Research articles

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.

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.

There are many mechanisms for LTD, but it remains unknown which one underlies experience-dependent plasticity during development. Wright and colleagues now report that LTD in response to developmental deprivation depends on the GluR1 subunit in barrel cortex layers 2/3 and 4.

In addition to the changes in synaptic efficacy, modifications in the intrinsic excitability of neurons are seen after learning. Using in vitro operant conditioning of feeding in Aplysia, Mozzachiodi et al. demonstrate that a long-term increase in the neuronal excitability can contribute to the storage of long-term memory.

Synaptic plasticity is believed to underlie the formation of long-term memories, but the mechanisms are not well understood. Elkobi and colleagues now report that induction of PSD-95, a synaptic protein, parallels taste learning, and attenuation of PSD-95 expression in taste cortex blocks learning of novel tastes, but not recollection of familiar ones.

It was previously known that a lack of FMRP can lead to a broad increase in protein synthesis. In this manuscript, the authors demonstrate a direct association between enhanced protein synthesis and the cognitive deficits observed in animal models lacking FMRP.

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.

This study demonstrates that several microRNA species co-regulate the levels of the ataxin1, a gene implicated in the development of spinocerebellar ataxia type 1 (SCA1). With ataxin1 dosage contributing to disease severity, this regulation pathway may influence SCA1 progression.

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.