Theta Waves

Theta Waves Photo Credit: clipart.com

A type of spontaneous brain activity seems to create favorable conditions for remembering things.


A pro-memory brain state. I'm Bob Hirshon and this is Science Update.

We've all had the experience of trying to remember something and giving up—only to have it pop into our heads hours or even months later. Now, neuroscientist Charan Ranganath may be onto an explanation. He and his colleagues at the University of California at Davis monitored volunteers' brain activity as they took a memory test. They found that a particular type of brainwave, called theta, set the stage for better recall.

The amount of theta activity you have before you get cued actually predicts whether or not that cue will help remind you of something from the past.

That's in contrast to traditional memory research, which has looked at how different external cues trigger certain kinds of brain activity. This study suggests it also works the other way around: that certain cyclical, spontaneous brain states put us in an ideal frame of mind to remember things. I'm Bob Hirshon, for AAAS, the science society.

Making Sense of the Research

Here's another example of the kind of memory this study explored: You're talking to a friend about movies. You just saw a comedy, and especially enjoyed one actor, whose name was—what was it, anyway? You think really hard and can't for the life of you remember. Then the next morning, while you're brushing your teeth, the actor's name pops into your head. 

There's nothing about brushing your teeth that should have reminded you of the actor's name (unless his last name was Crest or Colgate). On the other hand, thinking hard about the movie, picturing the actor, trying to replay the credits in your head, and having your friend offer up suggestions should definitely have helped—yet they didn't. How can that be?

Most memory studies focus on information you retrieve in circumstances like the conversation with your friend. You learn something (the actor's name, from the credits of the movie), and then later try to retrieve the memory from specific cues or hints. Those cues may come in the form of direct questions ("What was the actor's name?"), indirect questions ("Do you recognize any of the actors in this photo?"), or word associations (words that rhyme with or otherwise remind you of the actor's name). 

This study suggests that there are certain cyclical, spontaneous brain states that are especially conducive to retrieving information. The type of brainwaves involved, called theta waves, intensify and diminish at different times of day, often unpredictably. The researchers didn't try to actually trigger theta waves in the volunteers they studied. Rather, they just monitored them during the recall portion of the memory test to see how high their theta activity happened to be. 

It's important to note that recall improved when volunteers had high theta activity before they heard the cues. If theta activity had increased only after the cues were given, it would suggest that theta waves somehow result from the cues themselves—perhaps a sign of the brain processing memory challenges. That's not what happened here. Subjects whose brains were in a high-theta state already were basically "primed" to do better on the memory test once it started.

High-theta activity clearly isn't the only thing that determines whether or not you remember something. After all, subjects in low-theta states answered some questions correctly, while those in high-theta states still made some mistakes. But the high-theta state was associated with significantly higher recall. Much more work remains to be done, but the study lends support to the idea that everyday memory depends as much on what's going on inside as outside.

Now try and answer these questions:

  1. What are theta waves? How were they associated with memory in this study?
  2. How does this differ from traditional memory studies?
  3. Why was it important for the scientists to measure theta-wave activity before giving the volunteers the memory cues?
  4. If these findings hold up, how might humans someday be able to take advantage of this insight?

You may want to check out the July 1, 2011 Science Update Podcast to hear further information about this Science Update and the other programs for that week. This podcast's topics include: a failing grade for fat substitutes, a master regulator gene for fat, a brainwave that helps control memory, and turning skin cells into brain cells.

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