Parts of the Brain Involved in Dreaming

Dreams occur mostly in rapid eye movement (REM) cycles, but they can happen in other sleep phases as well. There are various theories about the purpose of dreaming, but no one knows for sure why humans dream. However, the physical process of dreams is observable. In an effort to understand dreaming, researchers have done positron emission tomography (PET) scans to observe brain function in dreaming subjects.

Pons

• The pons is an area of the brain stem that paralyzes the skeletal muscles during REM sleep. This allows the brain to have realistic dream experiences without acting them out in the physical world. Because of the pons, sleepwalking only occurs in non-REM sleep phases.

Sensory Areas

• After the pons paralyzes the dreamer, dream activity begins in the lateral geniculate bodies and the occipital cortex, which are involved in vision. Blind people who were born blind or lost their sight very early have no visual dreams, while the blind who lost sight later in life retain visual dreams. This suggests that the visual component of dreams is linked to visual memory.

  Occipital cortex activity is not as high during dreaming as it is during waking hours. However, the adjacent regions of the brain, which process visual signals, display a high level of activity. In 2004, a stroke victim lost the ability to dream after she suffered damage to areas of her brain that handled the processing of landmarks, faces and other visual signals, suggesting that these areas are vital to the overall dreaming process.

  After the occipital cortex is activated, other areas of the brain, including the cerebral cortex and the thalamus, begin to show activity. This is that stage of the dream that begins to incorporate movement and the sense of hearing and touch. The areas of the brain that respond to smell and taste are not activated during dreaming, and these sensations rarely appear in dreams.

Limbic System

• The limbic system is the center of emotions in the brain, and it is highly active during dreaming. This means that when you feel an emotion while dreaming, your brain processes that emotion in the same way that it would if you were awake. It is unclear whether dreams are often highly emotional because of the activity in this area, or the activity is due to the dream content, which has another source.

Prefrontal Cortex

• The prefrontal cortex exhibits decreased activity during dreams. Its lack of activity facilitates dreaming as we know it. The prefrontal cortex is the region of many higher functions, including logic and planning. During dreams, it keeps quiet about absurd plot twists that it would call attention to in waking life. Instead, it allows the dreamer to participate in the dream without worrying about what will happen next.