Sleep Needed for Memory

Got kids or grandkids in school? Odds are they are not getting enough sleep, and it is hurting their learning and grades. This is a special problem for older adolescents. At this age, the biological clock shifts and makes them stay up too late if they need to get up at 6-7 A.M. to get ready for school. Kids this age need about 9 hours of sleep a night. So what is the relationship to learning? Two things:

1. When students are drowsy during class, they can't focus attention and will not encode new information effectively. Sometimes they even fall asleep in class, which means they are not encoding anything.

2. Sleep provides an uninterrupted mental environment in which the brain rehearses the events of that day. As documented in dozens of peer-reviewed research reports, this rehearsal promotes consolidation of fragile temporary memory into more permanent form.

Now, two new studies reveal what happens during sleep to accomplish this consolidation task. Just as a computer writes to a hard drive or CD for permanent storage, the brain has to have a storage mechanism. Information in the brain resides, in real time, in the form of nerve impulses flowing around in certain networks. As long as the impulses are present, the memory is present. But if the impulse patterns change, then the information they represented is lost—unless the impulse pattern was played long enough to cause structural change in the corresponding circuitry. Scientists have known for several decades that information is stored in the junctions (synapses) between neurons. We used to think that the synapses involved in learning can grow from repeated use. Impulse patterns representing the day's experiences are replayed during sleep, providing the repetition needed to stimulate growth in the corresponding synapses. But new evidence suggests that learning does not cause the involved synapses to grow, but rather prunes them during sleep to remove irrelevant information.

One of the new studies showed that synapses in mice change structure and chemistry during sleep. In sleep, the synaptic gaps become narrower and the number of neurotransmitter receptors decreases. This may constitute a pruning process. Synapses receive multiple inputs, and a pruning process could help remove irrelevant and interfering information, thus causing a relative magnification of the memory of information being rehearsed during sleep. Another way to think about it is that sleep may provide a mechanism for "smart forgetting."

The second study by another group, also in mice, confirmed this evidence of pruning and further implicated a particular receptor, the one for the excitatory neurotransmitter, glutamate. The investigators even identified the gene that is activated to remove excess glutamate receptors.

The practical application of these findings for school children is that the more they are allowed to sleep, the more time there is for sleep to cause the synaptic changes needed to store the day's learning in the "brain's hard drive." The other, more general, implication of these studies is that the brain's anatomy and physiology are readily changed by experience, a well-established fact that scientists call "neural plasticity."

Readers may be interested in "Memory Medic's" book, Memory Power 101 (Skyhorse) and his more recent book, Mental Biology (Prometheus).

Sources:

de Vivo, Luisa, et al. (2017). Ultrastructural evidence for synaptic scaling across the wake/sleep cycle. Science.  355, 507-510.

Diering, Graham H. et al. (2017). Homerla drives homeostatic scaling-down of excitatory synapses during sleep. Science. 355, 511-515.

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Managing Information to be Remembered

Do you feel embarrassed because you use such memory aids as sticky notes, calendars, shopping lists, designated places for personal items, or other shortcuts to help you remember? If so, don’t feel bad. Some recent research suggests that saving key information in specific ways can be a good idea. Not only do reminder notes, computer files, and other means of information storage make information available for later access, they also can apparently lighten cognitive load and make it easier to remember new information.

Recent experiments tested the hypothesis that saving information is a form of off-loading cognitive workload that frees the brain to be more effective at attending and remembering new information. These experiments by a team at the University of California, Santa Cruz, were inspired by prior work of others revealing that information was not remembered as well if it were saved as a computer file, presumably because participants knew they could look it up later. This finding was subsequently confirmed in other ways. This is the effect of "Memory in the Age of Google," the title of a keynote address I gave to 1,300 teachers at a conference.

But one question not addressed in the prior work was the possibility of an effect on future learning. Now a principle of proactive inhibition of memory formation has been identified in which new learning can be impaired by immediately prior conditions. Could off-loading of previously acquired information affect proactive inhibition? Saving a copy of information might reduce such inhibition by lowering the brain’s workload as it encounters new information to be remembered. Indeed, several groups had established that telling participants they don’t have to remember a list of items enhanced the memory for a second list of items. Thus, it seemed plausible to suggest that saving a list of items, as for example in a computer file, might make it easier to memorize a second list because the learner knows the saved original information can be accessed later.

The test of this idea involved 20 college students who took six trials, each involving study and testing of the contents of two PDF computer files, labeled A and B. For example, they first studied file A, but before being tested on it, they would study and be tested on file B. On half of the trials, participants saved file A after studying it, and the other half were no-save trials in which file A was exited without saving before study and testing on file B. The amount of recall on testing of file B was significantly greater on trials when file A had been saved. This was confirmed in a subsequent trial in which half of the save trials were conducted when participants were told the save procedure was not reliable and that the information in file A could be lost. As long as they trusted that file A was reliably saved, they remembered more from file B.

It seems likely that this principle could apply to other contexts, and thus there might be practical applications. By using a variety of memory saving aids (sticky notes, calendars, etc.), people gain some protection from proactive interference for new learning. And, of course, the earlier saved information is still accessible to be memorized as needed. This may well be the major advantage of taking good lecture notes, for as the learner is off-loading information as it is being saved in the notes, some of the new learning (which is also being saved in the notes) might actually become memory during the note-taking process.

Another obvious benefit is the reduction of anxiety over a concern that you might forget. You know the information is safely stored, so the brain is free to take on new learning without a degree of proactive interference that anxiety always produces. You probably can think better too, as the mind has very limited capacity to hold information in conscious working memory, which holds the information that you think with.

Dr. Klemm is author of Memory Power 101 (Skyhorse), Better Grades, Less Effort (Benecton), and Mental Biology (Prometheus).

Sources:

Sparrow, B. Liu, J., and Wegner, D. M. (2011). Google effects on memory. Cognitive consequences of having information at our fingertips. Science. 333, 776-778.

Storm, B. C., and Stone, S. M. (2014). Saving-enhanced memory: The benefits of saving on the learning and remembering of new information. Psychological Science. Doi: 10.1177/0956797614559285.

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