Volume 19 Issue 10, October 2016

Neurons require lifelong maintenance of their transcriptional program, which includes stable expression of cell-type-specific identity genes. A study now shows that PRC2-mediated chromatin repression in adulthood is critical for the maintenance of neuronal identity gene expression and neuronal survival.

Sound information travels from auditory cortex to lateral amygdala, but a newly identified pathway runs in the opposite direction. It undergoes plasticity and is required for memory recall during auditory fear conditioning.

While the relationship between motivation and sleep is intuitive, its behavioral and neural features are poorly understood. A new study tackles both issues, showing that dopaminergic neurons in the ventral tegmental area mediate this relationship.

A neural code for sequences needs to allow the recruitment of plasticity mechanisms that link successive items. New results suggest that this is achieved by coupling gamma band activity to specific phases of theta oscillations.

The dorsal anterior cingulate cortex is one of the most beguiling regions of the brain. Understanding its essential function has become a holy grail for many cognitive neuroscientists. With this scrutiny has come contention. In this issue, two teams of neuroscientists with different views argue for their favored interpretation of neural activity in this region. Here, we provide some background and context for this debate.

A number of higher cognitive processes are linked to dorsal anterior cingulate cortex (dACC), yet its overall functions remain elusive. The authors discuss convergent findings suggesting it is part of a mechanism for tracking and evaluating reward environments in order to implement learning, search and goal-driven persistence.

The authors propose that dorsal anterior cingulate cortex (dACC) performs a cost/benefit analysis to specify how best to allocate cognitive control. They describe why this theory accounts well for dACC’s role in decision-making, motivation and cognitive control, including its observed role in foraging choice settings.

The study of the mechanisms controlling RNA metabolism in neurons represents a new frontier in the understanding of gene–environment interactions and how they regulate brain function. In this Perspective, the authors describe the recent surge in newly identified epitranscriptomic processes and highlight their potential importance in coordinating the molecular underpinnings of cognition and memory.

Deficits in developmental synaptic pruning are frequently observed in autism. Here the authors demonstrate molecular pathways shared by pruning and long-term depression (LTD), a synaptic memory mechanism in adult brains that is dysregulated in autism. Thus, autism-related pruning deficits may result from the inability to weaken or disconnect inefficient synapses.

Coupling distances between synaptic vesicles and Ca²⁺ channels determine the efficacy of neurotransmission. Böhme et al. find that presynaptic scaffold complexes spatiotemporally control Unc13 isoforms to establish two independent release pathways at subsynaptic active zones: Unc13B defines nascent, loosely coupled synapses whereas Unc13A facilitates release at mature synapses by tight coupling between Ca²⁺ channels and synaptic vesicles.

Polycomb repressive complex 2 (PRC2) is a key mammalian epigenetic regulator that supports neuron specification during development. In this paper, the authors find that PRC2 plays a role in the survival of adult neurons. The loss of PRC2 activity in adult striatum led to the de-repression of multiple genes with bivalent histone methylation marks and to a fatal neurodegeneration phenotype.

The sympathetic system maintains a physiological balance, adjusts bodily functions during daily living activities, and can activate stress responses. The authors identify a variety of unique sympathetic neuronal types and show that the system is highly organized with dedicated neurons organized into discrete outflow channels for specific bodily functions.

The authors show that hypothalamic neurons that synthesize tyrosine hydroxylase regulate food intake and body weight. By a combination of dopamine and GABA release, these neurons modulate the activity of both pro-opiomelanocortin neurons and paraventricular nucleus neurons that also contribute to energy homeostasis.

The authors uncovered a pathway from the lateral amygdala to the auditory cortex (ACx) of mice that is essential for auditory fear memory retrieval. Simultaneous imaging of pre- and postsynaptic structures in ACx in vivo revealed an increased rate of synapse formation in this pathway after auditory fear conditioning.

Motivated behaviors are critically dependent upon arousal but little is known about the neuronal mechanisms that coordinate motivational processes with sleep–wake regulation. The authors demonstrate that VTA dopaminergic neurons, which are central regulators of motivational processes, bidirectionally regulate sleep–wake states and sleep-related nesting behavior.

The authors find that the portion of rat somatosensory cortex representing the trident whiskers—a set of whiskers specialized for ground contact during exploration—encodes information about speed and acceleration of the animal. Microstimulation of this area alters running speed, consistent with the idea that trident whiskers and their neural representation could serve as a tactile speedometer.

A core aspect of human episodic memory is the ability to recall events in the order that they were experienced. The authors found that successful memory for order is related to the precise timing of high frequency brain activity with respect to slower underlying rhythms.