Volume 16 Issue 2, February 2013

Work reported in this issue has derived the long-sought analytical link between neural readout weights and choice signals in the standard model of perceptual decision making. This fresh perspective opens the door to experimental assessments of percept formation from the activity of sensory neurons.

Matthew Larkum discusses the results of a large-scale patch-clamp study revealing the existence of two new cortical microcircuits. These circuits both originate in layer I and either inhibit or disinhibit layer V pyramidal cells.

A study optogenetically generating or suppressing activity in excitatory neocortical neurons in vivo finds that layer 5 pyramidal cells initiate and maintain widespread UP states, whereas layer 2/3 cells are subsidiary.

Nociceptors respond to both painful and itchy stimuli. MrgprA3-expressing neurons have now been found that are sparsely distributed in the skin and sense a wide variety of pruritogens.

A recent New Jersey Supreme Court decision has led to new jury instructions explaining that memory does not operate like a video recording. The authors discuss cognitive neuroscience research on memory and how it might contribute in the courtroom.

In their Perspective article, Lattal and Wood discuss the latest progresses on behavioral features of persistent memory formation, and how epigenetics is forcing a re-evaluation of behavioral and molecular distinctions between memory extinction and memory reconsolidation.

In this review, György Buzsáki and Edvard Moser discuss the most recent evidence suggesting that the navigation and memory functions of the hippocampus and entorhinal cortex are supported by the same neuronal algorithms. They propose that the mechanisms fueling the memory and mental travel engines in the hippocampal-entorhinal system evolved from the mechanisms supporting navigation in the physical world.

This Review article discusses in the context of learning and memory the function of sleep to earmark which daily event or information should be consolidated and which mundane information should be discarded, and how this 'memory triage' process is a selective and yet generalization process that can also bind features together in a non-congruous manner when they are recalled.

In this review, the authors highlight recent progress made in fear learning and memory, differential susceptibility to disorders of fear, and how these findings are being applied to understanding, treatment, and possible prevention of fear disorders in the clinic.

In this study, the authors show that velocity-dependent lag normalization in the retina is accomplished via a subset of adjacent directionally selective ganglion cells that are electrically coupled, allowing each activated cell to prime its neighbor.

The accessory olfactory bulb consists of anterior (aAOB) and posterior (pAOB) portions that control distinct aspects of social behavior. In this study, the authors show that, unlike their aAOB counterparts, pAOB neurons arise at the diencephalon-telencephalon border and migrate rostrally. A similar migration is seen in the Xenopus AOB.

This study shows that a non-clustered protocadherin, NFPC, is locally translated in retinal axons in response to Sema3A and demonstrates that NFPC-mediated homophilic adhesion helps guide retinal axons in the optic tract, thus revealing a new mechanism for axon guidance by linking a diffusible cue to adhesion-based navigation.

Dorsal root ganglion neurons respond to both painful and itchy stimuli, but whether itch-specific neurons exist was, up until now, unknown. Here the authors describe a group of MrgprA3-expressing neurons that innervate the superficial layers of the skin and selectively sense itch.

Treatment of pain with morphine leads to paradoxical hyperalgesia. The authors provide evidence that morphine-induced hyperalgesia is a result of downregulation of the chloride transporter KCC2 in spinal lamina I neurons. Microglial expression of P2X4 receptors and release of BDNF may underlie this change in neuronal chloride homeostasis and morphine-induced hyperalgesia.

Thalamocortical axonal inputs to the neocortex terminate in the cortical layer 4, whereas corticobulbar and corticospinal output from the cortex mostly originate from layer 5B pyramidal neurons. This study utilizes a novel in vivo gene expression system in postmitotic neurons and demonstrates the reprogramming of layer 4 input-receiver neurons in postnatal mice into layer 5B–like cortical output neurons using the expression of the transcription factor Fezf2.

The authors report that calcium channels with a mutation associated with Timothy syndrome cause activity-dependent dendrite retraction in rodent neurons and in induced pluripotent stem cell–derived neurons from individuals with Timothy syndrome. This retraction was independent of Ca permeation but was associated with activation of RhoA signaling.

Using simultaneous quadruple-to-octuple whole-cell recordings in rat sensorimotor cortex and testing over 14,000 putative synaptic connections between over 8,000 cells, Jiang and colleagues identify two new multi-layer disynaptic interneuronal circuits. Functionally, these two circuits either inhibit or disinhibit the initiation of complex spikes in the apical dendrite of layer 5 pyramidal cells.

Tuning of neurons in higher visual cortices is less diverse than in primary visual cortex (V1), but the mechanisms underlying this specialization are unknown. In this paper, Glickfeld and colleagues used two-photon imaging in awake mice to measure the visual responses of boutons from V1 projection neurons in the higher visual areas and found that bouton tunings matched the preference of their target areas. These findings suggest that inter-areal visual stimulus feature segregation occurs via the target-specific routing of visual information as it ascends the cortical hierarchy.

This study uses optogenetics in vivo in mice to provide causal evidence for the distinct roles played by different cortical layers in the regulation of intrinsic oscillations.

Here the authors derive the mathematical relationship among the key ingredients of the standard neural decision-making model: choice probabilities, read-out weights and correlated variability. This allows them to infer decoding strategies from experimentally measurable quantities and to test whether the organism is using an optimal decoding strategy for a given task, even without knowing the underlying correlations.

The authors studied how neurons in three frontal cortical areas encode the outcomes of social decisions as monkeys performed a social reward allocation task. Orbitofrontal cortex (OFC) neurons signaled received rewards, anterior cingulate (ACCs) neurons signaled forgone rewards, and the ACCg emerged as a key nexus for the computation of shared experience and social reward.

Memories provide a link between the present and the past and allow us to project our thoughts into the future. But memories are not immutable; instead, they continually evolve throughout their lifetime, embarking on a dynamic journey the moment they are born. Recent Neuroscience research has provided important new insights into how memories change in time, the mechanisms by which these changes come about and about the nature of the underlying neural representations, sometimes offering promises for the treatment of memory disorders. Nature Neurosciencepresents a focus on memory, comprising Commentaries, Reviews and Perspectives discussing some of the most exciting recent developments and emerging ideas in our understanding of the neurobiology of learning and memory.