I’ll go along with that. But my wish list contains a few more items:
- A better memory for past events is one. My husband narrates whole sequences of his childhood as though he were reliving them again. My memories are skeletal by comparison.
- I’d also like to remember my dreams. My husband recalls entire movies that take place nightly in his head, but I’m lucky if I remember a snippet of a dream once in 3 weeks.
Research suggests that insomnia may have negative effects on memory, and also that the consolidation of memories for facts and events takes place largely during deep sleep, when slow brain waves predominate. Now a team of Italian researchers is claiming in a review paper that theta waves—which are slightly faster—are likewise important in the formation and recall of memories, for both waking events and dreams.
Types of Brain Waves
Day and night, neurons are firing in the brain at a mix of frequencies. When we’re alert, most neuronal activity taking place is fast, or high frequency. (Frequency is measured in cycles per second, or Hertz [Hz]). At night the brain slows down. But activity picks up again during rapid eye movement (REM) sleep. Here are the 5 types of brain activity:
- Gamma waves, 40 to 100 Hz. Associated with intensely focused attention and effortful problem solving.
- Beta waves, 15 to 40 Hz. Associated with a more relaxed but focused level of attention, thinking, and sensory processing.
- Alpha waves, 8 to 14 Hz. Associated with resting, relaxation, and meditation. Also the starting point for falling asleep.
- Theta waves, 4 to 7 Hz. Predominant during Stage 2 sleep. May also occur during very relaxed periods of wakefulness, when the mind is wandering.
- Delta waves, 0.5 to 3.5 Hz. Predominant during deep sleep.
The mixed-frequency brain activity that occurs during REM sleep—theta, alpha, and beta—makes it look like the brain is more awake than asleep.
Theta Waves Involved in Waking Memory
Research shows that memory processing is characterized by specific waveforms occurring in memory-related areas of the brain. In particular, the Italian researchers write, the theta rhythm “seems to correlate consistently with episodic memory, . . . the ability to remember past experiences and autobiographical events.”
Memory processing involves both inner and outer areas of the brain, and EEG recordings of subjects performing cognitive tasks have shown that theta power increases in key areas during the encoding and retrieval of information. In two studies, participants were exposed to a series of words and then asked to recall them later. The authors found that (1) theta power increased only during the encoding of the items that participants were later able to recall, and (2) the amount of theta power during the encoding phase differentiated good and bad performers when it came time to recall what they learned.
Other studies have shown that theta activity increases during the retrieval of previously learned material. Still other studies have shown that a brain oscillating in theta mode before exposure to new information is primed to recall that information later on.
Theta Involvement in the Recall of Dreams
Some studies of dream recall, in which participants’ brain waves are recorded as they sleep and they’re awakened periodically and asked to report their dreams, suggest a relationship between dream recall and alpha waves. But the findings in these studies overall are inconsistent–possibly because of different study protocols.
More recent research shows that successful dream recall is associated with both alpha and theta activity in frontal areas of the brain. And, as neuroimaging studies suggest that the mechanisms underlying mental processes are similar during wakefulness and sleep, the researchers propose that it’s the relative presence or absence of theta waves that determines whether or not we remember waking events and dreams.
I don’t know if my shoddy memory is related to a deficit of theta power, or what that may or may not have to do with my predisposition to insomnia. But as long as I’m making a wish list, I’d like a better memory. In addition to more deep sleep, I think I’ll ask for more theta power, too.