Articles in 2008

The transcription factor FoxP1 is important for the establishment of motor neuron diversification and connectivity. New studies indicate that it acts as an accessory factor for the transcriptional output of the Hox transcription factor network.

The adult mouse brain continuously supplies new neurons to the olfactory bulb and hippocampus. A new study in this issue shows that ongoing neurogenesis is essential for maintenance of the olfactory bulb and for spatial memory.

Spike-timing dependent plasticity is a favored synaptic mechanism for learning. However, a surprising new study by Ito and colleagues in the insect mushroom body suggests that it cannot account for a paradigmatic form of learning.

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.

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.

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 perspective article proposes a general law (Bouma law), which states that a visual object is crowded (and therefore cannot be perceived) when spacing between multiple objects is less than a critical spacing value. Crucially, this value is independent of the object.

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.