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H Eichenbaum

Publications and source records attributed to H Eichenbaum.

At least 19 recordsLinked to original sources
PubMed2005

Neural correlates of social odor recognition and the representation of individual distinctive social odors within entorhinal cortex and ventral subiculum.

Recognition of individual conspecifics is important for social behavior and requires the formation of memories for individually distinctive social signals. Individual recognition is often mediated by olfactory cues in mammals, especially nocturnal rodents such as golden hamsters. In hamsters, this form of recognition requires main olfactory system input to the lateral entorhinal cortex (LEnt). Here, we tested whether neurons in LEnt and the nearby ventral subiculum (VS) would show cellular correlates of this natural form of recognition memory. Two hundred ninety single neurons were recorded from both superficial (SE) and deep layers of LEnt (DE) and VS while male hamsters investigated volatile odorants from female vaginal secretions. Many neurons encoded differences between female's odors with many discriminating between odors from different individual females but not between different odor samples from the same female. Other neurons discriminated between odor samples from one female and generalized across collections from other females. LEnt and VS neurons showed enhanced or suppressed cellular activity during investigation of previously presented odors and in response to novel odors. A majority of SE neurons decreased firing to odor repetition and increased activity to novel odors. In contrast, DE neurons often showed suppressed activity in response to novel odors. Thus, neurons in LEnt and VS of male hamsters encode information that is critical for the identification and recognition of individual females by odor cues. This study reveals cellular mechanisms in LEnt and VS that may mediate a natural form of recognition memory in hamsters. These neuronal responses were similar to those observed in rats and monkeys during performance in standard recognition memory tasks. Consequently, the present data extend our understanding of the cellular basis for recognition memory and suggest that individual recognition requires similar neural mechanisms as those employed in laboratory tests of recognition memory.

Action Potentials↗
PubMed2003

The perirhinal-entorhinal cortex, but not the hippocampus, is critical for expression of individual recognition in the context of the Coolidge effect.

The Coolidge effect is a phenomenon in which males show renewed sexual interest in a novel female following copulation to satiety with another female. In golden hamsters, this phenomenon depends on the ability to recognize conspecifics using chemosensory cues processed through the main olfactory system. Here we tested whether olfactory targets in the hippocampal system support this natural form of recognition memory. Male hamsters received ibotenic acid lesions of the perirhinal-entorhinal cortex (PR-ENT) or hippocampus (H) and were allowed to copulate to satiety with a female conspecific, then were presented with two anesthetized females, the familiar mate and an unfamiliar female that copulated with another male. Sham-operated and H-lesioned subjects preferentially investigated the novel female, indicating intact recognition of individual identity. By contrast, PR-ENT-lesioned males failed to discriminate familiar and novel females, and this deficit could not be attributed to abnormal copulatory behavior during mating. All subjects were able to detect and discriminate between female odors when presented in isolation during a habituation-discrimination test, indicating that behavioral deficits shown by PR-ENT males were not due to anosmia or a general investigatory deficit. Thus, the perirhinal-entorhinal cortex, but not the hippocampus, is critical for the recognition of familiar conspecifics in this naturalistic situation. This study reveals an essential role for the perirhinal-entorhinal cortex, but not the hippocampus, in a natural form of recognition memory within the social behavior of hamsters. The findings show a strikingly similar pattern to the effects of selective damage to the same brain regions on performance in standard recognition memory tasks by rats and monkeys. Therefore, the present data extend our understanding of the differential role of structures of the hippocampal memory system, showing continuity across species and between formal laboratory tests and the function of memory in natural social behavior.

Animals↗
PubMed2001

The hippocampus and declarative memory: cognitive mechanisms and neural codes.

It is widely accepted that the hippocampus and related brain areas mediate declarative (or explicit) memory in humans. However, little is known about the fundamental cognitive mechanisms of hippocampal dependent memory or about the nature of hippocampal neural representations that underlie properties of declarative memory. Here, it is proposed that the hippocampus plays a critical role, when distinct personal experiences must be encoded in relation to one another and linked within an organization that supports flexible, inferential memory expression. This set of fundamental cognitive mechanisms is consistent with key properties of declarative memory as observed in humans. Furthermore, emerging evidence from recordings of hippocampal neural activity shows that hippocampal networks encode episodic memories as sequences of events and the places, where they occur. In addition, hippocampal neuronal networks encode events and places that are common across related episodes. This combination of coding properties suggests that the hippocampus contributes to declarative memory by mediating the construction of a "memory space" composed of a network of linked episodic representations.

Cognition↗
PubMed2001

CA1-specific N-methyl-D-aspartate receptor knockout mice are deficient in solving a nonspatial transverse patterning task.

In both humans and animals, the hippocampus is critical to memory across modalities of information (e.g., spatial and nonspatial memory) and plays a critical role in the organization and flexible expression of memories. Recent studies have advanced our understanding of cellular basis of hippocampal function, showing that N-methyl-d-aspartate (NMDA) receptors in area CA1 are required in both the spatial and nonspatial domains of learning. Here we examined whether CA1 NMDA receptors are specifically required for the acquisition and flexible expression of nonspatial memory. Mice lacking CA1 NMDA receptors were impaired in solving a transverse patterning problem that required the simultaneous acquisition of three overlapping odor discriminations, and their impairment was related to an abnormal strategy by which they failed to adequately sample and compare the critical odor stimuli. By contrast, they performed normally, and used normal stimulus sampling strategies, in the concurrent learning of three nonoverlapping concurrent odor discriminations. These results suggest that CA1 NMDA receptors play a crucial role in the encoding and flexible expression of stimulus relations in nonspatial memory.

Animals↗
PubMed2000

Hippocampus: mapping or memory?

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.

Animals↗
PubMed2000

Neural correlates of olfactory recognition memory in the rat orbitofrontal cortex.

The orbitofrontal cortex (OF) is strongly and reciprocally connected with the perirhinal (PR) and entorhinal areas of the medial temporal lobe and plays an important role in odor recognition memory. This study characterized firing patterns of single neurons in the OF of rats performing a continuous odor-guided delayed nonmatch to sample (DNMS) task. Most OF neurons fired in association with one or more task events, including the initiation of trials, the sampling of odor stimuli, and the consumption of rewards. OF neurons also exhibited sustained odor-selective activity during the memory delay, and a large proportion of OF cells had odor-specific enhanced or suppressed responses on stimulus repetition. Most OF neurons were activated during several task events, or associated with complex behavioral states. The incidence of cells that fired in association with the critical match/non-match judgement was increased as the DNMS rule was learned, and was higher in OF than in perirhinal and entorhinal cortex. Furthermore, the classification of match and nonmatch trials was correlated with accuracy in performance of that judgement. These findings are consistent with the view that OF is a high order association cortex that plays a role both in the memory representations for specific stimuli and in the acquisition and application of task rules.

Action Potentials↗
PubMed2000

Neurotoxic hippocampal lesions have no effect on odor span and little effect on odor recognition memory but produce significant impairments on spatial span, recognition, and alternation.

Recent work has shown that lesions of the hippocampus in monkeys cause deficits in the capacity to remember increasing numbers of objects, colors, and spatial locations (). However, others have observed that hippocampectomized monkeys can show intact memory for a list of objects or locations (). We wished to explore the effects of hippocampal damage on the capacity of memory in the rodent and, to do so, developed novel "span" tasks in which a variable number of odors or locations had to be remembered. In the odor span task (experiment 1), rats were trained on a nonmatching to sample task in which increasing numbers of odors had to be remembered. Half of the trained rats received ibotenic acid lesions of the hippocampus. Postoperatively, hippocampectomized animals did not differ from control animals even when required to remember up to 24 odors. However, when tested on delayed retention of a list of 12 odors, rats with hippocampal lesions were impaired at a long delay. Also, these rats were impaired on a subsequent test of delayed spatial alternation. In a spatial span task (experiment 2), naive rats were trained on a nonmatching to sample task in which a variable number of locations had to be remembered. After this, half of the animals received ibotenic acid lesions. Postoperatively, hippocampectomized animals performed above chance levels when required to remember a single cup location, but were unable to remember more. Subsequent testing on another spatial delayed alternation task suggested that hippocampectomized rats could recognize, but could not inhibit their approach to previously visited locations.

Animals↗
PubMed2000

Hippocampal neurons encode information about different types of memory episodes occurring in the same location.

Firing patterns of hippocampal complex-spike neurons were examined for the capacity to encode information important to the memory demands of a task even when the overt behavior and location of the animal are held constant. Neuronal activity was recorded as rats continuously alternated left and right turns from the central stem of a modified T maze. Two-thirds of the cells fired differentially as the rat traversed the common stem on left-turn and right-turn trials, even when potentially confounding variations in running speed, heading, and position on the stem were taken into account. Other cells fired differentially on the two trial types in combination with behavioral and spatial factors or appeared to fire similarly on both trial types. This pattern of results suggests that hippocampal representations encode some of the information necessary for representing specific memory episodes.

Action Potentials↗
PubMed2000

A cortical-hippocampal system for declarative memory.

Recent neurobiological studies have begun to reveal the cognitive and neural coding mechanisms that underlie declarative memory--our ability to recollect everyday events and factual knowledge. These studies indicate that the critical circuitry involves bidirectional connections between the neocortex, the parahippocampal region and the hippocampus. Each of these areas makes a unique contribution to memory processing. Widespread high-order neocortical areas provide dedicated processors for perceptual, motor or cognitive information that is influenced by other components of the system. The parahippocampal region mediates convergence of this information and extends the persistence of neocortical memory representations. The hippocampus encodes the sequences of places and events that compose episodic memories, and links them together through their common elements. Here I describe how these mechanisms work together to create and re-create fully networked representations of previous experiences and knowledge about the world.

Animals↗
PubMed2000

The neurophysiology of memory.

How do the structures of the medial temporal lobe contribute to memory? To address this question, we examine the neurophysiological correlates of both recognition and associative memory in the medial temporal lobe of humans, monkeys, and rats. These cross-species comparisons show that the patterns of mnemonic activity observed throughout the medial temporal lobe are largely conserved across species. Moreover, these findings show that neurons in each of the medial temporal lobe areas can perform both similar as well as distinctive mnemonic functions. In some cases, similar patterns of mnemonic activity are observed across all structures of the medial temporal lobe. In the majority of cases, however, the hippocampal formation and surrounding cortex signal mnemonic information in distinct, but complementary ways.

Animals↗
PubMed1999

The hippocampus: The shock of the new.

Recent successes in functional brain imaging have suggested that the hippocampus is part of a novelty-detection network; but consideration of the available evidence and of the cognitive demands of novelty processing suggests that things are not so simple.

Animals↗
PubMed1999

The global record of memory in hippocampal neuronal activity.

In humans the hippocampal region of the brain is crucial for declarative or episodic memory for a broad range of materials. In contrast, there has been controversy over whether the hippocampus mediates a similarly general memory function in other species, or whether it is dedicated to spatial memory processing. Evidence for the spatial view is derived principally from the observations of 'place cells'-hippocampal neurons that fire whenever the animal is in a particular location in its environment, or when it perceives a specific stimulus or performs a specific behaviour in a particular place. We trained rats to perform the same recognition memory task in several distinct locations in a rich spatial environment and found that the activity of many hippocampal neurons was related consistently to perceptual, behavioural or cognitive events, regardless of the location where these events occurred. These results indicate that nonspatial events are fundamental elements of hippocampal representation, and support the view that, across species, the hippocampus has a broad role in information processing associated with memory.

Animals↗