Cognitive Neuroscience and the Study of Memory

Abstract

The neurosciences have grown rapidly over the last half century. This growth has been stimulated by two important developments. First, molecular biology has transformed cellular neurobiology and has led to a new conceptual framework for signaling, a molecular framework that encompasses not only signaling in nerve cells but in all the cells of the body. Second, work on brain and cognition, which was traditionally associated with a number of different disciplines, has merged into a single discipline: cognitive neuroscience. This has provided a new framework for the study of memory, perception, action, language, and perhaps even conscious awareness. In this review, we will consider the second development by focusing on one aspect of cognitive neuroscience: recent progress in memory research. In so doing, we also want to consider the broader question: to what degree can these two independent and disparate strands—molecular neurobiology and cognitive neuroscience—be united? Can molecular biology enlighten the study of cognitive processes, such as learning and memory, as it has other areas of biology, such as development? In turn, can cognitive neuroscience define novel phenomena that will lead to a completely new set of molecular mechanisms and insights? Cognitive neuroscience originated in two disciplines: in psychology, in the development of rigorous methods for analyzing behavior and cognition, and in systems neurobiology, in the effort to understand the structure and function of neuronal circuits of the sensory and motor systems of the brain. The fusion of these two disciplines was facilitated as well by the emergence of a coherent neuroscience—an interdisciplinary approach to the nervous system that encouraged the idea that the techniques and concepts of neurobiology and systems neuroscience might be usefully applied to the analysis of cognition. Until the beginning of the nineteenth century, the study of normal mental activity was a part of philosophy, and the chief method for understanding the mind was introspection. By the middle of the nineteenth century, introspection began to give way to experimental approaches that eventually led to the independent discipline of experimental psychology. In its early years, experimental psychology was concerned primarily with the study of sensation, but by the turn of the century the interests of psychologists turned to behavior itself—learning, memory, attention, perception, and voluntary action. The development of simple experimental methods for studying learning and memory—first in humans by Hermann Ebbinghaus in 1885 and a few years later in experimental animals by Ivan Pavlov and Edgar Thorndike—led to a rigorous empirical school of psychology called behaviorism. Behaviorists, notably James B. Watson and Burrhus F. Skinner, argued that behavior could be studied with the precision achieved in the physical sciences, but only if students of behavior abandoned speculation about what goes on in the mind (the brain) and focused instead on observable aspects of behavior. For behaviorists, unobservable mental processes, especially abstractions like perception, selective attention, and memory, were deemed inaccessible to scientific study. Instead, behaviorists concentrated on examining—objectively and precisely—the relationship between specific physical stimuli and observable responses in intact animals. Their early successes in rigorously studying simple forms of behavior, including learning, encouraged them to treat all processes that intervene between the stimulus (input) and behavior (output) as irrelevant to a scientific study of behavior. Thus, behaviorism largely ignored mental processes. As a result, the science of behavior was defined in terms of the limited techniques used to study it. This emphasis reduced the domain of experimental psychology to a restricted set of problems, and it excluded from study some of the most fascinating features of mental life. By the 1960s, it was not difficult for the founders of cognitive psychology—George Miller, Ulric Neisser, Herbert Simon, and others—to convince the scientific community of the narrowness of behaviorism. These early cognitive psychologists, building on the earlier evidence from Gestalt psychology, European neurology, and work by the British psychologist Frederic Bartlett, sought to demonstrate that our knowledge of the world is based on our biological apparatus for perceiving the world, and that perception is a constructive process dependent not only on the information inherent in a stimulus but also on the mental processing of the perceiver. Thus, cognitive psychology was concerned not simply with specifying the input and output for a particular behavior but also with analyzing the process by which sensory information is transformed into perception and action—that is, with evaluating how a stimulus leads to a particular behavioral response. In redirecting scientific attention to mental operations, cognitive ps