Very few functions of the nervous system have been worked out to the point of identifying the underlying neuronal networks. The processes responsible for the higher brain functions discussed in the remaining pages of this chapter are undeniably complex. Nevertheless, neurobiologists, using a wide range of techniques, are making considerable progress in understanding some of the cellular and molecular mechanisms involved in those processes. The following discussion presents several complex aspects of brain and behavior that present challenges to neurobiologists: sleep and dreaming, learning and memory, language use, and consciousness.
Sleep and dreaming produce electrical patterns in the cerebrum
A dominant feature of human behavior is the daily cycle of sleep and waking. All birds and mammals, and probably all other vertebrates, sleep. We spend one-third of our lives sleeping, yet we do not know why or how. We do know, however, that we need to sleep. Loss of sleep impairs alertness and performance. Most people in our society—certainly most college students—are chronically sleep-deprived. Large numbers of accidents and serious mistakes that endanger lives can be attributed to impaired alertness due to sleep loss. Yet insomnia (difficulty in falling or staying asleep) is one of the most common medical complaints.
the electroencephalogram. A common tool of sleep researchers is the electroencephalogram (EEG). To record an EEG, electrodes are placed at different locations on the scalp, and changes in the electric potential differences between electrodes are recorded over time. These electric potential differences reflect the electrical activity of the neurons in the brain regions under the electrodes, primarily regions of the cerebral cortex. Pens writing on a moving chart are used to record the patterns of these differences (Figure 46.13a,b). Usually, the electrical activity of one or more skeletal muscles is also recorded on the chart; this record is called an electromyogram (EMG).
EEG and EMG patterns reveal the transition from being awake to being asleep. They also reveal that there are different states of sleep. In mammals other than humans, two major sleep states are easily distinguished: They are slow-wave sleep and rapid-eye-movement (REM) sleep. In humans, we characterize sleep states as non-REM sleep and REM sleep. Human non-REM sleep is divided into four stages. Only the two deepest stages are considered true slow-wave sleep.
When a person falls asleep at night, the first sleep state entered is non-REM sleep, which progresses from stage 1 to stage 4. Stages 3 and 4 are deep, restorative, slow-wave sleep. This first episode of non-REM sleep is followed by an episode of REM sleep. Throughout the night, we experience four or five cycles of non-REM and REM sleep (Figure 46.13c). About 80 percent of our sleep is non-REM sleep, and 20 percent is REM sleep.
46.13 Patterns of Electrical Activity in the Cerebral Cortex Characterize Stages of Sleep
(a) Electrical activity in the cerebral cortex is detected by electrodes placed on the scalp and recorded on moving chart paper by a polygraph. (b) The resulting record is an electroencephalogram (EEG). (c) During a night, humans cycle through different stages of sleep.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.