Volume 18 Issue 1, January 2015

Loss of the receptor tyrosine kinase ErbB4 in somatostatin (SOM) inhibitory neurons of the thalamic reticular nucleus (TRN) enhances top-down cortical feedback, improving feature detection at the cost of reduced ability to switch attention. The study furthers our understanding of the circuit mechanisms underlying TRN function.

The retina encodes visual information and sends it to the brain. We now learn that this neural code varies strongly with light adaptation. Does this mean a change in the message or a change in the way that the message is coded?

A study finds that formation of a cognitive map for a virtual reality environment demands associating specific movement trajectories with views to the constellation of peripheral landmarks.

Single-unit recording in primate cortical area MT shows surprising sensitivity to depth defined by dynamical perspective cues. Depth might then be computed through recurrent circuits involving signals downstream of MT.

The authors used human embryonic stem cells or induced pluripotent stem cells to derive sensory neurons that have biochemical and electrophysiological properties similar to touch receptors, including the ability to transduce mechanical stimuli into electrical activity. Using CRISPR/Cas9 gene targeting technology, they also show that the mechanosensitivity of these cells relies entirely on the expression of PIEZO2.

In this study, the authors show that they can induce the direct conversion of fibroblasts into nociceptor neurons via the expression of only five key transcription factors. They further confirm that these induced neurons are bona fide nociceptors by demonstrating that their expression profiles resemble that of their endogenous counterparts and show that they are responsive to common nociceptor agonists.

In this study, the authors show that expression of Brn3a with Ngn1 or 2 can induce the direct reprogramming of mouse and human fibroblasts into peripheral sensory neurons. They further demonstrate that these neurons exhibit the expression profiles and physiological properties of mature sensory neurons and are responsive to nociceptor agonists.

Here the authors find that PlexinA1, a well-known Semaphorin receptor, is also a receptor for Slits. Utilizing phenotypic analysis of mouse models, they define an in vivo contribution of Plexin-Slit signaling during commissural axon guidance and demonstrate the role of the Slit C-terminal fragment in this process.

Drosophila optic lobe neurons are generated from the outer and inner proliferation centers (IPC). The authors show a new mode of neurogenesis in which progenitors in one IPC domain migrate to a second domain where they mature into neural stem cells/neuroblasts. They also identify several genes that regulate this process.

Sensory stimuli fluctuate on many timescales but short-term plasticity causes synapses to act as temporal filters, limiting the range of frequencies they can transmit. Here, the authors show how the interaction of multiple synaptic and circuit mechanisms can reduce synaptic depression to promote faithful coding of both fast and slow stimuli.

Light increments and decrements are encoded in the retina by ON and OFF ganglion cells. The polarity of these cells' responses is thought to be fixed, but Tikidji-Hamburyan and colleagues now demonstrate in mouse and pig retina that they can change depending on ambient illuminance. For instance, an OFF cell can gain or lose an ON response at different light levels. Such changes in response polarity propagate to higher visual centers in vivo.

Combining patch-clamp recordings and subsequent STORM imaging of individual cells, the authors show that the axon terminals of perisomatically- and dendritically-projecting GABAergic interneurons show differences in CB₁ receptor number, active zone complexity, and receptor:effector ratio. Chronic exposure to THC evoked a dose-dependent and long-lasting downregulation of CB₁ at these synapses.

The inhibitory neurotransmitter GABA can lead to neuronal depolarization during early brain development caused by a shift in intracellular chloride concentration. Here Deidda et al. show that a brief alteration in depolarizing GABA during early development can modulate critical-period plasticity in the visual cortex later in development, and this effect is mediated by perinatal BDNF signaling.

Earlier work suggests that spatial phase preferences are randomly distributed throughout visual cortex. In this study, the authors present evidence towards a columnar organization for spatial phase that resembles organization for orientation preference, which suggests that this phase organization may contribute to the emergence of orientation maps.

The authors show that mice lacking the gene Erbb4 in somatostatin-expressing (SOM) neurons of the thalamic reticular nucleus (TRN) show selective behavioral deficits in tasks involving switching attention between cues of different sensory modalities. Slice recordings also showed enhanced cortical drive in Erbb4-deficient TRN SOM neurons.

By recording neural activity in the lateral amygdala in awake and behaving rats, Ghosh and Chattarji show that neural encoding of fear generalization involves reduction of specific response to fear-associated cues at the single-neuron level. The study also shows that increasing neuronal excitability in the lateral amygdala can promote fear generalization and that the auditory cortex is not involved when fear-inducing conditioning stimulus is based on sound.

M. Aghajan and colleagues recorded hippocampal activity in rats foraging in a two-dimensional virtual reality (VR) environment. Spatial selectivity was absent but phase precession was intact, occurring within 2-s-long hippocampal motifs. Selectivity to space and distance traveled were greatly enhanced when the rats repeatedly followed systematic paths. The results demonstrate that distal visual cues alone are insufficient to generate a robust hippocampal rate code for space but are sufficient to generate a temporal code.

Extraretinal signals such as efference copy are generally thought to be critical for discounting visual image motion caused by eye movements. However, theoretical work suggests that eye rotations could be estimated directly from optic flow. Here the authors show that MT neurons use such ‘dynamic perspective’ cues to disambiguate depth.

In this study, the authors show that monkeys can learn to use non-biomimetic proprioceptive feedback, delivered via electrical microstimulation of somatosensory cortex, to guide motor movements. The monkeys also integrated this artificial feedback with vision to optimize motor performance. The results suggest new learning-based approaches both to providing sensory feedback for brain–machine interfaces and to studying the neural mechanisms of adaptive sensory integration.

Based on single cell RNA-sequencing of 622 adult mouse sensory neurons, Usoskin et al. performed unbiased classification to identify the cellular and molecular complexity underlying somatic sensation. Eleven different subtypes were identified, including some previously unknown populations such as a new class of neuron which may be sensitive to inflammatory itch.

Brain transcriptomics is limited by existing annotations of expressed gene products. Here the authors identify differentially expressed regions of the genome across development and aging in the human brain. These transcripts were developmentally conserved across the human and mouse and enriched for genetic variants associated with neurodevelopmental disorders.