Volume 17 Issue 3, March 2014

A study shows the transience of early visual representations (while the stimulus is still on) and the persistence of higher representations (outlasting the stimulus) as various categorical distinctions emerge at staggered latencies. Rather than slavishly following the stimulus, representations interact through recurrent signals to infer what's there.

A study now suggests that tau-induced reactive oxygen species relax chromatin, which leads to expression of PIWIL1, cell cycle reentry and neurodegeneration.

Feeding effects of CB₁ receptors are commonly associated with exogenous cannabinoids, but a study now identifies a circuit by which endocannabinoid activation of CB₁ receptors in the main olfactory bulb regulates normal food intake.

A study finds that, during movement preparation, when motor cortex is active, but elicits no muscle output, firing of individual neurons in dorsal premotor and primary motor cortex cancels out at the level of population activity.

In this Perspective, the authors review the literature and suggest that the cognitive pathology that often accompanies preterm birth and/or very low birth weight may be a direct result of perinatal hypoxia that, in turn, leads to perturbations in the maturation and development of interneurons, oligodendrocytes and astrocytes.

Working memory is thought to be limited in capacity, holding a fixed, small number of items, but it has recently been proposed that working memory might be conceptualized as a limited resource that is distributed flexibly between all items to be maintained in memory. In this review, the authors consider emerging evidence for this proposal.

The authors show that there is global loss of heterochromatin in tau transgenic Drosophila and mice, and post-mortem brain from Alzheimer's disease patients. Oxidative stress and DNA damage mechanistically link tau and heterochromatin loss. Finally, they show that reversing tau-induced heterochromatin loss reduces neurodegeneration in tau transgenic Drosophila.

The authors show that leucine-rich repeat kinase 2 (Lrrk2) binds protein kinase A (PKA) regulatory subunit IIβ to decrease PKA activity in striatal projection neurons (SPNs). Lrrk2 regulation of PKA prevents its synaptic translocation, altering synaptogenesis and transmission in developing SPNs. A Parkinson's disease–associated mutant of Lrrk2 prevented its interaction with PKARIIβ.

In this study, the authors show that altering the photoperiod of mice results in reversible transcriptional and DNA methylation changes in the suprachiasmatic nucleus. Application of a methyltransferase inhibitor blocks the light-entrained changes in the circadian period, suggesting that these methylation changes directly mediate circadian plasticity.

In vitro evidence suggests that the tuft dendrites of pyramidal neurons can evoke local NMDA spikes. The authors find that these local NMDA spikes occur spontaneously and following sensory input, and influence the number of output action potentials.

This study shows that early neonatal sensory deprivation of one modality can impact cortical plasticity of other sensory cortices because of the reduction in dendritic release of oxytocin from paraventricular hypothalamic neurons. The study also shows that exogenous oxytocin can attenuate the effects of neonatal sensory deprivation on cortical plasticity, thus mimicking the beneficial effects of enriched sensory exposure.

Microglia are involved in synaptic pruning during development. Here the authors show that mice deficient in the fractalkine receptor Cx3cr1, which show a transient reduction in microglia, have reduced synaptic multiplicity in the hippocampus, decreased functional connectivity between the prefrontal cortex and hippocampus and altered social and repetitive behaviors.

This study shows that activation of cannabinoid type-1 (CB1) receptors in the olfactory bulb increases odor detection and food intake in hungry mice. The authors show that this function is mediated by CB1-dependent attenuation of excitatory corticofugal synaptic transmission onto inhibitory granule cells and disinhibition of mitral cells in the main olfactory bulb.

To adaptively navigate their environments organisms need to predict and cancel out the sensory consequences of their actions. Here the authors show that granule cells within the cerebellum-like structure of weakly electric fish have delayed responses that closely match the timing of self-generated sensory inputs. This enables corollary discharges to be transformed into negative images that are well-tuned to the animal's own behavior.

The authors trained mice to perform rapid action sequences while recording from neurons in the direct and indirect basal ganglia pathways. In addition to neurons whose activity reflected the start or stop of a sequence, they identified neurons that displayed sustained activity or inhibition throughout an entire action sequence.

The authors use monkey electrophysiology data to test a “bump attractor” computational model. Their findings reinforce persistent activity as a basis for spatial working memory, provide evidence for a continuous prefrontal representation of memorized space, and offer experimental support for bump attractor dynamics mediating cognitive tasks in the cortex.

Brain areas directly involved in driving movement are active well before movement begins. Muscle activity is some readout of this neural activity, yet remains largely unchanged during preparation. Here the authors find that during movement preparation, changes in motor cortical activity cancel out at the level of population activity within dorsal premotor and primary motor cortex.

The pedunculopontine nucleus (PPN) is a target for deep brain stimulation for the control of gait and postural disability, but its role in gait control is not understood. Here, using extracellular single-unit recordings in awake patients, the authors show that neurons in the PPN respond to limb movement and imagined gait by dynamically changing network activity and decreasing alpha phase locking.

Using representational similarity analysis to link human MEG with human fMRI and monkey electrophysiological data, the authors provide an integrated temporal and spatial account of object categorization. Early, low-level processing corresponded to activity in primary visual cortex, while later object processing related to inferior temporal activity in a category-specific manner.

Decision-making research has often focused on decisions between two options. The authors adapted a decision-making model to account for a third, unavailable option, and they found that decision-making was more difficult with a poorer, and not better, third alternative. Ventromedial prefrontal cortex activity predicted individual variation in decision-making with multiple options.

In this Technical Report, the authors describe a new methodology for rapid and flexible knockdown of specific proteins in vitro and in vivo—without the need for genetic modification of the target—using a small peptide construct that targets the protein of interest and marks it for chaperone-mediated autophagy.