Isegoria

The remarkable memory-boosting benefits of undisturbed rest were first documented in 1900 by the German psychologist Georg Elias Muller and his student Alfons Pilzecker:

In one of their many experiments on memory consolidation, Muller and Pilzecker first asked their participants to learn a list of meaningless syllables. Following a short study period, half the group were immediately given a second list to learn — while the rest were given a six-minute break before continuing.

When tested one-and-a-half-hours later, the two groups showed strikingly different patterns of recall. The participants given the break remembered nearly 50% of their list, compared to an average of 28% for the group who had been given no time to recharge their mental batteries. The finding suggested that our memory for new information is especially fragile just after it has first been encoded, making it more susceptible to interference from new information.

Although a handful of other psychologists occasionally returned to the finding, it was only in the early 2000s that the broader implications of it started to become known, with a pioneering study by Sergio Della Sala at the University of Edinburgh and Nelson Cowan at the University of Missouri.

The team was interested in discovering whether reduced interference might improve the memories of people who had suffered a neurological injury, such as a stroke. Using a similar set-up to Muller and Pilzecker’s original study, they presented their participants with lists of 15 words and tested them 10 minutes later. In some trials, the participants remained busy with some standard cognitive tests; in others, they were asked to lie in a darkened room and avoid falling asleep.

The impact of the small intervention was more profound than anyone might have believed. Although the two most severely amnesic patients showed no benefit, the others tripled the number of words they could remember — from 14% to 49%, placing them almost within the range of healthy people with no neurological damage.

The next results were even more impressive. The participants were asked to listen to some stories and answer questions an hour later. Without the chance to rest, they could recall just 7% of the facts in the story; with the rest, this jumped to 79% — an astronomical 11-fold increase in the information they retained. The researchers also found a similar, though less pronounced, benefit for healthy participants in each case, boosting recall between 10 and 30%.

Della Sala and Cowan’s former student, Michaela Dewar at Heriot-Watt University, has now led several follow-up studies, replicating the finding in many different contexts. In healthy participants, they have found that these short periods of rest can also improve our spatial memories, for instance — helping participants to recall the location of different landmarks in a virtual reality environment. Crucially, this advantage lingers a week after the original learning task, and it seems to benefit young and old people alike. And besides the stroke survivors, they have also found similar benefits for people in the earlier, milder stages of Alzheimer’s disease.

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