Genes, Brain Function, and Behavior

What Genes Do, How They Malfunction, and Ways to Repair Damage

Douglas Wahlsten

• Publisher: Academic Press
• Year: 2019
• Print ISBN: 9780128128329
• eBook ISBN: 9780128128336
• Topic: Biological Sciences
• Subtopic: Neuroscience
• Index: Biological Sciences

Genes, Brain Function, and Behavior offers a concise description of the nervous system that processes sensory input and initiates motor movements. It reviews how behaviors are defined and measured, and how experts decide when a behavior is perturbed and in need of treatment. Behavioral disorders that are clearly related to a defect in a specific gene are reviewed, and the challenges of understanding complex traits such as intelligence, autism and schizophrenia that involve numerous genes and environmental factors are explored. New methods of altering genes offer hope for treating or even preventing difficulties that arise in our genes. This book explains what genes are, what they do in the nervous system, and how this impacts both brain function and behavior.- Presents essential background, facts, and terminology about genes, brain function, and behavior- Builds clear explanations on this solid foundation while minimizing technical jargon- Explores in depth several single-gene and chromosomal neurological disorders- Derives lessons from these clear examples and highlights key lessons in boxes- Examines the intricacies of complex traits that involve multiple genetic and environmental factors by applying lessons from simpler disorders- Explains diagnosis and definition- Includes a companion website with Powerpoint slides and images for each chapter for instructors and links to resources

Chapter 1

Levels and Explanations

Abstract

Genes are large molecules that interact with other large molecules. Several kinds of molecules join together to form complex organelles that have well-understood functions, such as the synapse that enables communication between nerve cells. Putting together thousands of synapses and other parts such as axons with myelin sheaths, we arrive at the level of an entire neuron, the building block of a nervous system. Assembling networks of neurons into a nervous system, we approach the level of an entire organism that can perform many kinds of behavior. Behavior is a property of a whole individual living in a society. Genes cannot code for any specific behavior. Instead, they code for discrete steps in localized chemical reactions. They are small parts of a much larger system of molecules.

Keywords

Genotype-phenotype; Organelle; Size and connections; Gene-environment interaction; Organism in society

Understanding the relations between genes, the brain, and human behavior is a very challenging task because the three things exist at different levels (Table 1.1). Behavior and thinking are done by an individual, a whole person. The science of psychology teaches us how to define and measure mental functions and behaviors. Genes, on the other hand, are molecules contained in the nucleus of almost all cells in the body (except red blood cells). A gene, part of a DNA molecule, codes for the structure of another kind of molecule, a protein, which is a long chain of smaller amino acid molecules. The study of genes and the inheritance of DNA molecules is the domain of genetics. The genes transmitted from parents to offspring constitute the person's genotype, whereas the characteristics that are measured constitute the phenotypes, and phenotypes can exist at several levels.

Table 1.1

Levels of Explanation and Scientific Disciplines

Level	Examples	Specialty
Geographic cluster	Village, province, nation	Political science
Social organization	Family, club, orchestra, hospital	Sociology
Individual	Fruit fly, mouse, dog, human being	Psychology
Organ	Eye, brain, ovary, arm	Physiology
Tissue	Retina, gums, bicep muscle	Physiology
Cell	Neuron, leucocyte, sperm	Cell biology
Organelle	Synapse, myelin, mitochondria	Neurobiology
Macromolecule	DNA (gene), protein, omega-3 fatty acid	Biochemistry, genetics
Molecule	Water, carbon dioxide, ethanol, lysine	Chemistry
Atom	Carbon, hydrogen, oxygen, iron, silver	Physics

Once we have a fairly good idea of how the gene works and what its protein product does, we can then begin to understand how it might be involved in brain function and behaviors. Hopefully, we will also gain some good ideas about how to ameliorate the effects of a defective gene by making adjustments to the environment or devising new medical treatments. This book explains how genes are related to thought and behavior by exploring examples in which the role of a specific gene is quite well understood. The examples show how a gene can influence behaviors, even though it does not code specifically for those behaviors. The concept is not an easy one to grasp. Real examples can guide us to a better understanding of difficult concepts.

Levels and Scientific Disciplines

The concept of integrative levels has been applied in different ways by different fields of science, as described in a historical review by Kleineberg (2017). Here, the concept is applied to things that differ in size and the kinds of connections within and between the levels. An entity at one level is made up of several smaller things at the next lower level that are connected and work together. Small molecules such as water or ethanol are composed of two or more kinds of atoms connected by chemical bonds (Fig. 1.1). Macromolecules such as proteins are made up of long chains of smaller molecules known as amino acids, each of which is made of hydrogen, carbon, oxygen, nitrogen, and sometimes sulfur. Organelles are built from several kinds of macromolecules, while an entire cell such as a neuron in the brain contains many types of organelles. Several kinds of cells unite to form a specific tissue, such as the quadriceps muscle in the leg, and an assemblage of different tissues forms an organ—a liver or a brain. Combining the brain with other essential organs such as the heart, lungs, eyes, and hands, we arrive at an entire organism, the individual person, who in turn is part of a social group. The brain itself does not express behavior; it does not move. The brain itself cannot think; it needs connections with sense organs and a long tutoring in language to engage in thought and express ideas to other members of a social group. The whole person thinks and speaks. Only as parts of a social group do people have anything to say.

Fig. 1.1 Atoms of carbon, hydrogen, and oxygen are shown as the letters C, H, and O, respectively. Chemical bonds are shown as small lines, and a double bond is two lines. Hydrogen can form just one bond, oxygen two, and carbon four. (A) When each atom of H or O is bound to another of the same kind, the two kinds form a mixture of gases. When a spark triggers oxidation of the hydrogen, the result from the same atoms arranged differently is liquid water. (B) The isomers ethyl alcohol and dimethyl ether both have the chemical formula C₂H₆O, but the properties of the molecules differ greatly when the oxygen is in a different position.

Because the levels of reality are so different, specialized disciplines have arisen to study and explain them. Physics studies atoms such as carbon and oxygen, but it cannot tell us much about the properties of macromolecules such as genes or proteins. To be a good physicist, a scholar does not need to know anything at all about genes. Likewise, a geneticist will not be able to explain inheritance by doing an in-depth investigation of the nitrogen atom or the electron. There are many commonalities across levels in the fundamental methods of doing a scientific study and analyzing the data with mathematics, and a few broad generalizations about nature can also be made. Nevertheless, the large bulk of knowledge of a specific level is encapsulated in the texts and journals of a specific discipline.

A few hybrid disciplines span several levels. Neuroscience is a prime example. Molecular neuroscience examines how small neurotransmitter molecules such as dopamine are synthesized by large macromolecules called enzymes and stored in an organelle, a synapse that connects two neurons (Fig. 1.2). The enzymes needed to make dopamine arrive in the synapse, and the transmitter molecules that they synthesize are then stored in small vesicles. Things happen in the person's environment that can stimulate the release of dopamine from the vesicles and deliver a pulse of chemical energy that influences the next nerve cell in a circuit. If enough neurons get involved in the action, this can change the individual's behavior. Thus, a student of neuroscience needs to study sciences at different levels from molecule to mind in order to achieve a good understanding of...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Author Biography
• Preface
• Acknowledgments
• Chapter 1: Levels and Explanations
• Chapter 2: Genes
• Chapter 3: Gene Expression
• Chapter 4: The Nervous System
• Chapter 5: Development
• Chapter 6: Behavior
• Chapter 7: Single-Gene and Chromosomal Disorders
• Chapter 8: Phenylketonuria (PKU)
• Chapter 9: Huntington Disease
• Chapter 10: Androgen Insensitivity Syndrome (AIS)
• Chapter 11: Leber's Optic Neuropathy
• Chapter 12: Down Syndrome
• Chapter 13: The XYY Male
• Chapter 14: Complex Traits
• Chapter 15: Intelligence
• Chapter 16: Autism
• Chapter 17: Schizophrenia
• Chapter 18: Sexuality and Gender
• Chapter 19: Race
• Chapter 20: The Future
• Index