10
Electroencephalogram
10.1 INTRODUCTION AND OVERVIEW
The brain acts as the central control and data processing unit for the biological medium. The neural activity of the brain uses action potentials by which the
brain activity can be recorded by means of electrodes, as in electroencephalogram
(EEG), or by magnetic inductors, which form a signal called magnetoencephalogram
(MEG). In this chapter, we focus on the EEG.
Electroencephalogram is the combination of the three words electro, encephalo,
and gram. The first term, electro, pertains to electric and the second term, encephalo,
which stems from the Greek words en-kephale, means “in-head” and stands for the
brain. The third term, gram, represents the act of recording. Putting the three words
together, electroencephalogram means the recording of the electric activities of the
brain.
In 1929, a German psychiatrist named Hans Berger experimented by placing electrodes on the head of his daughter and verified his hypothesis that the brain exhibits
electric activity. He measured the brain waves of his daughter when she was doing
mental arithmetic. He also discovered that the activity increased when she was trying to perform difficult multiplications. From this evidence, he deduced that the wave
patterns observed in the brain recordings reflected the depth of the brain activity.
In this chapter, we focus on the biological roots of EEG as well as the diseases
often diagnosed by analysis of EEG. We also discuss the computational techniques
typically used to process EEG signal.
10.2 BRAIN AND ITS FUNCTIONS
The brain is an organ that is part of the central nervous system (CNS). The brain
monitors and regulates unconscious bodily processes, such as digestion and breathing. The brain also coordinates most voluntary movements of your body. It is also the
site of conscious thinking, allowing you to learn and create. A frontal cross section
of the brain and brain stem is illustrated in Figure 10.1. As can be seen in Figure 10.1,
the gray matter and the white matter form the major part of the brain. The gray matter is the outside shell of the brain and is made up of a body of nerve cells. The nerve
cells (also called neurons) perform the actual signal processing inside the brain. The
white matter in the core of the brain comprises the nerve axons, linking to the gray
matter (cortex), the brain stem, and the peripheral motor and sensory units. Both the
gray and the white matter have connective tissue intertwined for support.
As shown in Figure 10.1, the cortex forms the outside layer of the wavy upper
structure of the brain, which is called the cerebrum. This is where the nerve cells are
located. Below the brain is the cerebellum, which is split into two halves. The cerebral cortex also has two hemispheres. It has been determined that for right-handed
197
Electroencephalogram
10.1 INTRODUCTION AND OVERVIEW
The brain acts as the central control and data processing unit for the biological medium. The neural activity of the brain uses action potentials by which the
brain activity can be recorded by means of electrodes, as in electroencephalogram
(EEG), or by magnetic inductors, which form a signal called magnetoencephalogram
(MEG). In this chapter, we focus on the EEG.
Electroencephalogram is the combination of the three words electro, encephalo,
and gram. The first term, electro, pertains to electric and the second term, encephalo,
which stems from the Greek words en-kephale, means “in-head” and stands for the
brain. The third term, gram, represents the act of recording. Putting the three words
together, electroencephalogram means the recording of the electric activities of the
brain.
In 1929, a German psychiatrist named Hans Berger experimented by placing electrodes on the head of his daughter and verified his hypothesis that the brain exhibits
electric activity. He measured the brain waves of his daughter when she was doing
mental arithmetic. He also discovered that the activity increased when she was trying to perform difficult multiplications. From this evidence, he deduced that the wave
patterns observed in the brain recordings reflected the depth of the brain activity.
In this chapter, we focus on the biological roots of EEG as well as the diseases
often diagnosed by analysis of EEG. We also discuss the computational techniques
typically used to process EEG signal.
10.2 BRAIN AND ITS FUNCTIONS
The brain is an organ that is part of the central nervous system (CNS). The brain
monitors and regulates unconscious bodily processes, such as digestion and breathing. The brain also coordinates most voluntary movements of your body. It is also the
site of conscious thinking, allowing you to learn and create. A frontal cross section
of the brain and brain stem is illustrated in Figure 10.1. As can be seen in Figure 10.1,
the gray matter and the white matter form the major part of the brain. The gray matter is the outside shell of the brain and is made up of a body of nerve cells. The nerve
cells (also called neurons) perform the actual signal processing inside the brain. The
white matter in the core of the brain comprises the nerve axons, linking to the gray
matter (cortex), the brain stem, and the peripheral motor and sensory units. Both the
gray and the white matter have connective tissue intertwined for support.
As shown in Figure 10.1, the cortex forms the outside layer of the wavy upper
structure of the brain, which is called the cerebrum. This is where the nerve cells are
located. Below the brain is the cerebellum, which is split into two halves. The cerebral cortex also has two hemispheres. It has been determined that for right-handed
197