A minimal synaptic architecture is proposed for how the brain might perform path integration by computing the next internal representation of self-location from the current representation and from the perceived velocity of motion. In the model, a place-cell assembly called a “chart ” contains a twodimensional attractor set called an “attractor map ” that can be used to represent coordinates in any arbitrary environment, once associative binding has occurred between chart locations and sensory inputs. In hippocampus, there are different spatial relations among place fields in different environments and behavioral contexts. Thus, the same units may participate in many charts, and it is shown that the number of uncorrelated charts that can be encoded in the same recurrent network is potentially quite large. According to this theory, the firing of a given place cell is primarily a cooperative effect of the activity of its

Hippocampal ‘place ’ cells and the head-direction cells of the dorsal presubiculum and related neocortical and thalamic areas appear to be part of a preconfigured network that generates an abstract internal representation of two-dimensional space whose metric is self-motion. It appears that viewpoint-specific visual information (e.g. landmarks) becomes secondarily bound to this structure by associative learning. These associations between landmarks and the preconfigured path integrator serve to set the origin for path integration and to correct for cumulative

Previous studies have shown that hippocampal place fields are controlled by the salient sensory cues in the environ-ment, in that rotation of the cues causes an equal rotation of the place fields. We trained rats to forage for food pellets in a gray cylinder with a single salient directional cue, a white card covering 90 ” of the cylinder wall. Half of the rats were disoriented before being placed in the cylinder, in or-der to disrupt their internal sense of direction. The other half were not disoriented before being placed in the cylin-der; for these rats, there was presumably a consistent re-lationship between the cue card and their internal direction sense. We subsequently recorded hippocampal place cells and thalamic head direction cells from both groups of rats as they moved in the cylinder; between some sessions the cylinder and cue card were rotated to a new direction. All

Strong constraints on the neural mechanisms underlying the formation of place fields in the rodent hippocampus come from the systematic changes in spatial activity patterns that are consequent on systematic environmental manipulations. We describe an attractor network model of area CA3 in which local, recurrent, excitatory, and inhibitory interactions generate appropriate place cell representations from location- and directionspecific activity in the entorhinal cortex. In the model, familiarity with the environment, as reflected by activity in neuromodulatory systems, influences the efficacy and plasticity of the recurrent and feedforward inputs to CA3. In unfamiliar, novel, environments, mossy fiber inputs impose activity patterns on CA3, and the recurrent collaterals and the perforant path inputs are subject to graded Hebbian plasticity. The hippocampus is known to be involved in spatial learning and memory in rodents. Some of the most convincing evidence for this is the presence of place cells in areas CA3 and CA1 of the hippocampus (O’Keefe and Dostrovsky, 1971; O’Keefe, 1976) and of many other types of spatially selective cells in neighboring areas

A model of place-cell firing is presented that makes quantitative predictions about specific place cells' spatial receptive fields following changes to the rat's environment. A place cell's firing rate is modeled as a function of the rat's location by the thresholded sum of the firing rates of a number of putative cortical inputs. These inputs are tuned to respond whenever an environmental boundary is at a particular distance and allocentric direction from the rat. The initial behavior of a place cell in any environment is simply determined by its set of inputs and its threshold; learning is not necessary. The model is shown to produce a good fit to the firing of individual place cells, and populations of place cells across environments of differing shape. The cells' behavior can be predicted for novel environments of arbitrary size and shape, or for manipulations such as introducing a barrier. The model can be extended to make behavioral predictions regarding spatial memory. Hippocampus 2000;10:369--379. 2000 Wiley-Liss, Inc.

abstract To better understand how hippocampal place cell activity is controlled by sensory stimuli, and to further elucidate the nature of the environmental representation provided by place cells, we have made recordings in the presence of two distinct visual stimuli under standard conditions and after several manipulations of these stimuli. In line with a great deal of earlier work, we find that place cell activity is constant when repeated recordings are made in the standard conditions in which the centers of the two stimuli, a black card and a white card, are separated by 135� on the wall of a cylindrical recording chamber. Rotating the two stimuli by 45� causes equal rotations of place cell firing fields. Removing either card and rotating the other card also causes fields to rotate equally, showing that the two stimuli are individually salient. Increasing or decreasing the card separation (card reconfiguration) causes a topological distortion of the representation of the cylinder floor such that field centers move relative to each other. We also found that either kind of reconfiguration induces a position-independent decrease in the intensity of place cell firing. We argue that these results are not compatible with either of two previously stated views of the place cell representation; namely, a nonspatial theory in which each place cell is tuned to an arbitrarily selected subset of available stimuli or a rigid map theory. We propose that our results imply that the representation is map-like but not rigid; it is capable of undergoing stretches without altering the local arrangement of firing fields. key words:

To further elucidate the links among synaptic plasticity, hippocampal place cells, and spatial memory, place cells were recorded from wild-type mice and transgenic “R(AB) ” mice with reduced forebrain protein kinase A (PKA) activity after introduction into a novel environment. Place cells in both strains were similar during the first exposure and were equally stable for recording sessions separated by 1 hr. Place cell stability in wild-type mice was unchanged for sessions separated by 24 hr but was reduced in R(AB) mice over the longer interval. This stability pattern parallels both the reduced late-phase long-term The spatial mapping theory of O’Keefe and Nadel (1978) seeks to explain, as hippocampal functions, the ability of rodents to perform familiar spatial tasks, to learn new spatial tasks, and to store memories about spatial tasks. Their theory is based on the existence of place cells, hippocampal pyramidal cells whose activity is

ABSTRACT: The spatial mapping theory of hippocampal function proposes that the rat hippocampus is specialized for navigational computations, computations that allow the animal to solve difficult spatial problems. In this paper, we review evidence obtained by recording place cells and other ‘‘spatially tuned’ ’ cells from freely moving rats. Our main conclusion is that the nature of the signals carried by these cells and the ways in which the signals transform after changing the environment imply that the hippocampus and associated structures are able to represent aspects of the geometry of the environment. Hippocampus 1999; 9:413–422. � 1999 Wiley-Liss, Inc. The ability of rats and mice to solve difficult navigational problems implies that they can form and use representations of their environment to select paths from their initial location to a goal (Tolman, 1948; Gallistel, 1990; Poucet, 1993). There are two very different ways in which such representations could be formed in the nervous system. On the one hand,

We present a model of the firing of place and head-direction cells in rat hippocampus. The model can predict the response of individual cells and populations to parametric manipulations of both geometric (e.g. O'Keefe & Burgess, 1996) and orientational (Fenton et al., 2000a) cues, extending a previous geometric model (Hartley et al., 2000). It provides a functional description of how these cells' spatial responses are derived from the rat's environment and makes easily testable quantitative predictions. Consideration of the phenomenon of remapping (Muller & Kubie, 1987; Bostock et al., 1991) indicates that the model may also be consistent with nonparametric changes in firing, and provides constraints for its future development.

Pattern separation, pattern completion, and new neuronal codes