Hippocampal place cells are active when the rat is at certain locations. The sequence of these active place cells is known to be rapidly replayed during sharp-wave-ripple events in the EEG. In this issue of Neuron, a study by Gupta et al. challenges previous notions that the replayed trajectories are solely a passive echo of past episodes. Rather, replay might also be an active process construc...

Place cells are a fundamental component of the rodent navigational system. One intriguing implication of place cells is that humans, by extension, have "map-like" (or GPS-like) knowledge that we use to represent space. Here, we review both behavioral and neural studies of human navigation, suggesting that how we process visual information forms a critical component of how we represent space. Th...

Attractor neural network theory has been proposed as a theory for long-term memory. Recent studies of hippocampal place cells, including a study by Leutgeb et al. in this issue of Neuron, address the potential role of attractor dynamics in the formation of hippocampal representations of spatial maps.

The identification of 'place cells' in the hippocampus has suggested a special role for this brain structure in spatial mapping, but other studies have indicated a more general role in memory. New findings on place cells point the way towards a reconciliation of the mapping and memory views.

This paper shows how to stably merge two sequences A and B of sizes m and n, m n, respectively, with O…m ‡ n† assignments, O…m log…n=m ‡ 1†† comparisons and using only a constant amount of additional space. This result matches all known lower bounds and closes an open problem posed by Dudzinski and Dydek in 1981. Our algorithm is based on the unstable algorithm of Mannila and Ukkonen. All techn...

The hippocampus has long been associated with navigation and spatial representations, but it has been difficult to link directly the neurophysiological correlates of hippocampal place cells with navigational planning and action. In recent years, large-scale population recordings of place cells have revealed that spatial sequences are stored and activated in ways that may support navigational st...

CA1 place cells discharge in prospective and retrospective modes, possibly reflecting memory retrieval and encoding, respectively. In this issue of Neuron, Bieri et al. (2014) report that slow and fast gamma oscillations associate with prospective and retrospective discharge, indicating that gamma oscillations organize information-processing modes.

Discussions of the hippocampus often focus on place cells, but many neurons are not place cells in any given environment. Here we describe the collective activity in such mixed populations, treating place and non-place cells on the same footing. We start with optical imaging experiments on CA1 in mice as they run along a virtual linear track and use maximum entropy methods to approximate the di...

We develop and evaluate humanoid balance controllers that can recover from unexpected external perturbations of varying magnitudes in arbitrary directions. Balance strategies explored include ankle and hip strategies for in-place balance, as well as single-step, double-step, and multi-step balance recovery. Simulation results are provided for a 30 DOF humanoid.