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As each of us goes through life, we remember a little and forget a lot. The stockpile of what we remember contributes greatly to define us a...

New Discoveries on Optimizing Memory Formation

As each of us goes through life, we remember a little and forget a lot. The stockpile of what we remember contributes greatly to define us and our place in the world. Thus, it is important to remember and optimize the processes that make that possible.

People who compete in memory contests (“memory athletes”) have long known the value of associational cues (see my Memory Power 101 book). Neuroscientists have known for a long time about memory consolidation (converting short-term memory to long-term form) and the value of associational cues. But now, important new understanding is arising from a research lab at Northwestern that links cueing to “re-consolidation” and reveals new possibilities for optimizing long-term memory formation.

The underlying research approach is based on such well-established memory principles as:
  1. When information is first acquired, it is tagged for its potential importance or value.
  2. Such tagging is influenced by multiple factors such as repetition, attention, emotion, or purpose.
  3. Valuable memories get preferentially rehearsed, either through conscious will or by covert (implicit) brain processes.
  4. Rehearsal episodes reactive the memory and enhance long-term remembering because each re-consolidation episode builds on prior ones and strengthens the neural circuits that store the memory.
  5. Effectiveness of recall during rehearsal is promoted by use of relevant cues, that is, information that was associated with the original learning material.
  6. Such cues are effective, even when delivered during sleep.

The pioneering study involving sleep learning appears to have been done by John Rudoy and colleagues in 2009 [1}. They showed that people recalled locations of memorized objects better if they heard sounds associated with the locations during their sleep that had been earlier associated with the learning of object locations. The basic finding was replicated in a follow-up study [2].

Most recently, a study by another group also confirmed and extended this concept of using cues during sleep to promote memory formation.The study involved 60 people in their early 20s, screened for good memory ability.[3]All subjects participated in a four-hour learning period beginning in late morning. The learning consisted of 72 images placed in specific locations on a tile-like screen and presented one at a time. As each image appeared a corresponding sound was associated, intended to serve as a learning cue. For example, a dog picture would be associated with barking, cat with meow sound, etc. To create a value bias, each image had a superimposed number representing how important it was to remember this item and its location upon later testing. Subjects were given financial reward for how well they remembered, and thus remembering high-value images was a priority. Half of the images had high value assignments, while the rest had low values.

 Subjects were assigned to four groups:  
  1. Groups 1 and 2 were tested to see how well they could remember where each object had appeared during the learning phase. They then took a 90 min nap while their EEGs were recorded. Half of these subjects heard white noise while the other have was presented the original sound cues of low-value images during non-REM sleep at a level that did not cause awakening. At the end of the nap, recall was again tested.
  2. The procedure in two other groups was similar except that these subjects did not nap. One of these groups watched a movie during the 90 minutes after the learning session, while the other group listed to the low-value sound cues while performing a working memory task.

Not surprisingly, the studies revealed that high-value images were remembered better, irrespective of whether or not a nap was taken. The practical point is that we remember better the things we value and find to have positive reward value. This reminds me of the sage saying that T. Boone Pickens repeated from his basketball coach, who told players after each game: “Don’t dwell on your mistakes. Think about what you did right and do more of that!”

In the study, half of the low-value associations were rescued by cueing during wakefulness and all of them were rescued by cueing during sleep, even though only half of the images were cued. Notably, the best effects occurred during the deepest stage of sleep. No explanation was given to explain the sleep benefit, but I suspect it is because the sleeping brain is not distracting itself with irrelevant thoughts. This is consistent with the finding that low-value memories were not rescued well during REM sleep, when the brain is busily engaged in dreaming. The REM-sleep finding is at variance with other studies that reported a memory consolidating benefit of REM sleep. Apparently, the test conditions make a difference and more research is needed here.

Low-value associations were preferentially forgotten in the group that was not allowed to nap. This likely signifies that a brain busily engaged with other thoughts is less able to selectively consolidate memories, and only high-value items are likely to survive. This accords with the long-held theory that distractions and multi-tasking interfere with memory consolidation.

In summary, memory optimization would seem to require one to:

1.    Create associations that can serve as memory cues.
2.    Place a high value on the cues and their targets.
3.    Repeatedly present the cues and replay the initial information. When awake, present the cues in self-test mode. When asleep, even better results would obtain if cues were presented at a level that does not cause awakening during the early night sleep when sleep is deepest and there is little dreaming.

1. Rudoy, J. D., Voss, J. L., Westerberg, C. E., Paller, K. A. (2009). Strengthening individual memories by reactivating them during sleep. Science. 326: 1079.

2.. Antony, J. W, Gobel, E. W., O’Hare, J., K., Reber, P. J., and Paller, K. A. (2012). Cued memory reactivation during sleep influences skill learning. Nat. Neurosci. 15: 1114:1116.

2. Oudiette, D., Antony, J. W., Creery, J. D., and Paller, K. A. (2013) The role of memory reactivation during wakefulness and sleep in determining which memories endure. J. Neurosci. 33(15): 6672-6678.

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