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H Eichenbaum

Publications and source records attributed to H Eichenbaum.

At least 55 records · Page 3Linked to original sources
PubMed1997

Cues that hippocampal place cells encode: dynamic and hierarchical representation of local and distal stimuli.

Hippocampal place fields were recorded as rats explored a four-arm radial maze surrounded by curtains holding distal stimuli and with distinct local tactile, olfactory, and visual cues covering each arm. Systematic manipulations of the individual cues and their interrelationships showed that different hippocampal neurons encoded individual local and distal cues, relationships among cues within a stimulus set, and the relationship between the local and distal cues. Double rotation trials, which maintained stimulus relationships within distal and local cue sets, but altered the relationship between them, often changed the responses of the sampled neural population and produced new representations. After repeated double rotation trials, the incidence of new representations increased, and the likelihood of a simple rotation with one of the cue sets diminished. Cue scrambling trials, which altered the topological relationship within the local or distal stimulus set, showed that the cells that followed one set of controlled stimuli responded as often to a single cue as to the constellation. These cells followed the single cue when the stimulus constellation was scrambled, but often continued firing in the same place when the stimulus was removed or switched to respond to other cues. When the maze was surrounded by a new stimulus configuration, all of the cells either developed new place fields or stopped firing, showing that the controlled stimuli had persistent and profound influence over hippocampal neurons. Together, the results show that hippocampal neurons encode a hierarchical representation of environmental information.

Animals↗
PubMed1997

Declarative memory: insights from cognitive neurobiology.

The discovery of declarative memory as distinct from other forms of memory is a major recent achievement in cognitive science. Basic issues about the nature of declarative memory are considered in this review from the perspective of studies on its underlying brain mechanisms. These studies have shown that declarative memory is mediated by a specific brain system including areas of the cerebral cortex and hippocampal region that make distinct functional contributions to memory processing. These processing mechanisms mediate the organization of memories in ways that can support the special properties of declarative or explicit memory expression. Furthermore, the basic properties of declarative memory in human beings can be viewed as evolving from a capacity for organized memory representation and flexible memory expression in animals.

Animals↗
PubMed1996

Functional organization of the hippocampal memory system.

In humans declarative or explicit memory is supported by the hippocampus and related structures of the medial temporal lobe working in concert with the cerebral cortex. This paper reviews our progress in developing an animal model for studies of cortical-hippocampal interactions in memory processing. Our findings support the view that the cortex maintains various forms of memory representation and that hippocampal structures extend the persistence and mediate the organization of these codings. Specifically, the parahippocampal region, through direct and reciprocal interconnections with the cortex, is sufficient to support the convergence and extended persistence of cortical codings. The hippocampus itself is critical to the organization cortical representations in terms of relationships among items in memory and in the flexible memory expression that is the hallmark of declarative memory.

Animals↗
PubMed1996

Conservation of hippocampal memory function in rats and humans.

The hippocampus is critical to declarative memory in humans. This kind of memory involves associations among items or events that can be accessed flexibly to guide memory expression in various and even new situations. In animals, there has been controversy about whether the hippocampus is specialized for spatial memory or whether it mediates a general memory function, as it does in humans. To address this issue we trained normal rats and rats with hippocampal damage on non-spatial stimulus-stimulus associations, then probed the nature of their memory representations. We report here that normal rats demonstrated two forms of flexible memory expression, transitivity, the ability to judge inferentially across stimulus pairs that share a common element, and symmetry, the ability to associate paired elements presented in the reverse of training order. Rats with neurotoxic damage limited to the hippocampus demonstrated neither form of flexible expression, indicating that non-spatial declarative processing depends specifically on the hippocampus in animals as it does in humans.

Animals↗
PubMed1996

Is the rodent hippocampus just for 'place'?

The prominent view that the rodent hippocampus is dedicated to spatial memory has been challenged recently by observations that both limit the nature of hippocampal spatial representation and extend its scope beyond literal space. These findings reveal that the rodent hippocampus mediates memory representations on the basis of non-spatial, as well as spatial, relations among items in memory, and supports access to these memories in a variety of situations. Therefore, the defining features of hippocampal representation in rodents, as in humans, lie not in the modality of the information processed, but in the organization of the information that supports a capacity for flexible memory expression.

Animals↗
PubMed1996

Learning and memory for hierarchical relationships in the monkey: effects of aging.

Young and aged rhesus monkeys were tested on 2 versions of a transitive inference task measuring learning and memory for hierarchical relationships. Animals initially acquired 4 object discrimination problems arranged such that the relationship between the stimuli followed the hierarchy A > B > C > D > E. The second version of the task was similar but involved a series of 7 objects. Learning and memory for the hierarchical relationships were evaluated during probe trials in which novel pairs of nonadjacent items (e.g., B and D) were presented for a response. Standard task accuracy measures failed to distinguish young and aged subjects at any point in training. In contrast, response latency effects that are indicative of relational information processing in young monkeys were entirely absent in aged subjects. The findings highlight the value of a relational memory framework for establishing a detailed neuropsychological account of cognitive aging in the monkey.

Aging↗
PubMed1995

Selective damage to the hippocampal region blocks long-term retention of a natural and nonspatial stimulus-stimulus association.

Normal rats rapidly acquire and remember associations between nonspatial stimuli as expressed in the social transmission of food preferences. In the present study, rats with selective neurotoxic lesions including all subdivisions of the hippocampal region (hippocampus proper, dentate gyrus, and subiculum) normally acquired and briefly retained the food odor association as demonstrated by intact memory immediately after social training. However, long-term memory in these animals was severely impaired in contrast to strong 24-h retention by intact rats. More selective lesions to the hippocampus proper plus dentate gyrus alone, or the subiculum alone had no effect on memory at either test interval. These findings indicate that the hippocampal region is required for long-term retention of a nonspatial form of natural memory.

Animals↗
PubMed1995

Information coding in the rodent prefrontal cortex. I. Single-neuron activity in orbitofrontal cortex compared with that in pyriform cortex.

1. Extracellular spike activity was recorded from 1,942 single neurons in orbitofrontal cortex (OF) and 591 single neurons in pyriform cortex (PIR) over multiple sessions in rats performing an eight-odor discrimination task in which the stimulus sequence contained predictable associations between particular odor pairs. Neural firing patterns were examined in relation to task events in the current trial and variables associated with current sensory processing, events of recent past trials, and long-term associations involving the odor cues. 2. Overall, 34% of single neurons in OF and 30% of single neurons in PIR fired selectively during one or more salient trial events including trial initiation, odor sampling, performance of the discriminative response, and water consumption. The activity of other cells recorded in OF (13%) and PIR (10%) was suppressed for the duration of each trial. Although the proportion of some cell types differed between the two areas, the firing patterns of OF and PIR neurons were qualitatively indistinguishable. 3. Firing during odor sampling and the discriminative response was influenced by the identity of the current odor. Some cells fired selectively to a single odor, but most cells were coarsely tuned such that they fired to several of the eight odors to differing degrees consistent with previous reports. Considerable odor coding was observed in both OF and PIR. 4. Firing during trial initiation and odor sampling was also influenced by the identity and reward association of the odor presented in the immediately preceding trial. The influence of past odor identity and valence was observed in both OF and PIR. 5. Firing during trial events was also influenced by the acquired associations between odors and their assigned reward contingencies and between pairs of odors involved in predictive relationships. The reward valence of the current odor significantly influenced firing during odor sampling and the discriminative response; some cells responded preferentially to rewarded odors and others to nonrewarded odors. Firing during trial initiation and odor sampling reflected whether or not the odor in the current trial had been predicted by the odor in the preceding trial. In addition, firing during odor sampling reflected the expectation of reward in the following trial that could be inferred from the predictable associations between odors. Each of these properties was observed in both OF and PIR. 6. The findings in OF were consistent with the view that prefrontal subdivisions mediate the temporal organization of complex behaviors within specific informational domains. OF appears to be concerned with the specific domain of olfaction.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1995

Information coding in the rodent prefrontal cortex. II. Ensemble activity in orbitofrontal cortex.

1. Neural activity was recorded from the orbitofrontal cortex (OF) of rats performing an eight-odor discrimination task that included predictable associations between particular odor pairs. A modified linear discriminant analysis was employed to characterize the population response in each trial of the task as a point in an N-dimensional activity space with the firing rate of each cell in the population represented on one of the N dimensions. The ability of the ensemble to discriminate among conditions of a variable was reflected in the tendency of population responses to cluster together in this activity space for repetitions of a given condition. We assessed coding of several variables describing the period of odor sampling, focusing on aspects of current, past, and future events reflected in single-neuron firing patterns, in ensembles composed of 22-138 cells active during the period when the rats sampled the discriminative stimulus in each trial. 2. OF ensembles performed well at discriminating variables with relevance to task demands represented in single-neuron firing patterns, specifically the physical attributes and assigned reward contingency of the current odor as well as the expectation of reward in the following trial that could be inferred from the predictable associations between particular pairs of odors. OF ensembles were able to correctly identify the identity and assigned reward contingency of the current odor in up to 52% (chance = 12.5%) and 99% (chance = 50%) of all trials, respectively, such that the observed behavioral performance required a population of 5,364 odor-responsive cells in the case of odor identity and only 40 cells in the case of valence. Expectations regarding upcoming rewards based on both assigned response contingency and associations between particular pairs of odors were correctly classified in up to 67% (chance = 20%) of all trials such that the observed level of behavioral performance required a population of 3,169 cells. 3. Other information represented in the single-neuron firing patterns, such as the identity and reward contingency of the preceding odor and specific odor-odor associations, was poorly encoded by OF ensembles. Thus neural ensembles in OF may represent only some of the information reflected in single-neuron activity. Stable coding of only the most useful and relevant information by the ensemble might emerge from the tuning properties of single neurons under the influence of the task at hand, producing in the well-trained animal the observed pattern of broad and diverse coding by single neurons and selective, task-relevant coding by neural ensembles in OF.

Animals↗
PubMed1994

Correlates of hippocampal complex-spike cell activity in rats performing a nonspatial radial maze task.

The observation of hippocampal place cells forms a major line of evidence supporting the view that the hippocampus is dedicated to spatial processing. However, most studies demonstrating the spatial properties of hippocampal unit activity have employed tasks that emphasize spatial cues but minimize nonspatial cues. In the present experiment we recorded the activity of hippocampal complex-spike cells from rats performing a nonspatial radial maze task. Performance in this task was guided by local visual-tactile cues on the maze arms, while distal spatial cues were minimized and made irrelevant. The influence of three variables on unit activity was examined:type of cue on an arm, spatial location of an arm, and the relative position of the animal on an arm. Of the units recorded, almost one-fifth were classified as "cue cells" in that their activity was associated with cue type but not spatial location. Conversely, a similar proportion of the units were classified as "place cells" in that their activity was associated with location, but not cue type. In an additional similar proportion of units, firing was influenced only by relative position and not by local cues or spatial locations. For the majority of units, however, firing was related to combinations of these three variables, indicating that most hippocampal neurons encoded conjunctions or relations between spatial and local cue information. This pattern of results indicates that when local rather than distal spatial cues are emphasized, hippocampal neural activity is strongly influenced by salient nonspatial cues and shows no overwhelming predominance of place coding. These findings are at odds with the hypothesis that the hippocampus is selectively involved in spatial processing and, conversely, support the broader view that the hippocampus encodes both spatial and nonspatial relations among important experimental variables.

Action Potentials↗
PubMed1993

Critical role of the parahippocampal region for paired-associate learning in rats.

Human amnesics are severely impaired in learning arbitrary associations between word pairs. This report examines the role of the hippocampal system in an analog of paired-associate learning developed for rats. Subjects with selective damage to the parahippocampal region and controls were tested on an odor-guided paired-associate task. Normal rats readily learned to distinguish paired associates from various mispairings of the same odors, whereas most animals with parahippocampal damage failed to learn. Lesioned animals were, however, able to acquire correct responses to stimulus pairs for which an association between odors was not required. These findings extend the usefulness of olfactory learning as a model for studies of higher order learning capacity in rodents and indicate that in rats, as in humans, hippocampal areas are critical for learning arbitrary nonspatial relationships between stimuli.

Animals↗
PubMed1992

Neuronal activity in the hippocampus during delayed non-match to sample performance in rats: evidence for hippocampal processing in recognition memory.

Neuronal activity in the CA1 of rats was explored with regard to functional correlates of performance in an odor-guided continuous delayed non-match to sample task. Although different CA1 cells fired in association with each identifiable trial event, these analyses focused on cells that fired selectively during the period of odor cue sampling and response generation. The firing patterns of many of these cells reflected the match or non-match comparison between current and previous odor cues independent of the particular stimuli that composed those comparisons. Such cells were more prevalent in sessions when performance was highly accurate. Hippocampal cells did not demonstrate stimulus-evoked firing that persisted through the memory delay, nor did they fire differentially to session-novel vs. repeated odor presentations. These results suggest that the hippocampus contributes to recognition memory by processing comparisons between current information and representations of previous stimuli stored in parahippocampal and neocortical structures.

Animals↗