Moheb Costandi - 50 Human Brain Ideas You Really Need to Know

ideas
you really need to know

the human brain

Moheb Costandi

First published in 2013

This ebook edition published in 2013 by

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Copyright 2013 Moheb Costandi

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eBook ISBN 978 1 78206 252 3
Print ISBN 978 1 78087 910 9

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All illustrations by Patrick Nugent except p.34 Natural History Museum, London/Science Photo Library

Contents

STRUCTURE AND FUNCTION OF THE NERVOUS SYSTEM

YOUR BRAIN, YOUR SELF

THOUGHT PROCESSES

THE DYNAMIC BRAIN

BREAKING FROM DOGMA

EMERGING TECHNOLOGIES AND CHALLENGES

Introduction

Modern neuroscience can be traced back to the 1890s, when researchers first determined that the nervous system, like all other living things, is made of cells. Fast-forward a century: President George W. Bush declared the 1990s the Decade of the Brain, and since then research into the workings of this extremely complex organ has accelerated at an astonishing pace. Some say that we have learned more about the brain in the past decade than we did in the hundred years preceding it. Even so, we are only just beginning to scratch the surface, and a huge amount remains to be discovered.

During this short time, many theories about how the brain works, and how it generates our thought and behaviours, have been put forward. Some of the earlier ideas, such as phrenology the 19th-century discipline that tried to correlate personality traits with the shape of the head became influential in their time but were eventually debunked as pseudo-science. Others, such as the neuron doctrine the idea that the brain is made of cells remain central to modern neuroscience.

As technology advances and our understanding of the brain improves, the general public has become increasingly interested in neuroscience and in what these exciting new findings mean for them. At the same time, there is a great deal of sensationalism surrounding brain research, not to mention much inaccurate reporting.

Likewise, myths about the brain abound, and some of the more popular examples such as the idea that the left brain is logical and the right brain creative seem to be gaining traction, especially within education and the business sector.

This book is an attempt to distil over 100 years of thinking about the brain. It draws together influential ideas in neuroscience, updating old concepts in the light of new evidence, as well as introducing others that have emerged only recently. It attempts to explain these ideas accurately, and in a way that is easily digestible; to separate the wheat from the chaff; and to demystify the mysterious matter inside our heads. Where possible, I discuss how the science is carried out the techniques used, and how researchers refine their ideas as new evidence emerges.

Some believe that gaining a better understanding of how the brain works will provide answers to lifes big questions. It will not: brain research cannot tell us everything about ourselves, or what it means to be human. But it does offer the possibility that treatments may be developed for numerous debilitating conditions that afflict us, such as addiction, Alzheimers disease, stroke and paralysis. 50 Human Brain Ideas You Really Need to Know addresses these hopes, too, with cautious optimism.

The nervous system

The nervous system consists of two main components. One part, the central nervous system made up of the brain and spinal cord receives information from, and integrates the activity of, the rest of the body. The other section, the peripheral nervous system, contains nerves that send and receive information to and from the body.

The human brain contains hundreds of billions of cells arranged in a highly organized fashion, and is often said to be the most complex structure in the known universe yet it weighs about only 1.5kg (just over 3lb). It consists of two hemispheres, each of which controls, and receives information from, the opposite side of the body. The cerebral cortex covering each hemisphere is divided into four specialized lobes; these all perform different functions, and are separated from one another by deep grooves called fissures.

• The frontal lobe performs complex mental functions such as reasoning and decision-making, and also contains the motor areas, which plan and execute voluntary movements.
• The parietal lobe contains the somatosensory areas, the parts that process touch information from the body. It also integrates different types of sensory information for spatial awareness basically, knowledge of how the body is oriented within space.
• The temporal lobe receives information from the ears, and its outer surface contains areas specialized for understanding speech. The inner surface contains the hippocampus, which is critical for memory formation and, with the surrounding areas, plays an important role in spatial navigation.
• The occipital lobe is located at the back of the brain and contains dozens of distinct regions specialized to process and interpret visual information.

Layers of complexity The cortex (or bark) is the highly convoluted sheet of folded tissue that sits prominently on the outside of the brain. The cortex of human beings covers a much larger surface area than in other animals extending 0.2m (2 sq ft) if laid out flat. This folding gives the cortex its familiar appearance, with its numerous gyri (bulges) and sulci (furrows). The cortex is just a few millimetres thick, but comprises six layers, with cells arranged uniformly in each layer. Despite this uniform structure, the cortex contains a large number of discrete areas, each specialized to perform a particular function.

The brain uncovered Beneath the cortex lie several large clusters of neurons. The thalamus (or deep chamber) lies right at the brains centre, and relays information from the sense organs to the appropriate region of the brain. Surrounding the thalamus are the basal ganglia, a group of structures involved mainly in the control of voluntary movement. The limbic system is another set of subcortical structures located between the basal ganglia and cortex. Sometimes referred to as the reptilian brain, the limbic system is evolutionarily primitive, and is involved in emotion, reward and motivation. It also includes the hippocampus and amygdala, both of which play a part in memory.

The midbrain is a small area lying at the top of the brain stem. It contains clusters of neurons that control eye movement and is the main source of the neurotransmitter dopamine. Neurons that make dopamine also produce a pigment called melatonin, giving part of the midbrain a black appearance. This part of the midbrain is therefore called the substantia nigra (black substance).

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