30-Second Brain 30-Second Brain E-Book

• Herausgeber: Icon Books
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 158

Veröffentlichungsjahr: 2014

Beschreibung

Are we all at the mercy of our brain chemistry? Do you think that the amygdala and the hippocampus are fantastical sea monsters? What can an MRI scan tell us? Could you explain to dinner-party guests why we don't giggle when we tickle ourselves? 30-Second Brain is here to fill your mind with the science of exactly what's happening inside your head. Using no more than two pages, 300 words and an illustration, this is the quickest way to understand the wiring and function of the most complex and intricate mechanism in the human body. Discover how the networks of 90 billion nerve cells work together to produce perception, action, cognition and emotion. Explore how your brain defines your personality, and what it gets up to while you are asleep. Illustrated with mind-bending graphics and supported by biographies of pioneers in the field of neuroscience, it's the book to get your grey matter thinking about your grey matter.

Leseprobe

30-SECOND

BRAIN

The 50 most mind-blowing ideas in neuroscience, each explained in half a minute

Editor

Anil Seth

Foreword by

Chris Frith

Contributors

Tristan Bekinschtein

Daniel Bor

Christian Jarrett

Ryota Kanai

Michael O’Shea

Anil Seth

Jamie Ward

Are we all at the mercy of our brain chemistry?

Do you think that the amygdala and the hippocampus are fantastical sea monsters?

What can an MRI scan tell us?

Could you explain to dinner-party guests why we don’t giggle when we tickle ourselves?

30 Second Brain is the quickest way to understand what’s happening inside your head, challenging experts in the field to explain the 50 most mind-blowing theories in neuroscience. Each entry is summarized in just 30 seconds – using nothing more than two pages, 300 words and a single picture. Discover how the networks of 90 billion nerve cells work together to produce perception, action, cognition and emotion. Explore how your brain defines your personality, and what it gets up to while you are asleep. Illustrated with mind-bending graphics and supported by biographies of pioneers in the field of neuroscience, it’s the book to get your grey matter thinking about your grey matter.

CONTENTS

Foreword

Introduction

Building the Brain

GLOSSARY

Neurons & Glial Cells

Neurotransmitters & Receptors

Neurogenetics

Profile: Santiago Ramón y Cajal

The Basic Architecture of the Brain

The Cerebellum

The Developing Brain

The Evolving Brain

Brain Theories

GLOSSARY

The Localization of Function

Hebbian Learning

Neural Networks

The Neural Code

Profile: Donald Hebb

The Oscillating Brain

Neural Darwinism

The Bayesian Brain

Mapping the Brain

GLOSSARY

Neuropsychology

Brain Imaging

The Human Connectome

Optogenetics

Profile: Wilder Penfield

Resting State

Left Brain vs Right Brain

Brain Stimulation

Consciousness

GLOSSARY

The Hard Problem

Sleeping & Dreaming

Profile: Francis Crick

Neural Correlates of Consciousness

Embodied Consciousness

Consciousness & Integration

Volition, Intention & ‘Free Will’

The Anaesthetized Brain

Coma & the Vegetative State

Perception & Action

GLOSSARY

We See Colours

Blindsight

Synaesthesia

Sensory Substitution

Missing the Obvious

How We Pick Up a Cup of Coffee

Profile: Oliver Sacks

Alien Hand Syndrome

Cognition & Emotion

GLOSSARY

The Remembering Brain

The Emotional Brain

The Imagining Brain

Profile: Paul Broca

The Linguistic Brain

Metacognition

Decision Making

Mirror Neurons

The Changing Brain

GLOSSARY

Neurogenesis & Neuroplasticity

Training the Brain

The Brain’s Personality

The Ageing Brain

The Parkinsonian Brain

Profile: Roger Sperry

The Schizophrenic Brain

The Meditating Brain

APPENDICES

Resources

Notes on Contributors

Acknowledgements

FOREWORD

by Chris Frith

The human brain is the most complex entity we know of. It contains at least 90 billion neurons (nerve cells). Each of these is a complex information-processing device in its own right and interacts with about 1,000 other neurons. Understanding this degree of complexity is a daunting task.

Our understanding of the human brain is still in its infancy. The identification of the neuron as the basic building block of the brain occurred only 100 years ago. At first, progress depended on the study of damaged brains. It is only in the last 25 years that it has become possible to see brain structure and function in healthy volunteers. The remarkably detailed images that emerge from brain scanners, with their brightly coloured blobs, have had a dramatic impact. Human brains have become the image of choice for the media, attached to articles about ‘What our brains can teach us’ or ‘Contours of the mind’.

Brain research is beginning to attract big money. The Brain Activity Map project is expected to receive $3 billion from the US Government over the next ten years. The hope is that investigating the human brain in exquisite detail will have a similar pay-off to that achieved by the human genome project and will lead to progress in understanding mental disorders, such as autism and schizophrenia.

One of the most exciting features of research on the human brain is that we confront deep philosophical questions. Minds depend on brains. Without brains we could not think, or feel, or imagine. But we still feel uncomfortable with this identity. Am I simply the product of electrical activity in my brain? How can subjective experience emerge from brain activity?

Our theories about how brains work remain very primitive. Some people think that an insoluble conundrum arises because the human brain is trying to understand itself. Surely something complex can only be understood by something even more complex? I believe that this problem is more apparent than real. Here’s why. One of the glories of the human brain is that it enables us to share our thoughts. Our understanding is built on the thinking of our predecessors as well as our contemporaries and far transcends the abilities of any single brain. We pay too little attention to these effects of culture and collaboration.

Sophisticated network

The brain is fired up by a network of 90 billion neurons. Neuroscientists are only just beginning to discover how their activity relates to what happens in our minds.

Consider another highly social animal, the bee. The brain of a bee weighs 1 milligram and contains a mere million neurons. Yet this tiny brain enables bees to learn about the world and communicate using their waggle dance. Even more impressive is what bees can achieve through collaboration. From the reports of scouts, a swarm of bees can make a group decisions about the best site for a new nest.

Recent studies suggest that the way the bees interact to make decisions closely resembles the way neurons in the human brain interact to make decisions. This comparison gives us a feel for the dramatically enhanced abilities of the human brain compared with the bee brain. But it also instils in me a sense of wonder about what humans can achieve as a group.

A group of bees working together can achieve abilities resembling those of a single human brain. Imagine an entity containing the power of multiple, interacting human brains. We create such a system whenever we interact. And the best example of the power of such a system comes from the practice of science. It is through the practice of science that we will be able to unravel the mysteries of the brain. This book shows how exciting this journey will be.

INTRODUCTION

Anil Seth

Understanding how the brain works is one of our greatest scientific quests. The challenge is quite different from other frontiers in science. Unlike the bizarre world of the very small in which quantum-mechanical particles can exist and not exist at the same time, or the mind-boggling expanses of time and space conjured up in astronomy, the human brain is in one sense an everyday object; it is about the size and shape of a cauliflower, weighs about 1.36 kg (3 lb) and has a texture like tofu. It is the complexity of the brain that makes it so remarkable and difficult to fathom. There are so many connections in the average adult human brain that if you counted one each second it would take you more than 3 million years to finish.

Faced with such a daunting prospect it might seem as well to give up and do some gardening instead. But the brain cannot be ignored. As we live longer, more and more of us are experiencing – or will experience – neurodegenerative conditions, such as Alzheimer’s disease. The incidence of psychiatric illnesses, such as depression and schizophrenia, is also on the rise. Better treatments for these conditions depend on a better understanding of the brain’s intricate networks.

More fundamentally, the brain draws us in because it defines who we are. It is much more than just a machine to think with. Hippocrates, the father of Western medicine, recognized this long ago: ‘Men ought to know that from nothing else but the brain come joys, delights, laughter and jests, and sorrows, griefs, despondency and lamentations.’ More recently Francis Crick – one of the major biologists of our time (see the biography) – echoed the same idea: ‘You, your joys and your sorrows, your memories and your ambitions, your sense of personal identity and free will, are in fact no more than the behaviour of a vast assembly of nerve cells and their associated molecules.’ And, perhaps less controversially, but just as important, the brain is also responsible for the way we perceive the world and how we behave within it. So to understand the brain is to understand our own selves and our place in society and in nature.

More than a machine

The brain is a complex and intricate information-processing mechanism – not just for cold, hard facts but for how we move, feel, laugh and cry. Neuroscientists are constantly gaining new insights into the inner workings of the brain.

But how to begin? From humble beginnings, neuroscience is now a vast enterprise involving scientists from many different disciplines and almost every country in the world. The annual meeting of the Society for Neuroscience attracts more than 20,000 (and sometimes more than 30,000) brain scientists. No single person – however capacious their brain – could possibly keep track of such an enormous and fast-moving field. Fortunately, as in any area of science, underlying all this complexity are some key ideas to help us get by. Here’s where this book can help.

How the book works

Within the following pages, leading neuroscientists and science writers will take you on a tour of 50 of the most exciting ideas in modern brain science, using simple plain English. To start with, in Building the Brain we will learn about the basic components and design of the brain, and trace its history from birth (and before), and through evolution. Brain Theories will introduce some of the most promising ideas about how the brain’s many billions of nerve cells (neurons) work together. Mapping the Brain will show how new technologies are enabling us to chart the brain’s intricate structure and activity patterns. Then, in Consciousness, we tackle the still mysterious relationship between the brain and conscious experience – how does the buzzing of neurons transform into the subjective experience of being you, here, now, reading these words? In the following chapters, Perception & Action and Cognition & Emotion, we will explore how the brain enables these important functions, both with and without consciousness. Finally, in the last chapter – The Changing Brain – we will explore some recent ideas about how the brain changes its structure and function throughout life in both health and in disease.

Approach the book however you like. Read it in order, or dip in and out. Each of the 50 ideas is condensed into a concise, accessible, and engaging ‘30-second neuroscience’. To get the main message across, there is also a ‘3-second brainwave’, and a ‘3-minute brainstorm’ provides some extra food for thought on each topic. There are helpful glossaries summarizing the most important terms used in each chapter, as well as biographies of key scientists who helped make neuroscience what it is today. Above all, I hope to convey that the science of the brain is just getting into its stride. These are exciting times and it’s time to put the old grey matter through its paces.

Mind-blowing

What’s happening inside your head? Imaging technology, genetics, chemistry and computing reveal our brains in increasingly more minute and technicolor detail.

BUILDING THE BRAIN

BUILDING THE BRAIN

GLOSSARY

axon A long, thin fibre extending from the cell body (soma) of a neuron, conveying its output in the form of a spike (nerve impulse or action potential) and enabling communication with other neurons. Each neuron will have at most one axon. Axons typically split into many separate branches before connecting with the dendrites of other neurons.

brain stem A small stalk-like area at the bottom of the brain, lying in between the spinal cord and the rest of the brain. The brain stem controls many vital basic bodily functions, such as breathing, swallowing and blood pressure regulation. Because so many neural pathways pass through the brain stem, damage to this area can have profound effects.

cerebral cortex The deeply folded outer layers of the brain, which take up about two-thirds of its entire volume and are divided into left and right hemispheres that house the majority of the ‘grey matter’ (so called because of the lack of myelination that makes other parts of the brain seem white). The cerebral cortex is separated into lobes, each having different functions, including perception, thought, language, action and other ‘higher’ cognitive processes, such as decision making.

dendrites The short input fibres of a neuron that are organized into complicated tree-like patterns. Each neuron has many dendrites that make contact with axons from other neurons via synapses. Dendrites convey the incoming signals to the cell body (soma) of a neuron, which will then produce an output of its own.

frontal lobes One of the four main divisions of the cerebral cortex and the most highly developed in humans compared with other animals. The frontal lobes (one for each hemisphere) house areas associated with decision making, planning, memory, voluntary action and personality.

hippocampus A sea horse-shaped area found deep within the temporal lobes. The hippocampus is associated with the formation and consolidation of memories and also supports spatial navigation. Damage to this area can lead to severe amnesia, especially for episodic (autobiographical) memories.

myelination A process by which a neuron’s axons are coated with myelin, which both insulates the axon from other nearby axons and dramatically increases the speed of nerve impulses (spikes) travelling along it. Myelination, which relies on glial cells, is essential for efficient transmission of information in the brain.

occipital lobes Another of the four main divisions of the cerebral cortex, the occipital lobes are at the back of the brain and house regions mainly involved in vision. Damage to the occipital lobes can result in blindness or more selective deficits.

olfactory system One of the most evolutionarily ancient parts of the brain. The olfactory system underpins the sense of smell and is less well-developed in humans than in many other animals. Signals from olfactory sensory neurons in the nose are conveyed to the olfactory bulb deep inside the brain. Olfaction and taste are distinct from the other senses by responding to chemical stimulation.

parietal lobes The third major division of the cerebral cortex. The parietal lobes lie above the occipital lobes and behind the frontal lobes and are deeply involved in integrating information from the different senses. The parietal cortex is essential for organizing our experience of space and position and it is heavily involved in attentional processes.

Purkinje cells Found exclusively in the cerebellum, these neurons are among the largest in the brain and have elaborately branching dendritic structures. Purkinje cells provide long-range inhibitory control over output parts of the cerebellum, enabling fine motor co-ordination and error correction.

synapses The junctions between neurons, linking the axon of one to a dendrite of another. Synapses ensure that neurons are physically separate from each other so that the brain is not one continuous mesh. Communication across synapses can happen either chemically via neurotransmitters or electrically.

temporal lobes The last of the four main divisions of the cerebral cortex. These lobes are found low to the side of each hemisphere and are heavily involved in object recognition, memory formation and storage and language. The hippocampus is in the medial part of these lobes (the medial temporal lobe).

thalamus These are bundles (nuclei) of neurons that sit on top of the brain stem and are about the size and shape of a walnut. The thalamic nuclei are heavily interconnected with specific areas of the cerebral cortex and are thought to act as sensory relay areas, connecting sensory receptors (apart from olfaction) with the cortex.

NEURONS & GLIAL CELLS

the 30-second neuroscience

Your neurons (your marbles, if you prefer) are the information processing cells of your brain. You have between 90 and 100 billion of them, yet not one of them has any idea who you are. But somehow, by chattering among themselves across networks of billions of interconnections, neurons conjure up your self-awareness. Neurons receive messages from other neurons on their cell body and its short extensions – called dendrites – at specialized structures called synapses. Messages are sent to other neurons via long, slender fibres – called axons – in coded patterns of electrical spikes (nerve impulses). Each impulse is about 0.1 volt and lasts one- to two-thousandths of a second, hurtling along axons at up to 480 kph (300 mph). Arriving at a synapse, impulses trigger the release of signalling chemicals called neurotransmitters. These alter the pattern of spikes generated by the receiving neuron. And that is basically how the brain works. Well, not quite. Neurons work properly only if bathed in the right blend of chemicals. Glial cells, which outnumber neurons 50:1, maintain this condition. They help neurons wire together in the developing brain, nurture them in the adult brain, insulate axons, mop up dead cells, recycle used neurotransmitters and protect the brain from infection. They are the unsung heroes of the brain’s story.

3-SECOND BRAINWAVE

There are 4 km (2½ miles) of neuronal network interconnections packed into every cubic millimetre of grey matter.

3-MINUTE BRAINSTORM

Could you think yourself thin? The brain is just two per cent of your body weight but consumes twenty per cent of your daily energy needs. Exercising the brain is energetically expensive. In spite of this, as humans evolved, the most thoughtful part of the cerebral cortex rapidly tripled in size beginning about two million years ago. Most of the additional cost of evolving our uniquely human cognitive abilities is consumed by a single enzyme that recharges the batteries that power electrical nerve impulses.

RELATED BRAINPOWER

NEUROTRANSMITTERS & RECEPTORS

NEURAL NETWORKS

3-SECOND BIOGRAPHIES

SANTIAGO RAMÓN Y CAJAL

1852–1934

Anatomist who defined the cellular components of mental activity

WALTHER NERNST

1864–1941

His theoretical work explained how voltages are generated by cells

BERNARD KATZ

1911–2003

Proposed the quantum/vesicular hypothesis of neurotransmitter release

30-SECOND TEXT

Michael O’Shea

For every networking executive neuron, there are 50 low-status but essential glial cells maintaining the neural environment.

NEUROTRANSMITTERS & RECEPTORS

the 30-second neuroscience

Neurotransmitters convey signals