Q & A

Ask the expert


Q Why can't we always remember our dreams?

A This has some evolutionary advantage: If we fail to forget dreams, we might confuse

dream experiences with waking experiences, and face possible deadly consequences.

However, occasionally we do remember certain dreams, and some people recall their dreams more often than others.

What are the physiological explanations of such phenomena?


Interrupting a long period of sitting with a few minutes of moderate activity can have short-term benefitson a child's metabolism. While we know getting 30 minutes or more of moderate-intensity exercise each day improves children's health and metabolism, small behavioural changes like taking short walking breaks can also yieldsome benefits.

DR JACK YANOVSKI, United States National Institutes of Health, Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD). He and fellow researchers found that taking three-minute breaks to walk in the middle ofaTV marathon or other sedentary activitycan improve children's blood sugar,compared to sitting continuously. A sedentary lifestyle can put children at risk of developing paediatric obesity and metabolic health problems suchas diabetes.

It has been shown that "high recallers" woke up more frequently at night, and their brains responded to complex sounds (for example, their own first names, compared to simple sounds like beeping) more actively than "low recallers" did during wakefulness.

These findings suggest the possibility of neurophysiological differences between events of successful and unsuccessful dream recall, and between people with high and low dream-recall frequency.

Specifically, scientists have recently discovered in rats that, during rapid-eye-movement (REM) sleep, the memory-consolidating activity decreased significantly.

REM sleep is a phase of sleep where random eye movements and dreaming occur. This finding explains why dreams are so difficult to remember.

•Assistant Professor Hsieh Po-Jang, Neuroscience and Behavioural Disorders Programme, Duke-NUS Graduate Medical School Singapore

•Have a burning science question? E-mail us at STscience@sph.com.sg

A version of this article appeared in the print edition of The Straits Times on August 28, 2015, with the headline 'Ask the expert'. Print Edition | Subscribe