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The hippocampus serves a critical function in memory, navigation, and cognition. Nature Neuroscience asked John Lisman to lead a group of researchers in a dialog on shared and distinct viewpoints on the hippocampus.

The medial prefrontal cortex (mPFC) is involved in changing behavioural strategies. Recording neural ensembles in rats, Powell and Redish find that the requirement for those changes is represented in mPFC before they manifest behaviourally, both in tasks that externally force a change and in tasks with self-determined change.

Geometry is crucial in spatial reorientation, but the underlying neural mechanisms of spatial reorientation are unclear. Here, the authors show that in a two-context reorientation task, distinct CA1 cells code heading retrieval and context recognition during reorientation.

The authors use three latent-state learning tasks to test how people approximate the complexities of the external world with simplified internal representations that generalize to novel examples or situations. They show that behaviour can be captured by a model combining prototype representations with goal-oriented discriminative attention.

During a single theta cycle, discrete groups of hippocampal place cells can produce a distributed series of spikes called a theta sequence. Such sequences represent the time-compressed trajectory of an animal running in its environment and usually extend ahead of the current position. Here, Wikenheiser and Redish find that the ‘look-ahead’ distance of rat theta sequences can predict the imminent choice of the animal in a value-guided decision making task.

Computationally parallel ‘change-of-mind’ tasks in mice, rats and humans are analysed and demonstrate that sensitivity to sunk costs during re-evaluation depends on the awareness of time spent and remaining.

Sometimes when rats come to a location where a choice has to be made, they pause and look around, a behaviour that has been termed 'vicarious trial and error' (VTE). Redish reviews this behaviour and its underlying neurophysiology, and argues that VTE is probably the behavioural phenotype of a deliberative process.

Spatial navigation and memory depend on neural coding of an organism’s location as well as large-scale knowledge of the environment, but how animals organize information in task-relevant spatial segments is not well understood. Here the authors show that, in rats, perirhinal neurons perform integrative operations, globally specifying where, in the task context, an animal is located.

Hippocampal place cells encode information about an animal's spatial world. A study now finds that these same neurons envisage a future journey moments before a rat sets off. See Article p.74

Differences in neuroeconomic decision-making influence nucleus accumbens dopamine dynamics and reflect choice confidence during evaluation, as well as past and future value during re-evaluation, which can causally lead to change-of-mind behaviors.

This paper reports that hippocampal theta sequences and their corresponding spatial paths stretch forward or backward as a function of an animal's behavior and that these firing sequences map the environment in segments of variable lengths or 'chunks'.

Neuroeconomic theories suggest that conflict during decision, such as exhibited by relapsing drug addicts who continue drug use despite stated wishes not to, might arise from separable processes in decision making. Here the authors test mice in a foraging task designed to separate these processes and find that mice show alterations in separable components of decision conflict following abstinence from cocaine versus morphine.

In situations that would be expected to induce regret, the authors report that rats looked backwards towards a lost option, the cells in OFC and ventral striatum represented that missed action, rats were more likely to wait out a long delay, and then they rushed through consuming rewards, suggesting that regret-like processes modify decision-making in nonhuman mammals.

The authors report that the ultrastructure and plasticity of excitatory synapses connecting dentate gyrus and CA3 of the hippocampus are severely compromised in a transchromosomic mouse model of Down syndrome. These alterations are accompanied by unstable information coding by CA3 and CA1 place cells, which may contribute to aspects of impaired cognition in the disease.

Coordinated neuronal activity may mediate memory in hippocampal CA1. Here, the authors use an array of machine-learning classifiers to reveal how higher-order population dynamics and learning-induced spine plasticity are disrupted in amnestic mice.

Head direction cells have been hypothesized to form representations of an animal's spatial orientation through internal network interactions. New data from mice show the predicted signatures of these internal dynamics.

Two major classes of inhibitory neurons in mouse anterior cingulate cortex, somatostatin and parvalbumin interneurons, form functionally homogeneous populations that are recruited at distinct moments in time and encode unique behavioral variables in a foraging task.

An optogenetic, spatial self-stimulation task in mice reveals how information carried by distinct inputs to the nucleus accumbens shell is potentially integrated to drive behavioural responses.

Recent studies have attributed surprisingly similar functional roles to the orbitofrontal cortex (OFC) and hippocampus. Evidence is presented that both the OFC and hippocampus contribute to 'cognitive mapping', and it is suggested that future work should focus on understanding the functional interactions between these structures.