Biology 202
2003 Second Web Paper
On Serendip

Somnambulism, or sleepwalking, belongs to a group of parasomnias. This disorder of arousal is characterized by complex motor behaviors initiated during stages 3 and 4 of non-rapid-eye-movement (NREM) sleep (slow-wave sleep) (3). Behaviors during sleepwalking episodes can vary greatly. Some episodes are limited to sitting up, fumbling and getting dressed, while others include more complex behaviors such as walking, driving a car, or preparing a meal (2). After awakening, the sleepwalker usually has no recollection of what has happened and may appear confused and disoriented. The behaviors performed while sleepwalking are said to be autonomous automatisms. These are nonrelfex actions performed without conscious volition and accomplished independently from the I-function (3). This insinuates that everything done while sleepwalking is involuntary because the exhibited behavior is not a result of the I-function's output. Therefore if the I-function is not involved what causes people to sleepwalk? What happens to the I-function during sleepwalking? What does this imply about brain and behavior?

Sleep is a succession of five recurring stages: four non-REM stages and the REM stage. Researchers have classified these stages of sleep by monitoring muscle tone, eye movements, and the electrical activity of the brain using an electroencephalogram (EEG) (4). EEG readings measure brain waves and classify them according to speed. Alertness consists of desynchronized beta activity whereas relaxation and drowsiness consist of alpha activity (4). Stage 1 sleep includes alternating patterns of alpha activity, irregular fast activity and the presence of some theta activity. This stage is a transition between sleep and wakefulness (4). The EEG of stage 2 sleep contains periods of theta activity, sleep spindles, and K complexes (sudden, sharp waveforms). This stage is believed to help people enter deeper stages of sleep (4). Stage 3 sleep consists of 20-50 percent delta activity and stage 4 sleep of more than 50 percents delta activity (4). Stages 3 and 4 are characterized as being slow wave sleep in addition to being the deepest levels of sleep. Approximately 90 minutes after being asleep, people enter rapid-eye-movement (REM) sleep (4). REM sleep consists of rapid eye movements, a desynchronized EEG, sensitivity to external stimulation, muscle paralysis and dreaming (4).

Sleepwalking occurs during stages 3 and 4 of the sleep cycle, the deepest levels of sleep. This slow-wave sleep is normally characterized by synchronized EEG activity (4). This indicates that mental activity is very low during these stages of sleep. However researchers have shown that the EEG of a sleepwalker has diffuse, rhythmic, high-voltage bursts of delta activity associated with abrupt motor activity (1). This is very different from the EEG activity normally associated with slow-wave sleep. In addition to the EEG results, they found that there is a decrease in regional cerebral blood flow in the frontopariental cortices during sleepwalking (1). This indicates that sleepwalking is a dissociated state consisting of motor arousal and persisting mind sleep, which seems to arise from the selective activation of thalamocingulate circuits and the persisting inhibition of other thalamocortical arousal systems (3).
This study provides several interesting insights into the role of the I-function and its relationship with the nervous system. The results indicate that during sleepwalking there is no input from the I-function due to the lack of strong mental activity in the EEG. Thus the I-function is inactive during slow-wave sleep and somnambulism. The absence of the I-function in slow wave sleep signifies that sleepwalkers despite their outward appearance of being awake are completely unconscious of their actions at the time they are sleepwalking. This also explains why sleepwalkers rarely recall what occurs during a somnambulism episode and often appear disoriented and confused upon awakening.

It is interesting to observe the differences in mental activity between REM sleep and slow wave sleep. They both involve the production of complex behaviors, however REM sleep has a high mental activity associated with dreaming while sleepwalking has very little mental activity (4). Evidence indicates that during REM sleep, the particular brain mechanisms that become active during a dream are those that would become active if the events in the dream were actually occurring (4). For example, McCarley and Hobson, demonstrated that the cortical and subcortical motor mechanisms become active in dreams that contain movements, as if the person were actually moving (5). Therefore in REM sleep the I-function is active and the person is conscious of his/her actions. In somnambulism, the I-function is inactive and the sleepwalker is unconscious of his/her behavior. The sleepwalker is passively producing complex behaviors. These observations indicate that the same outputs are produced using different parts of the brain.

If the I-function is not responsible for the behaviors generated during sleepwalking, what is? The results from the study indicate that the nervous system is responsible for somnambulism. It stimulates the motor outputs seen in sleepwalkers. This indicates that the nervous system can produce behaviors as complex as the ones produced by the I-function. Therefore the I-function is not as influential as it was once thought to be because the nervous system can generate the same outputs with or without its presence. In addition, the study provides evidence that an output can originate within the nervous system without any input from the external environment or the I-function.

The nervous system can function independently from the I-function, but the opposite is not possible. It is able override the I-function and cause people to perform actions that they are unconscious of. This leads me to believe that the nervous system plays a greater role in our behavior than our I-function does.

Somnambulism is a fascinating behavior. It is induced by a dissociation between mental and motor arousal (1). It provides good insight into the correlation between the nervous system and the I-function. Sleepwalking demonstrates that the nervous system is capable of performing behaviors similar to those specified by the I-function and that it can function independently from it. Despite my greater understanding of somnambulism I was unable to determine why the nervous system causes people to sleepwalk. It has been shown that no dreaming occurs during these stages of sleep. Therefore I do not understand what sleepwalkers acting out. This question still remains open for investigation.

Works Cited

1)Bassetti, C., Vella, S., Donati, F., Wielepp, P. Weder, B. SPECT during sleepwalking. Lancet 2000 Aug 5; 356(9228):484-85

2)3)Masand, P., Popli, A., Weilburg, J. Sleepwalking. American Family Physician 1995. v5 n3 p649.

4)Carlson, N. Physiology of Behavior. 7th ed. Allyn and Bacon. USA, 2001

5)McCarley, R.W. and Hobson, J. A. The form of dreams and the biology of sleep. In the Handbook of dreams: Research, Theory, and Applications, edited by B. Wolman. New York: Can Nostrand Reinhold, 1979.


| Course Home Page | Course Forum | Brain and Behavior | Serendip Home |