Précis of O'Keefe & Nadel's The hippocampus as a cognitive map

Sequential processing of “items” and “relations”

Eichenbaum et al. (1994a) hypothesized that perceptually distinct items and the relations among them are processed sequentially by the parahippocampal region and the hippocampal formation, respectively. Predictions based solely on their model's sequential-processing feature might prove easier to disconfirm than those based on its representational features. Two such predictions are discussed: (1) double dissociations should be impossible following hippocampal vs. parahippocampal lesions, and (2) hippocampal lesions should not exacerbate impairments that follow complete parahippocampal lesions.

Associations across time: The hippocampus as a temporary memory store

All recent memory theories of hippocampal function have incorporated the idea that the hippocampus is required to process items only of some qualitatively specifiahle kind, and is not required to process items of some complementary set. In contrast, it is now proposed that the hippocampus is needed to process stimuli of all kinds, but only when there is a need to associate those stimuli with other events that are temporally discontiguous. In order to form or use temporally discontiguous associations, it is essential to maintain some memory of the first component until the second component has occurred. When the temporal gap to he spanned is small, and the number of items to be temporarily retained is low, a limited-capacity, short-term store is sufficient to allow associations to be formed. Such a store is presumed to operate in parallel with the hippocampus in normal animals. Hippocampal damage disrupts a much higher-capacity store that has a slower decay rate, and so leaves animals with only a very limited ability to form temporally discontiguous associations. Hippocampal damage, however, is not held to affect the long-term storage of associations of any kind, if they can be formed. Analyses of both new and existing data are presented to show that by classifying tasks in terms of the need to use a temporary memory store to retain temporally discontiguous information one can cut right across existing classifications as well as achieve a better fit to the data. The hippocampus thus seems best described as a high-capacity, intermediate-term memory store.

Four frames suffice: A provisional model of vision and space

This paper presents a general computational treatment of how mammals are able to deal with visual objects and environments. The model tries to cover the entire range from behavior and phenomenological experience to detailed neural encodings in crude but computationally plausible reductive steps. The problems addressed include perceptual constancies, eye movements and the stable visual world, object descriptions, perceptual generalizations, and the representation of extrapersonal space.

The entire development is based on an action-oriented notion of perception. The observer is assumed to be continuously sampling the ambient light for information of current value. The central problem of vision is taken to be categorizing and locating objects in the environment. The critical step in this process is the linking of visual information to symbolic object descriptions; this is calledindexing, from the analogy of identifying a book from index terms. The system must also identifysituationsand use this knowledge to guide movement and other actions in the environment. The treatment focuses on the different representations of information used in the visual system.

The four representational frames capture information in the following forms: retinotopic, head-based, symbolic, and allocentric. The functional roles of the four frames, the communication among them, and their suggested neurophysiological realization constitute the core of the paper. The model is perforce crude, but appears to be consistent with all relevant findings.

Recovered consciousness: A proposal for making consciousness integral to neuropsychological theories of memory in humans and nonhumans

Why is consciousness associated with recovery of memories that are initially dependent on the hippocampal system? A hypothesis is proposed that the medial temporal lobe/hippocampal complex (MTL/H) receives as its input only information that is consciously apprehended. By a process termed “cohesion,” the MTL/H binds into a memory trace those neural elements that mediated the conscious experience so that effectively, “consciousness” is an integral part of the memory trace. It is the phenomenological records of events (Conway 1992), integrated consciousness-content packets, that are recovered when memory traces are retrieved.

Categories, life, and thinking

Classifying is a fundamental operation in the acquisition of knowledge. Taxonomic theory can help students of cognition, evolutionary psychology, ethology, anatomy, and sociobiology to avoid serious mistakes, both practical and theoretical. More positively, it helps in generating hypotheses useful to a wide range of disciplines. Composite wholes, such as species and societies, are “individuals” in the logical sense, and should not be treated as if they were classes. A group of analogous features is a natural kind, but a group of homologous features is not. Imposing hypotheses justified only on the basis of nominalist, realist, phenomenalist, or conceptualist metaphysics upon the neurophysiology of organisms or upon the causes of behavior exemplifies the “psychologist's fallacy” of William James. Levels should be distinguished from their members and from classes of levels, and the ontological status of entities ranked at levels should be made clear. It is important not to confuse such categories as substance and process with one another. Several genetical terms, such as “gene” and chromosome,” are even more equivocal than has been realized. Discussions about units of selection, behavior, and thinking suffer from the ambiguity of a “unit of” an entity. An important source of misunderstanding about natural selection is the habit of treating it as an “agent”: in an important sense, natural selection does not “act” at all.

The meaning of representation in animal memory

A representation is a remnant of previous experience that allows that experience to affect later behavior. This paper develops a metatheoretical view of representation and applies it to issues concerning representation in animals. To describe a representational system one must specify the following: the domain or range of situations in the represented world to which the system applies; the content or set of features encoded and preserved by the system; the code or transformational rules relating features of the representation to the corresponding features of the represented world; the medium, or the representation's physical instantiation; and the dynamics, or how the system changes with time. In part because of the behaviorist assumption that the hypothetical, covert changes occurring in an organism during learning correspond to the overt physical changes that are observed, issues of representation in animal behavior have been largely ignored as irrelevant or misleading. However, it can be inferred that representations, acting as models of environmental regularities, operate at many levels of behavioral functioning, both cognitive and noncognitive. Objections to the use of this concept in explanations of animal behavior, based on the claim that it is indeterminate and on behaviorist considerations of parsimony, can be answered. Animal representations may be specialized in terms of tasks and species. Data from tasks involving spatial memory, delayed matching-to-sample, and sequence learning suggest some foundations for a general theory of animal representations.

Multiple representations of space underlying behavior

We argue that a map is meaningless unless we have a process for using it. Thus, in this paper, we not only offer the world graph as a representation of relationships among situations the animal has encountered and may encounter again, but we also offer algorithms for how the information encoded in the world graph may be used by the animal in determining its behavior. Each node of the graph encodes a recognizable situation in the animal's world, but a given place may well be encoded in a number of different nodes. Nodes not only require algorithms for the recognition of the situation; they store information about drive reduction associated with the encoded situation. We note that the use of graphs as a basis for exploring some search space is well known in artificial intelligence (AI), but we stress the importance of the animal's exploration of its environment for growing the graph, as distinct from the mathematically described potential nodes frequent in AI search spaces. To explore a number of hypotheses about the way information in the world graph is used to guide the animal's movement, we recall a number of classical experiments on maze exploration by animals, and use them to argue for the nonlocal hypothesis (selection of a path does not depend only upon information about the immediate environment of the animal) and the competing nodes hypothesis (more than one drive may enter into the determination of the animal's behavior at any time). An important feature of the model is that it yields exploration and latent learning without the introduction of an exploratory drive. We also note that the performance exhibited by the model appears to be state-dependent when the animal operates under high drive levels. The drive-interaction matrix is offered as a subject for future research.

We complement the presentation of the world graph model, its drive dynamics, and how these are constrained by experiments on maze behavior, with a brief analysis of maps in the brain. We distinguish egocentric maps–which we relate to the many visual systems–from allocentric maps. We offer a somewhat unconventional view of short-term and long-term memory. We examine cooperative computation in somatotopically organized networks, relating this to visually guided behavior in the frog, and to the interaction of colliculus and cortex in the control of eye movements. We examine, but do not advocate, the hypothesis that the hippocampus is a cognitive map. We do stress that if it is a cognitive map, it must be seen as a chart of the local neighborhood, rather than the whole atlas; and we note that the cognitive map hypothesis would lead one to expect the region to exhibit activation of place cells before the animal leaves the previous place.

Reticulo-cortical activity and behavior: A critique of the arousal theory and a new synthesis

It is traditionally believed that cerebral activation (the presence of low voltage fast electrical activity in the neocortex and rhythmical slow activity in the hippocampus) is correlated with arousal, while deactivation (the presence of large amplitude irregular slow waves or spindles in both the neocortex and the hippocampus) is correlated with sleep or coma. However, since there are many exceptions, these generalizations have only limited validity. Activated patterns occur in normal sleep (active or paradoxical sleep) and during states of anesthesia and coma. Deactivated patterns occur, at times, during normal waking, or during behavior in awake animals treated with atropinic drugs. Also, the fact that patterns characteristic of sleep, arousal, and waking behavior continue in decorticate animals indicates that reticulo-cortical mechanisms are not essential for these aspects of behavior.

These puzzles have been largely resolved by recent research indicating that there are two different kinds of input from the reticular activating system to the hippocampus and neocortex. One input is probably cholinergic; it may play a role in stimulus control of behavior. The second input is noncholinergic and appears to be related to motor activity; movement-related input to the neocortex may be dependent on a trace amine.

Reticulo-cortical systems are not related to arousal in the traditional sense, but may play a role in the control of adaptive behavior by influencing the activity of the cerebral cortex, which in turn exerts control over subcortical circuits that co-ordinate muscle activity to produce behavior.

Hippocampus, delay neurons, and sensory heterogeneity

We raise three issues concerning the Eichenbaum, Otto & Cohen (1994) model. (1) We argue against the strict division of labor that Eichenbaum et al. attribute to neocortical and limbic regions. (2) We raise the possibility that the anterior and posterior portions of the hippocampus may be important for different types of information processing. (3) We argue that, rather than reflecting relational processing, different neural responses to “match” and “nonmatch” trials may relate to different required spatial responses.

The hippocampus seen in the context of declarative and procedural control

Various apparently incompatible theories of hippocampal function have been proposed but integration is now needed. It is argued that the involvement of the hippocampus is most clearly seen when the animal needs to extrapolate beyond current sensory information. Such control can involve both the initiation of behaviour in the absence of appropriate sensory input and the inhibition of behaviour that might otherwise be triggered by current sensory input.

A review of the verbal and visual memory impairments in children with foetal alcohol spectrum disorders

BACKGROUND

Children with Foetal Alcohol Spectrum Disorders (FASD) have significant impairments in memory, negatively affecting academics and daily functioning.

PRIMARY OBJECTIVE

To review published research on: (1) verbal and visual-spatial memory in children with FASD or prenatal alcohol exposure (PAE); (2) animal research on the impact of PAE on memory; and (3) brain areas involved in memory that are affected by PAE.

MAIN OUTCOMES

Verbal memory is one of the main areas of memory affected by gestational alcohol exposure, specifically in encoding and retrieving information. Spatial memory has emerged as a dominant deficit in individuals with FASD, consistent in children, adolescents and adults. There are regions of the brain more typically affected by PAE, which have ties to memory functioning. Animal research has confirmed the presence of impacts to key brain regions involved in memory functioning for those affected by PAE.

CONCLUSION

Memory deficits are a prevalent finding in individuals with PAE. Research in this area is complicated by small sample sizes, difficulty linking animal research to human application and lack of effective connection between existing memory theory and functional memory testing in FASD. New research has shown that there are implications for memory and learning amelioration in children with FASD.

Working Memory, Cues, and Wayfinding in Older Women

Individuals create cognitive maps based on relationships between cues in the environment. Older individuals are often impaired in wayfinding, especially in environments that lack distinctive features. This study examines how working memory ability in older women is related to wayfinding performance in the presence of salient (distinctive, prominent) or nonsalient cues. The degree of salient cue complexity is also examined, thus leading to the hypothesis that salient, complex cues are important in wayfinding and that working memory capacity is related to wayfinding performance. The virtual computer-generated arena is used to test this hypothesis in 20 healthy older women in three different environmental cue conditions varying in salience and complexity. Data analyses indicate that older women perform best in salient cue conditions. A greater working memory capacity is related to improved performance in the nonsalient cue condition. These findings offer preliminary evidence that cue salience is especially important in wayfinding.