摘錄

Chapter One Introduction Mind, Brain, and Experience THE DEVELOPING MIND AND HUMAN RELATIONSHIPS The mind emerges from the activity of the brain, whose structure and function are directly shaped by interpersonal experience. This book explores how recent findings from the study of human development and neurobiology can bring us to a new understanding of the developing mind.     There are many views from science on how the mind functions, providing in-depth but distinct perspectives on human experience. For example, neuroscience can inform us about how the brain gives rise to mental processes such as memory and perception. Developmental psychology offers us a view of how children's minds grow within families across time. Psychiatry gives us a clinical view of how individuals may suffer from emotional and behavioral disturbances that profoundly alter the course of their lives. Often these disciplines function in isolation from one another. Yet, when one attempts to synthesize their recent findings, an incredible convergence of many of these independent fields of study is revealed. These findings shed light on how the mind emerges from the substance of the brain as it is shaped by interpersonal relationships. My aim is to provide an overview and integration of some of these scientific perspectives, in order to build a foundation for a neurobiology of interpersonal experience.     The ideas of this framework are organized around three fundamental principles: 1. The human mind emerges from patterns in the flow of energy and information within the brain and between brains. 2. The mind is created within the interaction of internal neurophysiological processes and interpersonal experiences. 3. The structure and function of the developing brain are determined by how experiences, especially within interpersonal relationships, shape the genetically programmed maturation of the nervous system. In other words, human connections shape the neural connections from which the mind emerges.     What is the mind? There is an entity called the "mind" that is as real as the heart or the lungs or the brain, though it cannot be seen with or without a microscope. The foundation of the mind parallels a dictionary definition of the psyche: "1. the human soul; 2. the intellect; 3. psychiatry--the mind considered as a subjectively perceived, functional entity, based ultimately upon physical processes but with complex processes of its own: it governs the total organism and its interaction with the environment."     Because it reveals the connection between brain structure and function, current neuroscience provides us with new insights into how experience shapes mental processes. By altering both the activity and the structure of the connections between neurons, experience directly shapes the circuits responsible for such processes as memory, emotion, and self-awareness. We can use an understanding of the impact of experience on the mind to deepen our grasp of how the past continues to shape present experience and influence future actions. Insights into the mind, brain, and experience can provide a window into these connections across time, allowing us to see human development in a four-dimensional way.     This book attempts to synthesize concepts and findings from a range of scientific disciplines, including those studying attachment, child development, communication, complex systems, emotion, evolution, information processing, memory, narrative, and neurobiology. I have attempted to provide enough of an introduction for those who may be totally unfamiliar with these domains to be able to understand the material and apply the relevant findings in their professional work and personal lives. When we examine what is known about how the mind develops, we can gain important insights into the ways in which people can continue to grow throughout life. The mind does not stop developing even as we grow past childhood and adolescence. Through understanding the connections between mental processes and brain functioning, we can build a neurobiological foundation for the ways in which interpersonal relationships--both early in life and throughout adulthood--continue to play a central role in shaping the emerging mind. ENERGY AND INFORMATION The mind--the patterns in the flow of energy and information--can be described as emanating from the activity of the neurons of the brain. Several different measures of forms of energy can be used to study these. Brain imaging studies examine the metabolic, energy-consuming processes in specific neural regions, or the blood flow to certain areas that are thought to be a clustering of localized neuronal activity. Electroencephalograms (EEGs) assess the electrical activity across the surface of the brain as measured by electrodes on the head. These assessments of "energy flow" are not popularized, unscientific views of the flow of some mysterious energy through the universe. Neuroscience studies the way in which the brain functions through the energy-consuming activation of neurons. The degree and localization of this arousal and activation within the brain--this flow of energy--directly create our mental processes.     But the mind is more than the flow of energy across time within the brain. The mind is also about the flow of information.     The mind has distinct modes of processing information. For example, our sensory systems can respond to stimuli from the outside world, such as sights or sounds, and can "represent" this information as patterns of neural firing that serve as mental symbols. The activity of the brain creates "representations" of various types of information about the outer and inner worlds. For example, we have representations of sensations in the body, of perceptions from our five senses, of ideas and concepts, and of words. Each of these forms of representation is thought to be created in different circuits of the brain. These information-processing modes can act independently, and also have important interactions with one another that directly affect their processing. We can have complex representations of sensations, perceptions, ideas, and linguistic symbols as we think, for example, of some time in the past. The integration of these distinct modes of information processing into a coherent whole may be a central goal for the developing mind across the lifespan.     Interpersonal relationships may facilitate or inhibit this drive to integrate a coherent experience. Relationships early in life may shape the very structures that create representations of experience and allow a coherent view of the world: Interpersonal experiences directly influence how we mentally construct reality. This shaping process occurs throughout life, but is most crucial during the early years of childhood. Patterns of relationships and emotional communication directly affect the development of the brain. Studies in animals, for example, have demonstrated that even short episodes of maternal deprivation have powerful neuroendocrine effects on the ability to cope with future stressful events. Studies of human subjects reveal that different patterns of child-parent attachment are associated with differing physiological responses, ways of seeing the world, and interpersonal relationship patterns. The communication of emotion may be the primary means by which these attachment experiences shape the developing mind. Research suggests that emotion serves as a central organizing process within the brain. In this way, an individual's abilities to organize emotions--a product, in part, of earlier attachment relationships--directly shapes the ability of the mind to integrate experience and to adapt to future stressors. THE ORGANIZATION OF THE BOOK The book is composed of two general forms of information. The scientific findings from a range of disciplines are summarized and synthesized to construct a conceptual foundation for an "interpersonal neurobiology" of the developing mind. This scientific foundation creates a new, interdisciplinary view of established knowledge. Conceptual implications and new proposals that are derived from data, clinical experience, and synthetic reasoning across disciplines can then be drawn from this framework.     Each chapter explores a major domain of human experience: memory, attachment, emotion, representation, states of mind, self-regulation, interpersonal connection, and integration. Presenting the information in this sequence allows for an overview of how experience shapes the mind in the discussions of memory and attachment before the related topics of emotion and representation are addressed. The more elaborated processes of states of mind and complex systems naturally follow and prepare us for a detailed discussion of the ways in which the mind develops the capacity to organize its functioning within self-regulation, patterns of interpersonal connection, and mental integration. Memory In Chapter 2, research in various forms of memory is summarized in order to help us understand how our earliest experiences in life shape not only what we remember, but how we remember and how we shape the narrative of our lives. Memory can be seen as the way the mind encodes elements of experience into various forms of representation. As a child develops, the mind begins to create a sense of continuity across time, linking past experiences with present perceptions and anticipations of the future. Within these representational processes, generalizations or mental models of the self and the self with others are created; these form an essential scaffold in which the growing mind interacts with the world.     One way in which the mind attempts to integrate these varied representations and mental models is within the narrative process. Autobiographical narratives are reviewed, in order to explore how the mind creates coherence within its own processes and how this central integrative function influences the nature of interpersonal relationships. In part, such an integrative function reveals the capacity of the mind to represent and process the activity of the minds of both self and others. Such a capacity appears to be central to secure attachment relationships. Attachment This overview of the mind, memory, and autobiographical narrative sets the stage for examining attachment in children as well as in adults in Chapter 3. Repeated patterns of children's interactions with their caregivers become "remembered" in the various modalities of memory and directly shape not just what children recall, but how the representational processes develop. Behavior, emotion, perceptions, sensations, and models of others are engrained by experiences that occur before children have autobiographical memory processes available to them. These implicit elements of memory also later influence the structure' of autobiographical narratives, which have been found to differ dramatically across the various attachment patterns.     A profound finding from attachment research is that the most robust predictor of a child's attachment to parents is the way in which the parents narrate their own recollections of their childhood experiences. This implies that the structure of an adult's narrative process--not merely what the adult recalls, but how it is recalled--is the most powerful feature in predicting how an adult will relate to a child. Studies of couples expecting their first child can predict how each parent will relate to their yet-to-be-born infant by examining the nature of the narratives of their own childhoods. The practical relevance of this finding is explored, along with other important discoveries from the field of adult attachment. These attachment studies provide a framework for understanding how communication within relationships facilitates the development of the mind. Emotion The primary ingredient of secure attachment experiences is the pattern of emotional communication between child and caregiver. This finding raises the fundamental question of why emotion is so important for the evolving identity and functioning of a child, as well as in the establishment of adult relationships.     Chapter 4 further explores the role of emotion in shaping interpersonal relationships and the human mind. What is emotion? Why does a child require emotional communication and the alignment of emotional states in order to allow for healthy development? To attempt to answer these questions fully, we need to synthesize a number of independent perspectives. The way the mind establishes meaning--the way it places value or significance on experience--is closely linked to social interactions. This connection between meaning and interpersonal experience occurs because these two processes appear to be mediated via the same neural circuits responsible for initiating emotional processes. Research into the nature of emotion serves as the foundation of a synthetic framework for understanding its central role in creating our subjective and our interpersonal experiences. Representations In Chapter 5, the way the mind creates mental representations of experience is reviewed in detail. Emotion can be seen as the fundamental process of the mind that links states of arousal with the appraisal of the value or the meaning of its own representational processes. In this way, the mind's creation of representations provides us with insight into how reality is shaped by emotional and interpersonal processes. Our internal experiences are constructive processes; our interpersonal relationships help shape the ways in which these representational processes develop. Emotion can thus be seen as an integrating process that links the internal and interpersonal worlds of the human mind.     From the beginning of life, the brain has an asymmetry in its circuitry, which leads to the specialization of functions on each side of the brain. The ways in which the mind creates representations of experience is shaped by this lateralization of function. The capacities to sense another person's emotions, to understand others' minds, and even to express one's own emotions via facial expressions and tone of voice are all mediated predominantly by the right side of the brain. In certain insecure attachment patterns, communication between parent and child may lack these aspects of emotions and mental experience. In contrast, secure attachments seem to involve the sharing of a wide range of representational processes from both sides of the brain. In essence, such balanced interpersonal communication allows the activity of one mind to sense and respond to the activity of another. Such sharing of activity can be seen as the sharing of states of mind, the topic of the next chapter. States of Mind Chapter 6 examines how different mental processes are organized within a state of mind. These states allow disparate activities of the brain to become cohesive at a given moment in time. A single brain functions as a system that can be understood by examining the "theory of nonlinear dynamics of complex systems," or, more briefly, "complexity theory." This perspective has been applied to a range of inanimate and living systems in an attempt to understand the often unpredictable but self-organizing nature of complex clusters of entities functioning as a system. The human brain has recently been examined by a number of theoreticians as one such system. Chapter 6 reviews these ideas and then proposes how the laws of such complex systems can be applied not only to the single mind, but to the functioning of two or more minds acting as a single system. This new application allows us to deepen our earlier discussion of states of mind and their fundamental importance in both creating internal subjective experience and shaping the nature of human relationships. Self-Regulation Chapter 7 then explores self-regulation--the way the mind organizes its own functioning--by examining how complex systems, such as the mind and interpersonal relationships, regulate the flow of their states by various means. Self-regulation is fundamentally related to the modulation of emotion. As we'll see, this process involves the regulation of the flow of energy and information via the modulation of arousal and the appraisal of meaning of cognitive representations of experience. Emotion regulation is initially developed from within interpersonal experiences in a process that establishes self-organizational abilities. Interpersonal Connection Chapter 8 examines the nature of the connections between minds. Interpersonal relationships shape the mind by allowing new states to emerge within interactions with others. Though relationships early in life shape the structural development of the brain, the mind appears to be open to ways in which interpersonal experience continues to facilitate development throughout the lifespan. Examples from families and individual patients in psychotherapy are offered to illustrate these ideas by examining how patterns of communication between parent and child help determine the ways in which self-regulation emerges early in development. These patterns can help us to understand how relationships throughout life may facilitate emotional well-being. Self-organization thus emerges out of self-other interactions. Integration At a given time, a state of mind creates cohesion within the various mental processes that define it. Mental states reflect specific patterns of activity, such as states of anger or shame. Some of these states become engrained over time with characteristic patterns of activity. These states can be seen as "self-states." How the self creates a sense of coherence across time as various self-states become active is reflected in the concept of integration, the central topic of Chapter 9. "Integration" refers to the way the mind establishes a functional flow in the states of mind across time. An important means of assessing integration is in the coherence of the structure of autobiographical narratives. Narrative coherence is reflected in both the way a life story is told and the manner in which life activities are lived. These linguistic and behavioral outputs are generated from a proposed central integrative process. Developing the capacity to integrate mental coherence is profoundly influenced by experience. In this way, attachment histories revealed in adult attachment narratives reflect the capacity of the individual to integrate a coherent sense of self.     By organizing the self across past, present, and future, the integrating mind creates a sense of coherence and continuity. In various forms of mental dysfunction, integration may be impaired, leading to a sense of paralysis or chaos. The ways in which human relationships foster resilience and emotional well-being by facilitating an integrative capacity are explored as part of the developmental framework of mind, brain, and interpersonal experience. APPROACHING NEUROBIOLOGY What are the mechanisms by which human relationships shape brain structure and function? How is it possible for interpersonal experience--the interactions between two people--to affect something so inherently different as the activity of neurons? Though this book is organized by a focus on the mental processes described above, exploring insights from neuroscience will greatly enhance our ability to address these basic questions. For this reason, this introductory chapter offers a brief overview of some relevant aspects of neurobiology--the study of the way neurons work and how the brain functions.     (A brief note for those new to thinking about the brain: The aim of the book is to help you to understand the developing mind by providing an integration of mental processes [such as memory and emotion] with both neurobiology [such as neural activity in specific circuits] and interpersonal relationships [such as patterns of communication]. This integration is indeed the challenge of the book, both in the writing and in the reading. My concern is that those who are new to neurobiology--like many of my students in the past--may initially feel too overwhelmed at the unfamiliar ideas and vocabulary to continue. Numerous teaching experiences, however, have demonstrated that the outcome is worth the effort. There are many readily accessible concepts and much useful information just below the surface of these sometimes new names and ideas. A shared understanding of neurobiology from the beginning will help you in making sense of the intricate and exciting findings about interpersonal relationships and the developing mind. I have tried to include enough of a background as the chapters evolve that each domain can be understood by those who may be totally unfamiliar with a given area. New concepts and vocabulary are inevitable, but I have tried to incorporate information throughout the book in a "user-friendly" manner, summarizing the significance of certain findings and including reminders of certain trends as they recur in the book. For those who are charting new waters, I welcome you to the exciting world of interdisciplinary study!)     What follows is a brief overview of some relevant highlights from neurobiology. This information may be useful as a resource later in the book and is offered here as an introductory frame of reference. The Organization of the Brain The brain is a complex system of interconnected parts. The "lower structures" include those circuits of the brainstem deep within the skull that mediate basic elements of energy flow, such as states of arousal and alertness and the physiological state of the body (temperature, respiration, heart rate). At the top of the brainstem is the thalamus, an area that serves as a gateway for incoming sensory information and has extensive connections to other regions of the brain, including the neocortex, just above it. As we shall see, one theory considers the activity of the thalamocortical circuit to be a central process for the mediation of conscious experience. The "higher structures," such as the neocortex at the top of the brain, mediate "more complex" information-processing functions such as perception, thinking, and reasoning. These areas are considered to be the most evolutionarily "advanced" in humans and mediate the complex perceptual and abstract representations that constitute our associational thought processes. The centrally located "limbic system"--including the regions called the orbitofrontal cortex, anterior cingulate, and amygdala--plays a central role in coordinating the activity of higher and lower brain structures. The limbic regions are thought to mediate emotion, motivation, and goal-directed behavior. Limbic structures permit the integration of a wide range of basic mental processes, such as the appraisal of meaning, the processing of social experience (called "social cognition"), and the regulation of emotion. This region also houses the medial temporal lobe (toward the middle, just to the sides of the temples), including the hippocampus, which is thought to play a central role in consciously accessible forms of memory. The brain as a whole functions as an interconnected and integrating system of subsystems. Although each element contributes to the functioning of the whole, regions such as the limbic system, with extensive input and output pathways linking widely distributed areas in the brain, may be primarily responsible for integrating brain activity. When we look to understand how the mind develops, we need to examine how the brain comes to regulate its own processes. Such self-regulation appears to be carried out in large part by these limbic regions.     The limbic and lower regions of the brain also house the hypothalamus and the pituitary, which are responsible for physiological homeostasis, or bodily equilibrium, established by way of neuroendocrine activity (neuronal firing and hormonal release). Stress is often responded to by the "hypothalamic-pituitary-adrenocortical (HPA) axis," and this system can be adversely affected by trauma. This neuroendocrine axis, along with the autonomic nervous system (regulating such things as heart rate and respiration) and the neuroimmune system (regulating the body's immunological defense system) are ways in which the function of the brain and body are intricately intertwined.     To gain a visual grasp of some of this brain structure, it may be helpful to use a readily available, three-dimensional model that will enable you to have neuroanatomy in the palm of your hand, so to speak. If you make a fist with your thumb bent toward the center of your palm and your fingers curled around it and resting on the lower part of your hand, you'll have a model of the brain: Your lower arm represents the location of the spinal cord inside the backbone and your wrist is at the base of the skull; the various parts of your hand represent the three major regions we've discussed above--lower, limbic, and neocortical areas. Looking directly at your fist from the palmar side, the orbits of the eyes would emerge around the areas of the fingernails of your third and fourth fingers. The ears would extend from either side of your fist. Your fingers represent the neocortex: Facing you are its frontal lobes; at the top are the neocortical areas that mediate motor control and somatosensory representations; to the sides and back of your hand are the posterior parts that mediate perceptual processing. The lower parts of the brain are represented by the midline portion of your lower palm. Just below your knuckles, deep inside your fist where the end of your thumb rests, is the limbic system. Most of the brain is split into the left and right hemispheres, which are connected with bands of tissue called the corpus callosum and the anterior commissures, thought to serve as direct sources of information transfer between the two sides of the brain. The cerebellum, which would be located at the back of your hand near its connection to your wrist, may also indirectly transfer information across the division that separates the two halves of the brain. The cerebellum itself may carry out a number of informational and integrating processes.     The areas of your fist jutting out from the front of your palm are the frontal lobes. The very front of this anterior region is called the prefrontal cortex, an area we will be exploring throughout the book. We will examine two important aspects of this frontal neocortical region: the ventral medial (also known as the orbitofrontal cortex, the term we shall use in this book) and the lateral prefrontal cortex. The lateral prefrontal cortex rests to the sides (thus "lateral") and is represented by your index finger on one side and your fifth finger on the other. The lateral prefrontal cortex is thought to play a major role in working memory and the focusing of conscious attention. On your fist model, the orbitofrontal area lies, as you may have guessed, just behind and above the orbits of the eyes, especially where your last knuckles bend and the tips of your fingers push inward toward your palm. Notice that in this position the orbitofrontal region is adjacent to a number of areas from which it receives and to which it sends pathways carrying information: the deeper structures of the brain that process sensory and bodily data, the limbic system itself, and the neocortex just above it. In this manner, the orbitofrontal region can be seen, in fact, as the uppermost part of the limbic system as well as a part of the frontal lobes of the neocortex. Some call this area a part of the "paralimbic" cortex. This three-dimensional model thus gives you a direct experiential/ visual example of neural interconnections and the relevance of anatomy for coordinated function.     The brain is highly interconnected, and controversy exists in academic circles about how distinct these regions actually are in anatomy and function. The notion of a limbic "system," for example, has been challenged, in that defining its limits (where it starts and where it ends) has been scientifically difficult. Nevertheless, the limbic regions appear to utilize specific neurotransmitters, to have highly interconnected circuitry, to carry out complementary functions, and to have similarities in their evolutionary history. For example, the orbitofrontal cortex, sitting at the top of the limbic system and anatomically connected to a wide array of areas in the neocortex and the deeper structures of the brain, carries out a vital role in the coordination of the activity from all three regions. As we shall see, recent studies from neuroscience suggest that this orbitofrontal region may play a major role in many of the integrating processes we will be examining, such as memory, emotion, and attachment.     The brain has an estimated one hundred billion neurons, which are collectively over two million miles long. Each neuron has an average of ten thousand connections that directly link itself to other neurons. Thus there are thought to be about one million billion of these connections, making it "the most complex structure, natural or artificial, on earth." A neuron sends an electrical impulse down its long axons; this releases a neurotransmitter at the space at the end, called a "synapse," which then excites or inhibits the downstream neuron. A synapse is the connection that functionally links neurons to one another. Because of the spider-web-like interconnections, activation of one neuron can influence an average of ten thousand neurons at the receiving ends! The number of possible "on-off" patterns of neuronal firing is immense, estimated as a staggering ten times ten one million times (ten to the millionth power). The brain is obviously capable of an imponderably huge variety of activity; the fact that it is often organized and functional is quite an accomplishment! Brain Development The activation of neural pathways directly influences the way connections are made within the brain. Though experience shapes the activity of the brain and the strength of neuronal connections throughout life, experience early in life may be especially crucial in organizing the way the basic structures of the brain develop. For example, traumatic experiences at the beginning of life may have more profound effects on the "deeper" structures of the brain, which are responsible for basic regulatory capacities and enable the mind to respond later to stress. Thus we see that abused children have elevated baseline and reactive stress hormone levels. More common, everyday experiences also shape brain structure. The brain's development is an "experience-dependent" process, in which experience activates certain pathways in the brain, strengthening existing connections and creating new ones. Lack of experience can lead to cell death in a process called "pruning." This is sometimes called a "use-it-or-lose-it" principle of brain development. An infant is born with a genetically programmed excess in neurons, and the postnatal establishment of synaptic connections is determined by both genes and experience. Genes contain the information for the general organization of the brain's structure, but experience determines which genes become expressed, how, and when. The expression of genes leads to the production of proteins that enable neuronal growth and the formation of new synapses. Experience--the activation of specific neural pathways--therefore directly shapes gene expression and leads to the maintenance, creation, and strengthening of the connections that form the neural substrate of the mind. Early in life, interpersonal relationships are a primary source of the experience that shapes how genes express themselves within the brain.     At birth, the infant's brain is the most undifferentiated organ in the body. Genes and early experience shape the way neurons connect to one another and thus form the specialized circuits that give rise to mental processes. In this way, experiences early in life have a tremendously important impact on the developing mind. The differentiation of circuits within the brain involves a number of processes including (1) the growth of axons into local and widely distributed regions; (2) the establishment of new and more extensive synaptic connections between neurons; (3) the growth of myelin along the lengths of neurons, which increases the speed of nerve conduction and thus "functionally" enhances the linkage among synaptically connected nerve cells; (4) the modification of receptor density and sensitivity at the postsynaptic "receiving" cell making connections more efficient; and (5) the balance of all of these factors with the dying away or pruning of neurons and synapses resulting from disuse or toxic conditions such as chronic stress. In experimental animals, enriched environments have been shown to lead to increased density of synaptic connections and especially to an increased number of neurons and actual volume of the hippocampus, a region important for learning and memory. Experiences lead to an increased activity of neurons, which enhances the creation of new synaptic connections. This experience-dependent brain growth and differentiation is thus referred to as an "activity-dependent" process.     Interpersonal experiences continue to influence how our minds function throughout life, but the major structures--especially those that are responsible for self-regulation--appear to be formed in the early years. It is for this reason that we will look closely at the early years of life to understand the ways in which the mind develops and comes to regulate its own processes. An open question in neurobiology is how "plastic," or open to further development, the brain remains throughout the lifespan. We can look toward the lessons from studies of early interpersonal experience to try to understand the ways in which relationships may continue to foster the development of the mind throughout life. Information Processing and Neurobiology From an information-processing perspective, brain anatomy and neural circuit functioning can be understood as follows. Signals from the deep structures representing physiological data from the body are received and processed by the centrally located limbic structures. More elaborately processed data from the activities of the limbic system itself are integrated by limbic regions, including the orbitofrontal cortex and anterior cingulate. These areas send emotional and somatosensory input to the neocortex, which also processes perceptual representations from the sensory cortices, conceptual from the associational cortices, and linguistic representations from the language-processing centers. The information-processing task of integrating regions such as the associational cortices and orbitofrontal cortex is to take in the different neural "codes," coordinate the information contained within these signals, and "translate" them into transformed neural activity, which then is sent as output to the various regions. Such neural translation of the various forms of representations allows for information to be both processed and then communicated in different codes to the relevant regions. This translation process allows for a type of neural integration of complex information within the mind.     An analogy is this: We can transmit an electronic mail message with a file containing the twenty-six letters of the alphabet, spacing, and a handful of punctuation marks. With electrical flow through wires in a pattern of impulses, we can send a detailed written note. Through the same wires, we can send an entire photograph or even a video. Though the message contains different information (note, photo, video), the fundamental form in which the data is transmitted is identical--electrical impulses flowing as patterns of energy through a wire. The information contained within the different messages varies in its patterns and its complexity. Without the proper receiving device to translate these electrical impulses into words, pictures, or video, the complex representation has no meaning.     The same is true with the brain. Neural activity is the fundamental form in which information is transmitted. The sending area is capable of transmitting a certain kind of information as neural codes. The receiving circuits or systems must be capable of processing such signals for them to have any meaning. The brain is genetically programmed to be able to differentiate its regions, which carry different forms of information. These forms vary in pattern and complexity from the most "simple" signals of the deeper structures (such as heart rate) to the more complex ones of the neocortex (such as ideas about freedom or about the mind itself). Experience not only provides the input that serves to activate (give the information to) these regions; it is necessary for the proper development of the brain itself. Experience-dependent maturation is a part of even the basic sensory systems of our brains. The brain must "use it or lose it" in many cases of brain specialization. For example, studies in animals reveal that the lack of exposure to certain types of visual information, such as vertical lines, during a critical period early in life leads to loss of the capacity for perceiving such lines later in life. Specific forms of experience are necessary for the normal development of information-processing circuits in the visual cortex. The same process may occur for other systems in the brain, such as the attachment system. Children who have had no experience with an attachment figure (not merely suboptimal attachment, but a lack of attachment) for the first several years of life may suffer a significant loss of the capacity to establish intimate interpersonal relationships later on.     In this way, we can reexamine one of our initial questions: How does experience shape the mind? A general principle can be proposed here: Experiences can shape not only what information enters the mind, but the way in which the mind develops the ability to process that information . How this occurs can be seen as the modification of the actual circuits of the brain responsible for processing that particular type of information. Experience creates representations, as well as stimulating the capacity for specific forms of information processing. The Brain as a System At the most basic level, the brain can be considered as a living system that is open and dynamic. It is an integrated collection of component subsystems that interact together in a patterned and changing way to create an irreducible quality of the system as a whole. A living system must be open to the influences of the environment in order to survive, and the brain is no exception. The system of the brain becomes functionally linked to other systems, especially to other brains. The brain is also dynamic, meaning that it is forever in a state of change. An open, dynamic system is one that is in continual emergence with a changing environment and the changing state of its own activity.     Furthermore, the brain is a complex system, meaning that there are multiple layers of component parts capable of chaotic behavior. These parts can be conceptualized at various levels of analysis, and include the single neuron and its sending and receiving functions; neuronal groups; circuits; systems; regions; hemispheres; and the whole brain. The basic components, the neurons, are the simplest. As we move up the levels of components, the units become more and more elaborate. Some authors use the terms "lower-order" to refer to the basic level of organizational unit and "higher-order" to refer to the more intricate level of organization. For the most part, each subsystem can be considered to have both lower and higher orders of systems with which it relates. For example, the activity of the visual cortex is made up of the lower-level input from the eyes, but itself contributes to the higher-level processing of the entire perceptual system.     From the point of view of the brain as an open system, each region of the brain may take in unique input from outside of itself. The deeper structures of the brain receive sensory input from the body and from the external world; the limbic system receives input from the deeper structures and from the neocortex; and the neocortex receives data from the limbic system itself. Neuroanatomic studies reveal that the neocortical regions are also intricately interwoven with the "lower" levels of the system, and thus our "higher thinking" is actually directly dependent upon activity of the entire brain. The regions coordinating the state of activation of the subcomponents of the brain, however, are not in the "most evolved," higher-level neocortex. For this reason, the limbic system is more effective in the regulation of the body and emotions than the "higher" neocortex. This finding also demonstrates how emotions, generated and regulated by the activity of the limbic system, are integral parts of our neocortically derived "rational thoughts" as well as the overall functioning of our minds.     These issues also suggest that specific circuits within the brain may function as somewhat distinct "subsystems" that create their own predominant states of processing. For example, the left and right sides of the brain have distinct circuits that become predominant early in life, even in the embryo. Each of these pathways has its dominant neurotransmitters and involves distinct evaluative components that serve to direct each hemisphere to process information in distinct manners. How each hemisphere is activated will directly shape our subjective sensations and the ways in which we communicate with others. (Continues...) Copyright © 1999 Daniel J. Siegel. All rights reserved.