The state of consciousness one is in — whether a normal or an altered state — depends on brain activity. In fact, electrical activity in the brain is an important indicator of the different parts of sleep (see Section 2-6). The relation between brain activity and states of consciousness is one piece of evidence for what I will refer to as the brain-mind theory — the theory that states that human cognitions, emotions, and behaviors are caused most directly (most proximally) by activity of the nervous system. Note that this theory makes a claim that is more than stating that brain activity and mental/behavioral activity are related: it states that brain activity causes mental and behavioral activity.

Some of the evidence for the brain-mind theory comes from observations made beginning about 1860 that showed that specific impairments in mental/behavioral functioning were linked to damage to specific areas of the brain. To take just one example, the neurologist, Oliver Sacks (1995), described a man who had a large part of his brain destroyed by a benign[∂] tumor. While the tumor was growing and after it was removed in 1975, this man — to whom Sacks gave the pseudonym[∂], “Greg” — exhibited many problems often seen in others who have experienced brain damage to the same area. For example, Greg became blind and obese, lost all his hair, and often made bizarre comments. Furthermore, he did not seem to know where he was or what the date was. In fact, he believed that he was living in the late 1960s — a time period during which he had been a teenager. He had been heavily involved in the "hippie culture" during that time, taking drugs and eventually devoting himself to the practice of an Eastern religion. Sacks first met Greg in 1977:

Lacking facial hair, and childlike in manner, he seemed younger than his twenty-five years. He was fat, Buddha-like, with a vacant, bland face, his blind eyes roving at random in their orbits, while he sat motionless in his wheelchair. If he lacked spontaneity and initiated no exchanges, he responded promptly and appropriately when I spoke to him, though odd words would sometimes catch his fancy and give rise to associative tangents or snatches of song and rhyme. Between questions, if the time was not filled, there tended to be a deepening silence; though if this lasted for more than a minute, he might fall into Hare Krishna chants or a soft muttering of mantras. (p. 45)

Greg's amnesia[∂] was so severe that he seemed to have forgotten much of what had happened to him beginning in about 1968: he was unable to remember anything for more than about 20 seconds after its occurrence. In short, Greg’s brain tumor and its removal caused severe and permanent impairments physically, behaviorally, and psychologically. These impairments were linked directly to the specific areas damaged by the tumor — areas that are damaged in others showing the same impairments — which is what one would expect to find if the brain-mind theory were true.

In a previous section, you learned that scientific theories must be supported by evidence. This evidence is obtained by:

• deriving predictions from a theory;
• making observations that either confirm or disconfirm these predictions.

Good theories are ones that lead to many confirmed predictions and few disconfirmed predictions. The brain-mind theory has been confirmed by a very large number of observations over the last 150 years. In fact, the brain-mind theory is so well supported that many neuroscientists consider it to be a fact: a true theory. In other words, patterns of electrical activity in the central nervous system (CNS) — which consists of the brain and spinal cord — and in the peripheral nervous system (PNS) — which consists of the nerve pathways leading to and from the CNS — are the most direct (proximal) causes of our cognitions, emotions, and behaviors.

Measuring Brain Activity

When performing research on altered states of consciousness, researchers often measure brain activity and correlate it with changes in the state of consciousness. A correlation is an estimate of the degree to which two things are associated — the degree to which they change together. For example, there is a correlation between the number of hours spent studying for a test and test scores: on average, the more time spent studying, the higher the score. In this example, as one factor gets larger (the amount of time spent studying), the other factor gets larger (test scores). This is called a positive correlation. There also is a correlation between the amount of time spent watching television and test scores: on average, the more time spent watching TV, the lower the score. In this example, as one factor gets larger (the amount of time spent watching TV), the other factor gets smaller (test scores). This is called a negative correlation. You''ll learn more about correlations and correlational studies in Section 3.

Modern correlational studies of brain activity allow researchers to link activity in particular brain structures with changes in particular mental and behavioral functions. For example, people who have had a stroke often develop localized brain damage: the disruption of blood flow to and from a location causes the death of brain cells at that location. The death of brain cells often correlates with changes in mental and behavioral functioning, such as difficulties with speaking, writing, reading, or understanding the speech of others.

In general, there are two types of correlational study used to locate brain areas associated with mental and behavioral functioning.

1. In a damaged brain, researchers correlate the amount and location of damage with the severity of mental and behavioral abnormalities. In order to use this method, we need to be able to see the structures that make up the nervous system. Autopsies may be performed after neurological[∂] patients die in order to locate damaged areas of the nervous system. There also are several techniques that allow us to get pictures of the nervous systems of living subjects. Although X-rays have often been used for this purpose, especially in the past. there now are much better techniques available — techniques that give much clearer pictures of the nervous system (such as magnetic resonance imaging, or MRI).
2. In an undamaged brain, researchers correlate the degree of abnormal neural[∂] activity with the severity of mental and behavioral abnormalities. The brain works because of biochemical activity in the billions of cells, called neurons, that make up the brain. These biochemical changes cause electrical activity within and between neurons (see Section 4-12). Researchers look for abnormalities of biochemical or electrical activity in specific areas of people's brains, and correlate this activity with mental/behavioral abnormalities.

To measure brain activity, beginning in the 1930s, sleep researchers used a device called an electroencephalograph (EEG), which is now a somewhat primitive method for measuring changes in the electrical activity of neurons, although it still often is used in research. The EEG is limited in two ways. First, it is able to measure the electrical activity of only those neurons in the upper layers of the cerebral cortex (the outermost layer that makes up most of the human brain; the wrinkled part that you see when you look at a brain), which means that it is unable to measure activity in most of the brain. Second, it is unable to measure the activity of single neurons: it measures the summed electrical activity of millions of neurons.

Nevertheless, since about 1920, the EEG has helped brain researchers measure mental states and is still used to diagnose neurological disturbances in individuals. Right now, if you were hooked up to an EEG machine, you would exhibit a high level of electrical activity in your cortex. If you were in a coma, on the other hand, you would show a low level of electrical activity in your cortex. The EEG transforms this electrical activity into wave patterns that, before the advent of computers, typically were traced onto rolling sheets of paper. These tracings are referred to as brain waves. Changes in a person's state of arousal — from being awake and alert to deeply asleep — are associated with changes in brain waves. The following list describes some of the more common types of brain waves along with the state of consciousness which each typically (but not always) is associated with:

(1) Beta waves show that a person is actively attending to events and, therefore, is aware of what is happening around him or her.
(2) Alpha waves show that a person is awake but is not actively processing visual information. Alpha waves generally are observed when the person is relaxed and inattentive, such as when daydreaming or just before falling asleep.
(3) Theta waves are observed when a person has fallen into a light sleep — a stage of sleep from which he or she can be awakened easily.
(4) Delta waves are observed when a person has entered deep sleep — a stage of sleep from which he or she cannot be awakened easily.

These four brain-wave patterns are illustrated in Figure 1.

Figure 1. Some of the Brain Waves Commonly Measured in Sleep Research
(From Tortora & Grabowski, 1996, p. 414).

Study Questions for Section 2-5

1. What is the brain-mind theory?
2. What is some evidence supporting the brain-mind theory?
3. What is some supporting evidence from your own life for the brain-mind theory?
4. Is the brain-mind theory a "good theory"? Why or why not?
5. What is a correlation?
6. What is a positive correlation?
7. What is an example of a positive correlation from your own life?
8. What is a negative correlation?
9. What is an example of a negative correlation from your own life?
10. What are the two types of correlational study used in brain research?
11. What is the EEG and what is it used for?
12. What are the four types of brain wave mentioned in this section and what mental state is each correlated with?

Go to Quiz 2-5 questions

Go to Readings Section 2-6