The Mind-Brain Relationship

Regina Pally

• Publisher: Routledge
• Year: 2018
• eBook ISBN: 9780429921469
• Topic: Psychology
• Subtopic: History & Theory in Psychology
• Index: Psychology

This book describes how neural circuitry develops epigenetically, in a manner that directly reflects early environmental influences. It provides a systematic and comprehensive overview of the state of the art in the field, and discusses the structure and function of memory.

1
How Brain Development is Shaped by Genetic and Environmental Factors

We have entered an era of extraordinary discovery about the human brain. Old notions of dichotomy between mind versus brain, nature versus nurture, have been supplanted by a rich web of synergistic relations between mind and brain, nature and nurture. Specifically, according to modern neuroscience, this means that all mental phenomena are assumed to be the result of biological activity of neuronal circuits in the brain. The development of these circuits relies in part on genetic programmes, but is also heavily dependent on the individual’s experiences within the environment.

Recognition of the remarkable degree to which brain development is experience-dependent is a striking example of how neuroscience can be integrated with psychoanalysis. These ideas can be considered to lend support to analytic assumptions that early developmental experiences shape subsequent psychological functioning. The overall aim of this book is to integrate the two fields by providing a schematic overview of neuroscience topics that are relevant to the theory and practice of psychoanalysis. In this way the reader will not only know facts about brain functions, but be able to think conceptually about how these functions operate with one another and how they may inform us about our analytic work.

For some, this way of considering The Mind’ may be rather foreign and difficult to accept. However, as Olds and Cooper in their recent editorial on the value of neuroscience for psychoanalysis recommend: We should at least understand what we are being offered, before deciding whether or not’ it is profitable to us (1997, p. 221). The idea that mental life is derived from biological events in neuronal circuits is the reigning doctrine of neuroscience, and therefore must be taken as a starting point for understanding the empirical research based on it. For those who criticise these attempts at integration as ‘reductionistic, I want to clarify that the emphasis here is that mental phenomena are derived from biological activity. There is no intention to equate the mental with the biological.

I have selected topics that are most readily integrated with psychoanalysis. In this first chapter I address the experience-dependent nature of brain development. The three subsequent chapters cover perception, memory and emotion, and the two following chapters address aspects of bilaterality and consciousness. The concepts build on one another with each subsequent chapter. The data presented throughout is the result of a compilation of animal research and human research, including in vivo PET scans and MRIs and computer models of brain function. Before proceeding to how brain development is shaped by environmental as well as genetic influences, some preliminary comments are necessary regarding the unique cellular architecture and the evolutionary history of the human brain.

CELLULAR ARCHITECTURE OF THE BRAIN

The brain consists of approximately 10 billion neurons (10⁹) all activated at the same time (Edelman, 1992; Edelman & Tononi, 2000). Each individual neuron, with its axon and branching dendrites, makes a synaptic connection with approximately 60,000 to 100,000 other neurons. The total number of synaptic connections is in the range of 10²⁷. The number of possible combinations of synaptic connections is in the range of 10^million. This is more than the number of positively charged particles in the known universe! The almost infinite number of potential neuronal configurations provides for the brain’s vast information processing capacity.

EVOLUTION OF THE HUMAN BRAIN

The architecture and organisation of the brain is the product of its evolutionary history, which indicates that the human brain has evolved and expanded, while still retaining features of three basic ‘evolutionary ancestors’, reptiles, lower mammals and primates (MacLean, 1990). As a result of natural selection, ‘newer brain structures, which could ‘perform’ more adaptive functions, were added on to, and integrated with, more primitive structures. The most primitive part, the brainstem, is responsible for vital functions of physiological survival, such as the sleep/wake cycle, heart rate, respiration and body temperature. In addition to the brainstem, the human brain contains structures that are remnants of ‘ancestral’ brains. Derived from reptilian ancestors is the striatum, also called the basal ganglia. It is responsible for behavioural motor routines that are unique to the particular species, such as territorial displays. Humans have few of the innate behavioural routines found in reptiles and lower animals. However, in humans, once a particular behaviour is repeated many times, such as riding a bicycle or playing a Mozart concerto, the motor patterns are stored in the basal ganglia and can be activated as automatic motor routines. Derived from lower mammals is the palaeomammalian brain, or limbic system. It is associated with emotion and memory, as well as with uniquely mammalian behaviours such as nursing, parental care, play and the infant distress cry.

The most highly evolved part of the brain is the cortex, or neomammalian brain. The part of the cortex that reaches the greatest degree of development in humans is called the prefrontal cortex. It is the executive centre of the brain, responsible for planning for the future, directed attention to a task, delay of gratification, affect regulation and voluntary control of movement (Damasio, 1994; Fuster, 1996). The ‘higher, more advanced prefrontal cortex modulates the emotion, behaviour and body physiology processed by the ‘lower’, more primitive subcortical regions.

There is a tendency to speak about the brain as if a particular function is localised in a particular brain region. However, the brain operates as a dynamic integrated whole (Edelman, 1989). Even a simple perception, such as seeing a cat, involves circuits that traverse the brainstem, limbic system and prefrontal cortex.

GENETIC INFLUENCES ON BRAIN DEVELOPMENT

One half of the entire genome is dedicated to producing the brain, an organ that constitutes only 2 per cent of our body weight. For the nine months of gestation and for a few months after birth, brain growth and development is largely directed by the genetic code (Scheibel & Conrad, 1993). For example, the process by which cells migrate from the primitive neural tube tissue to their final destination in the foetal brain is under direct genetic influence. Another example is that after cells migrate, they develop temporary connections, which ‘hold the place’ for the more permanent connections that follow. Abnormalities of cell migration may contribute to the development of schizophrenia. One example, after birth, is the myelin sheath, which permits more rapid conduction of impulses along the axon (Kinney et al., 1988). Primary sensory areas myelinate in the first months of life. The prefrontal cortex, a region of higher cognitive skills, begins myelinating at about 3 months of age and continues into young adulthood!

ENVIRONMENTAL INFLUENCES ON BRAIN DEVELOPMENT

The brain is ‘born’ prematurely. Therefore much of its development occurs postnatally and for many years afterwards. Despite all the rich anatomical connections created under genetic control, the genome is not sufficient to encode all the details as to which connections ultimately become functionally active. To a startling degree, it is interactions with the environment that stimulate the more precise wiring of neural connections (Scheibel & Conrad, 1993). Illustrations of the experience-dependent nature of brain development exist at every level of brain functioning, from the rapid growth of the brain in early childhood to the subtler modifications that occur throughout the lifespan.

How neural circuits are wired

Neuroscientists believe that the functional unit of mental activity is not the single neuron but a circuit of interconnecting neurons all activated at the same time. Perception, memory, emotion, even thoughts and behaviours, are all the product of activated neural circuits. Interactions with the environment cause neurons to wire into circuits, which are sometimes called neural networks or neural assemblies, terms derived from computer models of brain activity. When the brain is exposed to a new event, external (a face, a word) or internal (emotion, physiological state), a unique pattern of neurons is activated. In order to preserve this configuration, connections must be forged between the neurons, creating a new circuit that acts as a symbol, a representation of something in the outside or Inside’ world. In other words, information from internal and external sources is represented in the brain by complex configurations of interconnected neurons (Edelman, 1989).

Recognition occurs when we encounter something that evokes a neural pattern similar to one already preserved, as demonstrated in primate brains and in computer-based neural network modelling (Edelman, 1992; Grossberg, 1999).¹ If a pattern of neurons lights up’ when you first see the Mona Lisa, the next time you see it, a similar pattern will light up, giving you the sense of recognition. (This process is often referred to as ‘pattern matching.) Because there is redundancy of brain circuits, it is even more accurate to say that a number of specific neural circuits underlie a particular brain function (Edelman, 1989). Redundancy is adaptive, because if one circuit becomes damaged, another can take its place. Not only is there more than one circuit per function, but individual neurons participate in many circuits, in the way that pixels in a television screen participate in a number of images.

The process by which most neuroscientists suppose connections between neurons are forged is called ‘Hebb’s rule’, which states that if two neurons tend to be electrically active at the same time they will automatically form a connection (Hebb, 1949). If they are already weakly connected, the synapses between them will become strengthened. With regard to brain development it is a matter of ‘use it or lose it’. We are born with an overabundance of neurons and dendrites (Diamond, 1988). In the neonatal period a pruning process begins. As a result of experience-dependent circuit development, the neural paths that are used remain, while those that are not used die off.

The role of re-entry circuits

All localised brain regions are richly connected to other brain regions by interconnecting neurons that form re-entry circuits (Edelman, 1989). These circuits, which also depend on experience-dependent ‘Hebbian’ strengthening, automatically feed information processed in localised brain regions back and forth to other localised regions. It is known that individual attributes of the environment are processed separately. There are relatively separate brain regions to process environmental features such as colour, contour, motion, sound. Other regions for processing the memory of these stimuli and other regions are specialised for coordinated motor responses to these stimuli. Through re-entry the brain co-ordinates the information from these separate stimulus processing regions. For example, information processed in the visual cortex, automatically influences processing in the auditory cortex and vice versa. Thus what you see will influence what you hear and what you hear influence what you see. Edelman emphasises that re-entry is an important component of the brain’s ability to accomplish complex cognitive tasks.

Sensitive periods for sensory cortex development

Although it has been most extensively studied within the visual system, it is considered a general principle that for normal perceptual capacity to emerge, the sensory cortex must receive very specific kinds of stimulation within a particular time frame, or ‘sensitive period’. In utero development provides only an approximate sketch of the wiring of the topographically arranged visual cortex. The more precise wiring requires stimulation from postnatal sensory experiences.

Animal experiments were conducted to illuminate the clinical observation that childhood cataracts, if not treated promptly, can lead to permanent blindness. These effects are limited to a sensitive period in childhood. Cataracts that develop later in life, but are surgically corrected, do not lead to blindness.

For binocular vision to develop in monkeys, the brain must receive stimulation from both eyes, within the first six months of life (Hubel & Wiesel, 1962). (In humans the sensitive period extends over the first several years). Normal binocular vision requires that cells in the 4c layer of area 17 of the visual cortex be segregated into clearly defined bands of columnar cells, a topographical arrangement that reflects the distinct axon terminal inputs from each eye. If one eye is sutured at birth, and unsutured at 6 months of age, there is permanent loss of useful vision in that eye. This is associated with failure of cells to segregate into distinct bands. While at birth, axon terminals from each eye project to this cortical area, as a result of sensory deprivation due to suturing the terminals from the deprived eye retract. Those from the normal stimulated eye grow overabundantly, moving into areas they would normally have relinquished to the now retracted terminals.

Sensitive periods for the prefrontal cortex

Even more relevant for psychoanalysts is the picture that is emerging regarding sensitive periods for emotional development. Using a combination of animal and human studies, Schore (1994) proposes a sensitive period of between approximately six months and one year for the development o...

Table of contents

• Cover
• Half Title
• Title
• Copyright
• CONTENTS
• Series Preface
• Foreword
• Introduction
• 1: How brain development is shaped by genetic and environmental factors
• 2: How the brain actively constructs perceptions
• 3: Memory: brain systems that link past, present and future
• 4: Emotional processing—the mind-body connection
• 5: Bilaterality: hemispheric specialisation and integration
• 6: Consciousness: a neuroscience perspective
• Index