ glia, derived from the oligodendrocyte lineage. Rivers and colleagues constructed a transgenic mouse to fate map the PDGFRA⁺ glia. In the adult corpus callosum, these cells generated substantial numbers of late-myelinating oligodendrocytes. In the cortex, little late myelination was observed; instead, PDGFRA⁺ precursors seemed to continuously generate small numbers of projection neurons mainly in piriform cortex.

Previous work suggests that post-learning rapid eye movement (REM) sleep is crucial for memory consolidation, but this study shows that suppressing REM sleep via serotonin/norepinephrine reuptake inhibitors instead enhances memory consolidation of a motor skill task.

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.

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.

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 private philanthropy to research has been growing. Although these large infusions of money can galvanize research, private and public funds now increasingly seem to support similar projects. Caution is warranted to prevent funding for specific topics from skewing research to the detriment of other fields.

The visual and vestibular systems encode different, but complementary, aspects of self motion. A study in this issue sheds light on how the brain combines cues from these disparate sources, which are encoded by single neurons in the monkey extrastriate visual cortex, to support the perception of heading direction.