Normal sleep patterns

Sleep can be assessed by measuring the electrical activity that occurs in the brain. We normally undergo several cycles during the night moving through the various stages of sleep. Sleep can be divided into a number of different stages. People tend to go through stages 1 to 4 when they are falling asleep and the reverse when they are waking up. Stages 1 and 2 are regarded as light sleep. Stages 3 and 4 are deep sleep. There is also a fifth stage and it is called the rapid eye movement sleep (REM) because although our eyes remain shut, they move around a lot during this stage. REM sleep is the time during which we have dreams.

REM (Rapid Eye Movement) Sleep

1. REM begins typically after about 90 minutes into sleep.
2. It occurs throughout the night on a 90-100 minute cycle
3. Polygraph measurements during REM sleep appear very similar to those taken of the person in the waking state
4. Vital signs such as pulse rate, ventilation rate and blood pressure are all comparatively high during REM sleep
5. Brain oxygen demand increases above that of supply
6. Body temperature regulation is altered
7. Depressed people demonstrate changes in REM sleep. REM occurs earlier and mostly occurs to the latter half of the period of sleep.
8. Someone waking from REM sleep will usually do so rapidly and report that they were experiencing dreaming.
9. As a person gets older the percentage of time spent in REM sleep decreases.

Non-REM Sleep

1. The pulse rate typically slows by 5-10 beats per minute; ventilation and blood pressure also drop and unlike in REM sleep is stable and regular.
2. Episodic, involuntary movements occur - similar to the jumping/falling movements some people will be familiar with.
3. Someone waking rapidly from deep non-REM half to one hour into sleep will be disorientated and possess disorganized thinking and will be slow in returning to baseline consciousness/cognition.
4. Thus it is suggested (Kaplan) that awaking from deep non-REM sleep will result in specific disorders resulting from the disorientation experienced, such as bedwetting, somnambulism and nightmares.
5. Cerebral blood flow in non-REM sleep is reduced, as it is too almost all body tissues.
6. In the healthy adult, non-REM sleep accounts for 75 percent  of sleep time.

Sleep patterns in depression

The sleep patterns in a person with depression are very different from the normal sleep patterns:

• It takes much longer to get off to sleep.
• The total sleep time is reduced.
• There is little or no deep sleep.
• REM sleep occurs earlier in the night.
• There are more frequent wakenings during the night
• The person wakes up earlier in the morning.

Pathophysiology of somnambulism

Experts are saying that sleepwalking occurs most often at a certain point in the sleep architecture. Various research has proven that this happens at the point where the sleeper's brain waves become larger during the passing into deeper sleep. The patient can also have other REM disorders or psychiatric and medical disorders which do not account for the sleepwalking.

While sleepwalking, the patients' brainwaves show a mixture of types of brainwave patterns, including ones similar to those observed in waking patients, as well as those found in deep sleep.

The exact pathophysiological mechanism is not fully understood, but it involves a partial arousal in the brain where the frontal lobes, responsible for executive functions and decision-making, remain asleep, while the motor cortex, brain stem, and central pattern generators, which coordinate movement, are active. This disconnection results in the performance of movements that are typically automatic or semi-purposeful without conscious awareness or full alertness.

Genetic predispositions can play a role, as sleepwalking is more common in individuals with a family history of the condition. Other contributing factors may include sleep deprivation, febrile illnesses, stress, alcohol, and certain medications that affect the central nervous system. Neuroimaging and electrophysiological studies show abnormal activation in areas controlling locomotion and consciousness during somnambulistic episodes, indicating a complex interplay between neurochemical, genetic, and environmental factors in the manifestation of somnambulism.