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.

Memories are thought to be attractor states of neuronal representations, with the hippocampus a likely substrate for context-dependent episodic memories. However, such states have not been directly observed. For example, the hippocampal place cell representation of location was previously found to respond continuously to changes in environmental shape alone. We report that exposure to novel squ...

Place cells in the hippocampus fire at specific positions in space, and distal cues in the environment play critical roles in determining the spatial firing patterns of place cells. Many studies have shown that place fields are influenced by distal cues in foraging animals. However, it is largely unknown whether distal-cue-dependent changes in place fields appear in different ways in a memory t...