Volume 16 Issue 6, June 2013

Intrahippocampal transplantation of inhibitory interneuron progenitors derived from the medial ganglionic eminence markedly ameliorates the seizure activity and neurobehavioral deficits typically observed in the pilocarpine mouse model of mesial temporal lobe epilepsy, even if the cells are engrafted after the onset of spontaneous seizures.

A study shows that circadian glucocorticoid oscillations have dual roles in dendritic spine plasticity, controlling spine formation and elimination through distinct mechanisms important for motor learning.

Two studies in this issue report the discovery of different types of uncertainty signals in little-studied, but critical, regions of the forebrain: decision confidence in the pulvinar and reward risk in the anterodorsal septum.

A study reports that fixation and optomotor responses in Drosophila rely on parallel neural processing of position and motion information, but interact at the behavioral level.

Prior anatomical studies have suggested that intratelencephalic (IT) and pyramidal tract (PT) cortical neurons project to different populations of striatal spiny projection neurons (SPNs). Here, the authors find using optogenetic stimulation that both IT and PT neurons project to both direct and indirect pathway SPNs.

In this study, the authors use time-lapse in vivo two-photon imaging to elucidate the dynamics of NG2⁺ gial cells in the cortex. They find that proliferation and migration of these cells is intimately linked to the loss of neighboring cells to cell death or differentiation.

In this study, the authors show that Dscam, a gene that has been implicated in Down syndrome, is targeted by the translation suppressor and Fragile X–linked protein FMRP. Loss of FMRP or overexpression of Dscam in Drosophila led to synaptic targeting errors and an impairment in perception of mechanical stimuli.

In this study, the authors identify the ER-localized protein Meigo as a modulator of dendritic and axonal targeting of olfactory neurons. They find that Meigo is essential for maintaining protein levels and N-glycosylation of Ephrin in the ER, thereby regulating its function in axonal and dendritic refinement.

In this study, the authors show that MGE-derived interneuron progenitors, when engrafted into the adult hippocampus, can migrate long distances and functionally integrate into the host tissue. In addition, if these cells are engrafted into the brain after the initiation of epilepsy, seizure frequency and behavioral deficits are reduced.

Long-term exposure to glucocorticoids following chronic stress is detrimental to cognitive processes including learning and memory. Even so, short term glucocorticoid surges can facilitate cognition. Here the authors show that the circadian oscillation in circulating glucocorticoids is important for motor skill learning–induced dendritic spine remodeling. They also show that circadian glucocorticoid-mediated synaptic modification acts through non-transcriptional mechanism involving cytoskeleton remodeling and correlates with long-term memory retention.

Early-life stress, acting through corticotrophin-releasing hormone (CRH) and its receptor CRHR1, can have long-lasting effects on animals' behavior. Nectin-3 is a cell adhesion molecule whose heterodimeric interaction with presynaptic nectin-1 organizes the postsynaptic afadin–actin–N-cadherin complex to shape synaptic structure and function. Here, the authors show that structural synaptic adaptation and cognitive dysfunction in adulthood following early-life stress are dependent on CRH signaling acting through Nectin-3.

Temporal and spatial integration of synaptic inputs onto dendrites can display linear, sublinear and supralinear motifs in vitro. A study now examines this issue in vivo in mouse binocular visual cortex. It shows that dendritic integration of binocular information is sublinear, leading to a divisive form of gain control that linearizes the output of binocular neurons and enhances orientation selectivity.

In primary visual cortex (V1), adaptation controls the responsiveness of individual neurons and shifts their visual selectivity. Here the authors examine adaptation at the population level. They conclude that adaptation in V1 acts as a mechanism of homeostasis, enforcing a tendency towards equality and independence in neural activity across the population.

In response to the movement of its visual world, Drosophila is capable of optomotor response in head and body turning, as well as a visual fixation response. This study shows that blocking the visual pathway activity responsible for optokinetic response in flies does not affect the visual fixation response, suggesting two distinct pathways for processing each set of information. By doing so, the authors also devised a neural and behavioral hierarchy in fly visual system where fixation behavior and the neurons mediating fixation response are upstream of optokinetic response as performed by lobula plate neurons.

Prevailing models have suggested that grid cell firing in the entorhinal cortex for spatial navigation relies on theta rhythmic inputs from head direction cells. Here, the authors show how head direction cells can skip theta cycles in a regular and organized manner in which two head direction cells will alternate theta skipping in opposing cycles. This so-called theta skipping is dependent on the input from the septum, and these results propose a possible mechanism of spatial computation.

Here the authors report evidence for the neural correlates of confidence in the primate pulvinar, a visual thalamic nucleus. Data from electrophysiological recordings, functional silencing and theoretical modeling indicate that pulvinar activity encodes a subject's certainty of visual categorization and contributes to perceptual confidence, which potentially underlies visual awareness.

Making informed decisions requires taking into account how reliably choices produce expected outcomes. This study shows that primate anterodorsal septal neurons encode an uncertainty signal sensitive to reward size but do not carry information about the uncertainty of punishments.

The authors use functional magnetic resonance imaging to measure how the semantic representation changes when searching for different object categories in natural movies. They find tuning shifts that expand the representation of the attended category and of semantically related, but unattended, categories, and compress the representation of categories semantically dissimilar to the target.