Search Results

This chapter considers a number of prominent theories of hippocampal function that have been developed from work on animals. Two theories have dominated research on hippocampal function over the past quarter century. The first is that it is involved in the formation of memories for everyday facts and events that can be consciously recalled—collectively called declarative memory. The other major theory emerging from observations first made during the recording of single-cell activity in freely moving rodents is the idea that it is involved in spatial memory and, more specifically, the formation of cognitive maps and their use in navigation through space. A range of alternative theories, particularly those built around how memory systems handle ambiguity, associative-relations, and context, are also discussed. The chapter concludes by zeroing in on the idea that neural activity in the hippocampal formation contributes to episodic memory.

This chapter focuses on the role of the declarative memory system in a cognitive architecture. Declarative memory contains the knowledge that gives each of us our identities and the ability to behave flexibly in the world. Our brains, particularly the temporal structures around the hippocampus, impose severe limitations on our ability to maintain memories in highly flexible forms. The basic characteristics of declarative memory can be seen as arising from the need to balance this structural limitation against this functional need of adapting to environment demands. The chapter reviews a convergence of behavioral and brain imaging data concerned with the fan effect, and then looks at some examples of the pervasive application of these flexible declarative memories.

This chapter reviews cases of amnesia and evidence from functional brain imaging to provide insights about the nature of memory supported by the hippocampal memory system. The case of the famous amnesic patient H. M. show that memory can be distinguished from other psychological faculties. Furthermore, studies on H. M. distinguish declarative memory, which was severely impaired in his case, and spared working memory and non-memory perceptual, motor, and cognitive capacities. In addition, H. M. and other patients with damage to the hippocampal region had several preserved learning capacities including intact perceptual learning, motor skill learning, cognitive skill learning, pattern classification learning, classical conditioning of motor reflexes, and repetition priming. Thus, his memory impairment has been characterized as a deficit in explicit, declarative, or relational memory. Parallel studies using functional imaging of the brain have shown that the hippocampus is activated during encoding and retrieval in declarative memory.

This chapter discusses the four types of memory and the brain mechanisms that are important in storing them. These are working memory, declarative memory, procedural memory, and semantic memory. Working memory is a temporary store. To keep information there, the person must actively rehearse the information that is being stored and prevent distraction. Declarative memory stores “what, where, and when” information. Declarative memories may be verbal (e.g., recalling names) or nonverbal (e.g., recalling faces) and old (remote) or new (recent). Verbal declarative and semantic memories are stored in the left hemisphere and visual spatial memories are stored in the right hemisphere. Procedural memories are “how” memories.

This chapter reviews evidence from animal models of amnesia. The efforts to model amnesia associated with damage to the medial temporal lobe followed two parallel approaches, one using monkeys as the experimental subjects and the other using primarily rats. The studies on monkeys began appropriately by reproducing the same pervasive medial temporal damage that occurred in H. M. The early studies on rats focused on the hippocampus, leaving out of the experimental ablation other structures that were damaged in H. M. and in experiments on monkeys. The combined results of experiments testing provide compelling evidence for a comprehensive account of the cognitive mechanisms of declarative memory. Various kinds of learning, spatial and nonspatial, simple and complex, can be accomplished independent of the hippocampus in animals, as indeed is the case in human amnesic patients as well. However, the hippocampus is required to link together the representations of overlapping experiences into a relational representation and supports the flexible and inferential expression of indirect associations among items within that larger organization of linked memories.

Early memory development, particularly in the first two years of life, is quite remarkable indeed. Infants go from being able to remember single actions over a twenty-four-hour period to remembering more complex action sequences for up to three months, and later, to being able to remember sequences for up to a year. Of course, it is not simply the quantitative aspects of memory that change as infants develop, but the qualitative components of early memory also. That is, older infants not only acquire information more rapidly than younger infants, and retain that information over longer intervals, but they also encode more and different features from the stimulus array than their younger counterparts and can use these richer memories more flexibly across different contexts. This chapter examines the neurobiological developments that are correlated with these changes in memory. Topics discussed include the neural underpinnings of nondeclarative and declarative memory development, interconnectivity and the temporal-cortical network, and later developments in the neural substrates of declarative memory.

This chapter discusses various forms of binding fragments represented in multiple neocortical zones in different memory tasks and their event-related potential (ERP) correlates. Declarative memory binding and cross-cortical storage are discussed as critical components of episodic memory.

Studies on the amnesic patient H.M. began the modern era of the cognitive neuroscience of memory. These studies, and other case studies, showed that damage limited to the hippocampal region results in an impairment that is selective to memory and spares other perceptual, motor, emotional, or cognitive functions. Furthermore, the amnesic deficit is selective to the permanent establishment of new declarative memories. Thus H.M. and other patients with hippocampal damage have intact short-term and working memory, and can form long-term memories that do not rely on remembering specific past events or on the flexible use of memories to solve new problems. These and other characteristics of amnesia following hippocampal damage indicate that the hippocampal memory system is essential to relational memory, the ability to associate multiple events with one other and with their spatial and temporal context, and the ability to integrate many memories into a network of knowledge.

This chapter focuses on declarative memory consolidation at the human brain system level and recent advances in characterizing the neural underpinnings of this fundamental mnemonic operation. It provides a short overview of three lines of research on memory consolidation: one investigating the nature and duration of retrograde amnesia in brain damaged patients, one testing the vulnerability of memories to electroconvulsive therapy, and another probing the effect of sleep on forgetting curves.

The hippocampus must be considered in the context of how it performs its functions within the larger system of brain structures of which it is a part. Indeed, the hippocampus is only one of several structures that compose the full brain system that mediates declarative memory. This chapter identifies the main components of this system, outlines the anatomical pathways by which information flows through the system, and characterizes the functional contributions of its different components.

This chapter reviews evidence from studies of amnesia in humans. It provides a detailed overview of the case of H. M., to provide a closer perspective on the nature of his amnesia. H. M. was an epileptic for several years when, in an effort to alleviate his disorder, his medial temporal lobe area was removed. The surgery did indeed reduce the frequency of his seizures considerably — however, he had become severely amnesic. The chapter then explores the distinction between declarative and procedural memory, using several examples from the experimental literature on amnesia.

The function of the hippocampus must be considered in the context of the larger system of brain structures of which it is a part. Indeed, the hippocampus is only one of several structures that compose the full brain system that mediates declarative memory. This chapter identifies the main components of this system, outlines the anatomical pathways by which information flows through the system, and characterizes the functional contributions of its components.

Multiple memory systems describes how memories can be declarative or non-declarative; incentive learning produces one type of non-declarative memory. Patients with bilateral hippocampal damage have declarative memory deficits (amnesia) but intact non-declarative memory; patients with striatal dysfunction, for example, Parkinson’s patients who lose striatal dopamine have impaired incentive learning but intact declarative memory. Rats with lesions of the fornix (hippocampal output pathway), but not lesions of the dorsal striatum, have impaired spatial (declarative) memory; rats with lesions of the dorsal striatum, but not fornix, have impaired stimulus–response memory that relies heavily on incentive learning. These memory systems possibly inhibit one another to control responding: in rats, a group that received fornix lesions and had impaired spatial learning did better on an incentive task; in humans, hippocampus damage was associated with improvement on an incentive learning task and striatal damage was associated with increased involvement of the hippocampus in a route-recognition task.

This chapter summarizes electrophysiological studies of declarative memory formation using depth electrodes implanted in the medial temporal lobe (MTL) in epilepsy patients prior to epilepsy surgery. This experimental approach provides a unique opportunity to monitor quasi-normal human brain activity directly, in real time, within distinct MTL subcomponents and with a signal-to-noise ratio far superior to any other neuroimaging technique currently available. The results show that invasive electrophysiology can both localize and characterize brain processes that are important in determining what is remembered and what is forgotten. Insights into the temporal organization of memory formation and the interaction that occurs between substructures of the MTL during this mnemonic operation are described.

This chapter provides a detailed overview of a patient called H.M., in order to provide a closer perspective on the nature of his amnesia. It explores the distinction between declarative and procedural memory using several examples from the experimental literature on amnesia. H.M. had been severely epileptic for several years. In an effort to alleviate his disorder, the medial temporal lobe area was removed, and the surgery did reduce the frequency of his seizures considerably. However, following the surgery this patient became severely amnesic, and yet showed hardly any other neurological deficits.

In this chapter, the third fundamental functionality of the brain is examined: Memory. After a short presentation of the nature of memory and of its fundamental features, the chapter introduces the relevant neural mechanisms. This will allow us to deal with the fundamental difference between procedural and declarative memory, which turns out to be connected with two different functions, namely learning and memory. Finally, the problem of the stages of memory consolidation is discussed, starting with the traditional distinction between a short-term and a long-term memory. It shall be seen that it is convenient to establish a dichotomy between active and inactive memory.

It has long been known that the medial temporal lobe (MTL) is critical for conscious, or declarative, memory. However, debate continues to surround the precise role of the neural components of this region. The MTL is comprised of several interconnected structures known to be involved in memory, including the hippocampus and the entorhinal, perirhinal, and parahippocampal cortices. Recent evidence suggests that these different structures may make functionally dissociable contributions to memory processes. This chapter considers the distinction between different forms of declarative memory and reviews the current evidence regarding the specific role of the hippocampus in these processes.