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

The head-direction (HD) cells found in the limbic system in freely moving rats represent the instantaneous head direction of the animal in the horizontal plane regardless of the location of the animal. The internal direction represented by these cells uses both self-motion information for inet-tially based updating and familiar visual landmarks for calibration. Here, a model of the dynamics of the HD cell ensemble is presented. The sta-bility of a localized static activity profile in the network and a dynamic shift mechanism are explained naturally by synaptic weight distribution components with even and odd symmetry, respectively. Under symmetric weights or symmetric reciprocal connections, a stable activity profile close to the known direc-tional tuning curves will emerge. By adding a slight asymmetry to the weights, the activity profile will shift continuously without 1

During slow wave sleep (SWS), traces of neuronal activity patterns from preceding behavior can be observed in rat hippocampus and neocortex. The spontaneous reactivation of these patterns is manifested as the reinstatement of the distribution of pairwise firing-rate correlations within a population of simultaneously recorded neurons. The effects of behavioral state [quiet wakefulness, SWS, and rapid eye movement (REM)], interactions between two successive spatial experiences, and global modulation during 200 Hz electroencephalographic (EEG) “ripples ” on pattern reinstatement were studied in CA1 pyramidal cell population recordings. Pairwise firing-rate correlations during often repeated experiences accounted for a significant proportion of the variance in these interactions in subsequent SWS or quiet wakefulness and, to a lesser degree, during SWS before the experience on a given day. The latter effect was absent for novel experiences, suggesting that a persistent memory trace develops with experience. Pattern The hippocampus is thought to play an important role in the acquisition and consolidation of certain forms of memory. Lesions of the hippocampus lead to a temporally graded retrograde amnesia, suggesting that the hippocampus plays a role in the initial encoding of a memory but that, with time, the memory becomes independent of the hippocampus (Scoville and Milner,

We describe here hippocampal cells that respond during whole-body motion when a monkey is moved on a remote-controlled robot-mounted platform in a cue-controlled test chamber (2 x 2 x 2 m). Some of these cells responded to linear motion, and others to axial rotation. Some of these cells responded when the same motion occurred without a view of the visual field. Such cells appeared to be driven by vestibular inputs. Other cells required a view of the visual field for their response, and these cells appeared to be driv-en by the visual motion relative to the monkey of the test chamber. Further evidence that this was the case was that some of the cells responded to rotation and linear motion of the test chamber while the monkey remained stationary. Oth-er cells responded to combinations of whole-body motion and a view of the environment.

The rat hippocampus contains cells that are characterized by location-specific firing. Previous work has shown that the angular position of hippocampal place cell firing fields is accurately controlled by the position of visual cues, suggesting that vision plays a important role in triggering place cell activity. However, a role for other types of information has also been suggested because place cell activity can be recorded while animals are moving in the darkness. In this study, we asked whether place fields can get established in rats that have never One of the most intriguing features of the rat hippocampus is the existence of place cells. First discovered by O’Keefe and Dostrovsky (1971), such cells, when recorded extracellularly from a freely moving rat, have the remarkable characteristic of being active only when the animal is in a specific region of its environment. Thus, a given place cell fires in a spatially delimited area

Hippocampal place cells show location-specific firing as an-imals locomote in an environment. A possible explanation for these place fields is that each cell is simply driven by environmental sensory inputs available in its field. This can-not provide the full explanation, however, since cells can maintain stable place fields even in the absence of reliable environmental orienting cues. This suggests the cells are also influenced by movement-related information, since this is the only available, ongoing indicator of current location when external orienting cues are not present. Two candidates for the movement-related information are vestibular activation, and visual motion. To test for these influences, place cells were recorded as animals locomoted in a cylindrical apparatus that was made so that its wall (painted with vertical black and white stripes) and floor could

A number of computational models of hippocampal place cells incorporate attractor neural network architecture to simulate key findings in the place cell literature, including the properties of pattern completion, firing in the absence of visual input, and nonlinear responses to environmental manipulations. To test for evidence of attractor dynamics, ensembles of place cells were recorded using multiple-tetrode techniques. After many days of experience in an environment with salient local surface cues on a circular track and salient distal landmarks on the wall, the local surface cues were rotated as a set in opposition to the distal landmarks. The amount of mismatch between the local and distal sets of cues varied from 45 to 180°. If place cells were parts of strong attractors, then their place fields should Principal neurons of the rat hippocampus fire selectively in restricted locations of an environment (O’Keefe and Dostrovsky, 1971; Muller et al., 1987). Debate continues over whether these place cells are best described as the neural substrate of a cognitive map of the environment (O’Keefe and Nadel, 1978) or as the components of a more general relational learning system (Cohen and Eichenbaum, 1993). One reason for the continued debate is that few rules have been defined that describe precisely the nature of the interactions between the myriad sources of input onto place cells. Although place cells can be controlled by visual landmarks (O’Keefe and Conway, 1978; Muller and Kubie, 1987), this control is not absolute, and idiothetic cues and local surface cues can exert control over the cells in nonlinear ways (Young et

Hippocampalspatialviewcellsfoundinprimatesrespond toaregionofvisualspacebeinglookedat,relativelyindependentlyof wherethemonkeyislocated.Ratplacecellshaveresponseswhich dependonwheretheratislocated.Weinvestigatethehypothesisthatin bothtypesofanimal,hippocampalcellsrespondtoacombinationof visualcuesinthecorrectspatialrelationtoeachother.Inrats,whichhave awidevisualfield,suchacombinationmightdefineaplace.Inprimates, includinghumans,whichhaveamuchsmallervisualfieldandafovea whichisdirectedtowardsapartoftheenvironment,thesamemechanism mightleadtospatialviewcells.Acomputationalmodelinwhichthe neuronsbecomeorganizedbylearningtorespondtoacombinationofa smallnumberofvisualcuesspreadwithinanangleofa30receptivefield resultedincellswithvisualpropertieslikethoseofprimatespatialview cells.Thesamemodel,butoperatingwithareceptivefieldof270, producedcellswithvisualpropertieslikethoseofratplacecells.Thusa commonhippocampalmechanismoperatingwithdifferentvisualreceptivefieldsizescouldaccountforsomeofthevisualpropertiesofboth placecellsinrodentsandspatialviewcellsinprimates.

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,

Abstract We review evidence for two distinct cognitive processes by which humans and animals represent the navigable environment. One process uses the shape of the extended 3D surface layout to specify the navigator’s position and orientation. A second process uses objects and patterns as beacons to specify the locations of signiWcant objects. Although much of the evidence for these processes comes from neurophysiological studies of navigating animals and neuroimaging studies of human adults, behavioral studies of navigating children shed light both on the nature of these systems and on their interactions.