Declining Blood Glucose Levels after a Cognitively Demanding Task Predict Subsequent Memory

There is a series of reports that failing levels of blood glucose are associated with enhanced cognitive functioning. The hypothesis was examined that declining blood glucose levels are associated with enhanced memory only when individuals are subjected to cognitive demand. Subjects consumed either a placebo or a glucose containing drink, and then either sat quietly for 20 min, or performed a vigilance task. All subjects then attempted to recall a list of words. In those who performed the vigilance task, and consumed a glucose drink, memory was better when blood glucose levels fell more markedly. Those whose blood glucose levels fell more markedly also produced fewer errors while performing the vigilance task. In no instance did a fall in blood glucose predict the memory of those who had not performed the demanding vigilance test.