Articles in 2008

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.

Our understanding of the neurobiology and treatment of psychiatric illness in children remains poor. Prominent psychiatrists have now been accused of concealing the extent of their financial ties to the drug industry. We urgently need to encourage more science in this area and we need vigorous regulation to restore some neutrality to the field.

Although the CNS has a robust innate ability to repair demyelinated axons, this capacity appears to dissipate with age. A study in this issue suggests that epigenetic processes participate in myelin repair and that the epigenetic response is less dynamic in older individuals.

Spontaneous ultra-slow oscillations in brain signals are ubiquitous, although their source and function remain unknown. A new study now reports that this activity is correlated between functionally related areas across hemispheres in humans.

The neural basis of aggression is poorly understood. A study in this issue used genetic scalpels to dissect the circuitry of the fly brain and identified a small cluster of octopaminergic neurons that can make a fly fighting mad.

Mitogen-activated Protein Kinases (MAPKs) are critical for the formation of stable long-term memories. New work shows that circadian MAPK activity cycling is important in the formation of new hippocampus-dependent memories.

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.

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.

Spontaneous cortical waves have been widely observed, although previous evidence from humans has been indirect, using functional magnetic resonance imaging. This study reports that there are slow modulations in neuronal firing rates and gamma local field potentials in human auditory cortex in the absence of sensory stimuli or task.

Structural sexual dimorphism in the developing nervous system can lead to functional differences in physiology and behavior. Postnatal, gender-based differences in cell number were presumed to be passively maintained, but here, Ahmed et al. reveal an active mechanism modulated by sex hormones that maintains different numbers of cells in sexually dimorphic brain areas.

The central serotonergic system is an important modulator of neural circuitry that regulates behavior and emotion state of an animal. Current study from Lerch-Haner et al. shows that mutant female mice with defective serotonergic neurons exhibit gross maternal neglect resulting in offspring death, and that this defect can be rescued by expression of a homologous gene from human.

Ambient light can acutely modulate sleep and can be detected by the retina independently of photoreceptors. A new study from Foster and colleagues shows that photosensitive retinal ganglion cells, with their activation of sleep-promoting centers, mediate this irradiance-dependent sleep induction.

Neurons expressing Agouti-related protein (AgRP) and neuropeptide Y (NPY) in the hypothalamus are involved in regulation of feeding and body weight, but genetic disruption of AgRP and NPY have little effect on energy homeostasis. A new study from Tong et al. shows that the energy homeostasis function is mediated through their GABAergic transmission.