Dreaming and Memory

As I am writing this, one of the cats is fast asleep on my desk and clearly involved in a dream that involves running and jumping. It looks as if she’s having fun.

I’ve been fascinated by dreams and dreaming ever since I read Sigmund Freud’s The Interpretation of Dreams as a teenager. For over a century, people have speculated about a link between dreams and memory, and another book that influenced me as a youngster was called Dreaming and Memory by Stanley R. Palumbo. These books were firmly rooted in a psychoanalytic framework, and I’ve always been interested in trying to reconcile psychoanalytic and neurological views of our mental life.

So I was intrigued to see an article that just came out in Nature Neuroscience.

Almost six years ago, Matthew A. Wilson at the Massachusetts Institute of Technology (MIT), in Cambridge, Massachusetts demonstrated something very interesting. Rats formed complex memories for sequences of events that they had experienced while they were awake. These memories were replayed while they slept, perhaps reflecting the animal equivalent of dreaming.

These replayed memories were detected in the hippocampus, a region of the brain that is associated with memory. But the researchers were not able to determine whether they were accompanied by the type of sensory experience that we associate with dreams-in particular, the presence of visual imagery.

In the latest research Wilson who is professor of brain and cognitive sciences at MIT’s Picower Institute for Learning and Memory, and postdoctoral associate Daoyun Ji looked at what happens in rats’ brains when they dream about the mazes they ran while they were awake. They recorded brain activity simultaneously in the hippocampus and the visual cortex, and  demonstrated that replayed memories did, in fact, contain the visual images that were present during the running experience. Neurons that are activated when the animal experiences an event while awake are reactivated during sleep.

There is another piece to this research: the regions of the cerebral cortex that processes input from the senses and the hippocampus communicate with each other during sleep, leading us to speculate that this process reinforces and consolidates memories.

As the authors write, "These results imply simultaneous reactivation of coherent memory traces in the cortex and hippocampus during sleep that may contribute to or reflect the result of the memory consolidation process."

This is of great practical importance: it strongly supports the idea that adequate sleep is necessary to consolidate memory.

When I was a child my parents taught me to read through all my schoolwork just before I went to bed, even if I was tired. Work in psychology has shown that this is often the best way of memorizing factual material, and this new research shows us why.

“Waking is long and a dream short; other than this there is no difference. Just as waking happenings seem real while awake, so do those in a dream while dreaming. In dream the mind takes on another body. In both waking and dream states thoughts, names and forms occur simultaneously.”
–Ramana Maharshi (Indian Hindu Mystic and Spiritual Teacher, 1879-1950)

“The light of consciousness passes through the film of memory and throws pictures on your brain. Because of the deficient and disordered state of your brain, what you perceive is distorted and colored by feelings of like and dislike. Make your thinking orderly and free from emotional overtones, and you will see people and things as they are, with clarity and charity.”
— Sri Nisargadatta Maharaj (Indian Spiritual Teacher and Exponent of Jnana Yoga and Advaita Doctrine, 1897-1981)