My grandmother, a no-nonsense New England woman, sometimes described a man as “in the brown cabinet.” This is an English idiom, not often used today, that describes a person who is serious (the “study” part of the phrase), a little sad (“brown”). According to him, this person is wasting time with dreams that should be engaged in some productive work. It turns out that the grandmother may have been wrong – this dream can be very effective.
The reason for useful dreams lies in another idiom that you are more familiar with, and this is advice to “sleep” on an idea before deciding what to do with it. This phrase comes from the ancient idea (dating back to the 1500s) that sleep helps us make better decisions (The Idioms, n.d.). The benefits of sleep for memory have a long history in science. However, as our understanding of the complexity of sleep has grown, so have our questions about how sleep helps us solve the problem. Stickgold (2005) notes that the turning point in the study of sleep and memory was a 1994 “seminal paper by Carney, Sagi, and colleagues.” This study found that memory formation depends on rapid eye movement (REM or). to dream) sleep. Many studies have confirmed this idea.
One of the challenges facing researchers is that sleep is as complex as memory. Just as there are several types of sleep that involve different brain systems (dreaming or REM sleep and non-dreaming slow-wave sleep), there are also several different types of memory that use different but overlapping parts of the brain. There are two broad categories of memory: declarative (memories that we can talk about mainly using language) and non-declarative (memories that are difficult to use language). Remembering facts like the name of your country’s capital is called semantic declarative memory. Memory for a specific event in your life and the context for that event is called episodic declarative memory. Memory for things like how to ride a bicycle is a form of non-declarative memory (there are other forms) called procedural memory.
Memories go through the process of “consolidation” in the brain, which means that they are stable, resistant to interference and long-term. Memory consolidation occurs over time, regardless of the type of memory, and traditionally, according to models of the role of sleep in memory formation, REM sleep is particularly important in this process. Current thinking suggests that memories are consolidated in a structure called the hippocampus, a process that reactivates its pattern. neuron shooting during the initial experience of the event. For example, consider what is called “place learning” in the rat.
When a rat learns to navigate a maze, the cells in the hippocampus form a pattern that repeats the route required to reach the goal (reward), called “array cells.” Place the cells in specific areas of the local environment. The location of cellular responses is initially temporarily stored in the hippocampus. When the mouse sleeps, this place cell response ensemble is reactivated, which strengthens the connections between the cells. Eventually, through repeated reactivation of the pattern, the now very strong memory of the route through the maze is sent to the cortex for long-term storage.
At first, researchers thought that this reactivation of cellular responses occurred only during sleep. Recent studies have shown that reactivation occurs when we are awake and at rest, even when we are dreaming. FMRI studies have shown that this occurs in rats after maze training, as well as in humans (Tambini and Davachi, 2019), both in the hippocampus and in various regions of the cortex. long term memory storage
The tasks the subjects were asked to complete were somewhat more complex than the relatively simple mazes used to test rodents. For example, Schuck and Niv (2019) investigated reactivation responses in the human hippocampus using fMRI. Their participants saw composite images of faces (young and old) and houses (also young and old) and were asked to estimate the age of the face or the house. They were able to show that the resting-state response patterns of the hippocampus following the task mirrored the activity seen during this abstract, non-spatial task. decision making task
Using reinforcement learning that occurs in a fearful situation, de Voogd, Fernández, and Hermans (2016) asked their participants to view pictures of animals or plants. Baseline recordings were made while participants viewed all images. Fear training began with 50% of images from one category (e.g., plants category) paired with a light shock (CS+ condition). Half of the participants tested the CS+ with images of plants and the other half with images of animals. The next day, four pictures from each category were presented, no shocks occurred, and records were taken. They found “spontaneous reactivation of category-specific patterns during waking rest following learning for a conceptual category associated with an emotionally arousing event.” Pairing the shock with plants created a memory of plants as fearful stimuli.
Examination of the processes used in the consolidation is ongoing. Evidence is mounting that daydreaming is more than just a waste of time. When we dream we may be actively working to remember what happened to us today.
