Signals of energy availability in sleep: consequences of a fat-based metabolism.

Humans can flexibly switch between two primary metabolic modes, usually distinguished by whether substrate supply from glucose can meet energy demands or not. However, it is often overlooked that when glucose use is limited, the remainder of energy needs may still be met more or less effectively with fat and ketone bodies. Hence a fat-based metabolism marked by ketosis is often conflated with starvation and contexts of inadequate energy (including at the cellular level), even when energy itself is in ample supply. Sleep and satiation are regulated by common pathways reflecting energy metabolism. A conceptual analysis that distinguishes signals of inadequate energy in a glucose-dominant metabolism from signals of a fat-based metabolism that may well be energy sufficient allows a reexamination of experimental results in the study of sleep that may shed light on species differences and explain why ketogenic diets have beneficial effects simultaneously in the brain and the periphery. It may also help to distinguish clinically when a failure of a ketogenic diet to resolve symptoms is due to inadequate energy rather than the metabolic state itself.

The therapeutic properties of ketogenic diets, slow-wave sleep, and circadian synchrony.

PURPOSE OF REVIEW: To summarize emerging connections between sleep, ketogenic diets, and health. RECENT FINDINGS: Mechanisms involved in the therapeutic benefits of ketogenic diets continue to be elucidated. Concurrently, the importance of sleep quality and circadian rhythms in their effects on metabolic and cognitive health is increasingly appreciated. Advances in the understanding of the actions of adenosine, nicotinamide adenine dinucleotide, and slow-wave sleep underscore connections between these areas of research. SUMMARY: Many molecular pathways activated during ketogenic diets are known to modulate sleep-wake cycles, circadian rhythms, and sleep stages. Ketogenic diets often have beneficial effects on sleep at the same time as having beneficial effects on particular medical conditions. Enhancement of slow-wave sleep and rejuvenation of circadian programming may be synergistic with or causally involved in the benefits of ketogenic diets.

Fragment memories mark the end of childhood amnesia.

Adults described and dated two kinds of first remembrances: a personal event memory (the recollection of a personal episode that had occurred at some time in some place) and a memory fragment (an isolated memory moment having no event context and remembered, perhaps, as an image, a behavior, or an emotion). First fragment memories were judged to have originated substantially earlier in life than first event memories--approximately 3 1/3 years of age for first fragment memories versus roughly 4 years of age for first event memories. We conclude that the end of childhood amnesia is marked not by our earliest episodic memories, but by the earliest remembered fragments of childhood experiences.