Research articles

fMRI studies suggest that nucleus accumbens (NAc) activation increases in response to stimuli of different hedonic valence, whereas physiological evidence suggests that NAc neurons show increases in activity for rewarding stimuli and pauses for aversive stimuli. Using cyclic voltammetry, the authors find that patterns of dopamine release and metabolic activity differentiate between rewarding and aversive stimuli.

Dopamine is known to contribute to the amygdala-mediated aversive response, where increased dopamine release can augment amygdala function. Combining fMRI and PET imaging techniques, Kienast et al. present findings that suggest a functional link between anxiety temperament, dopamine storage capacity and emotional processing in the amygdala.

The authors report that fMRI responses in human foveal retinotopic cortex contain information about objects presented in the periphery. This information is position invariant and correlated with perceptual discrimination accuracy.

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.

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.