Articles in 2008

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.

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.

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.

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.

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.

This study presents a trial-by-trial analysis of responses of Purkinje cells of the cerebellum in awake-behaving monkeys as they carry out a simple motor learning task. The results show that the presence of a complex spike on one learning trial is linked to a depression of simple-spike responses on a subsequent trial when behavioral learning takes place.

Employing molecular genetic analysis of a G protein–coupled receptor and its cognate ligands, Ringstad and Horvitz describe a neuropeptide pathway that modulates egg-laying behavior in C. elegans. This signaling pathway is shown to act in a collaborative fashion with cholinergic signaling to inhibit this behavior.

Visual sensitivity is degraded while the eyes are moving. This study now finds that sensitivity for some kinds of visual stimuli is actually improved during smooth pursuit eye movements. These sensitivity increases are likely to originate from the parvocellular retino-thalamic system.

Speech production relies on both somatosensory input from the vocal tract and auditory input. Nasir and Ostry now show that in deaf individuals, somatosensory input alone can support speech motor learning.

Recording from Kenyon cells in moths, the authors investigated the neural representations of odors that become associated with rewards through learning. They find that the spikes representing the odor do not coincide with reinforcement, suggesting that Hebbian spike timing dependent plasticity alone cannot underlie this learning.

Observers can combine multiple sensory cues to achieve greater perceptual sensitivity, but little is known about the underlying neuronal mechanisms. Gu and colleagues found neurons in the dorsal medial superior temporal area of the macaque that had responses that were consistent with the signals expected to result from cue combination.

The precuneus and the dorsal premotor cortex track changes in the positions of surrounding objects when observers move around in a virtual environment, finds this fMRI study. Importantly, activation in the dorsal premotor cortex was modulated by subjects making a motor response to indicate object positions, while the precuneus tracked positions regardless of response type.

How important is ongoing neurogenesis to the function of the adult brain? Using genetic labeling and ablation methods in mice, Imayoshi and colleagues show that ongoing neurogenesis is required for maintenance of the olfactory bulb granule neuron population. In the hippocampus, blocking neurogenesis resulted in impaired contextual and spatial memory.

Following a retinal lesion, it is known that extensive topographical remapping occurs in visual cortex. To examine the dynamics of this plasticity, Keck et al. combined chronic intrinsic and two-photon imaging to follow both the functional and structural modifications of the affected cortical region. They observed close to a complete turnover of spines on the functionally relevant cells, suggesting that a massive rewiring had occurred, producing new circuits.

The developing brain generates neurons first and glia later. This study shows that the two COUP-TF transcription factors are essential for the transition from neurogenesis to gliogenesis. COUP-TFI/II in this context appear to function as transcriptional repressors.

With aging comes a decline in remyelination efficiency, but it is currently unknown why this occurs. In this study, the authors reveal an age-dependent epigenetic mechanism that modulates the levels of oligodendrocyte differentiation inhibitors and dictates the extent of remyelination.

Dendritic protrusions have a major role in the production of glutamatergic synapses. Much less is known regarding the development of GABAergic connections. This study examined contact formation between GABAergic axons and their targets, revealing that new putative GABAergic terminals were produced through the appearance of new boutons at pre-exisiting axon/dendrite crossing points, without the participation of dendritic or axonal protrusions.

Primary visual cortex (V1) activation in humans is attenuated during perceptual suppression, but recordings of single neurons in monkey V1 show little suppression. The authors resolve this apparent conflict, finding that perceptual suppression in monkeys is associated with strong suppression of population level activation, but only weak suppression of single neuron activity.