Our understanding of human biology has come a long way in the last century. However, progress in our understanding of dreams has been very slow. The biological function of dreams is a gray area. The only certainty is that most humans dream regularly.

The stage of vivid dreaming sleep is called REM (rapid eye movement) sleep. People who wake up during this stage of sleep often report that they were dreaming. Rapid eye movements are a puzzle for researchers because they are difficult to measure.

Recent reports ( chemistry roll. 377, 2022) addressed the question of whether eye movements are related to what is happening in dreams. Can motion carry information about dreams that can be analyzed and interpreted?

dream interpretation

But first, some background on dream interpretation. The early 20th century was dominated by Sigmund’s Freudian theory, which focused on the symbolic meaning of images evoked from dreams. With the discovery of REM sleep in 1952, the departure from psychoanalysis began.

It turns out that the brain during REM sleep is as active as it is in a state of full wakefulness. REM sleep is found in all mammals and birds. Michel Jouvet has shown that damaging the cat’s brain stem frees the cat from its bodily immobility in the dream state. This cat would fight loudly with another cat and stop when he woke up.

Electroencephalogram (EEG) recordings provided fresh insights. These recordings showed little difference between REM sleep and wakefulness. Even more amazingly, neuroscientist Matthew Wilson recorded brain activity in rats exploring a maze, and shortly thereafter acquired the same brain waves when the same rats were in REM sleep. Are you solving mazes in your dreams?

dream database

Another way to study dreams was to compile vast databases of dreams. After analyzing 50,000 dreams, they concluded that most dreams did not resemble surrealist paintings and were fairly predictable. Children tend to dream of animals, so while children may smile while dreaming, adults’ dreams were not very pleasant and were often filled with unsettling moments.

We worry about something important, something that needs to be resolved. A theory put forward by Francis Crick and Graeme Mitchison states that dreaming acted as a housekeeping function, sorting out the events of that particular day each night. During classification, some significant events (potentially anxiety-causing) were stored as memories and the rest were treated as clutter.

Are there real-time outputs from dreams that can be recorded? The results are conflicting. Several studies have shown that either the direction or frequency of eye movements is consistent with mental processes recalled in dreams. Electrooculography (EOG) was used to record eye movements in sleeping human volunteers. This recorded whether eye movements were primarily vertical (up and down) or horizontal (left and right). Rapid eye movements recorded were up and down if the volunteer reported looking up in the dream.

Other studies have attributed REM to random activity in the brain.

Strategy practice

When we are awake, we need eye movements to survive. Rats in the field frequently raise their eyes to scan the sky for bird hazards. Human pedestrians perform left and right scans and watch out for oncoming traffic. In both cases the eyes move in the same direction as the head. Your brain uses nerve cells called Head Direction (HD) cells to track which direction your head is facing. In mice, using electrodes inserted into HD cells, these cells have been shown to be active during head movement.

Senza and Scanziani recorded the activity of both REM and HD cells in sleeping mice. Strikingly, they showed that mice in REM sleep make up-and-down eye movements that resemble daytime sky scans. The HD cells also showed corresponding movements, but the mouse was asleep and the head itself did not move.

Can these studies be used to benefit humans? People who experience sudden and intense trauma suffer from PTSD (post-traumatic stress disorder). A soldier shocked by a grenade exploding right behind him, otherwise unharmed, can experience recurring nightmares and anxiety for years. What does he “see” every night? Better understanding leads to better rehabilitation strategies.

( This article was written in collaboration with molecular modeling researcher Sushil Chandani. ushilchandani@gmail.com)