On Consolidating Memories During Sleep

Sleep helps us to build memory toward a robust state termed consolidation. Very soon after birth, the healthy term newborn soon enters an alert cycle that may last 1 to 5 hours (2 to 2 1/2 hours is average), and this early alert cycle is an ideal time for the youngest newborn to practice learning milk-feeding skills at the breast. Following this earliest feeding session, newborns enter a sleepy cycle of satiety and in recovery from birth. When a newborn has learned the oral grasp (or latch) in the initial alert cycle after birth, then awakens after a period of sleep, the infant's subsequent feeding movements for the oral grasp are expected to becoming increasingly more smooth and accurate (and therefore faster) at subsequent feedings when practice is specific to the task.  (An exception to the infant's display of increasing speed and accuracy for the oral grasp at the breast is during pronounced breast engorgement, which can serve as a temporary learning constraint for the infant.)  

Newborns must feed often in order to thrive, and with more task-specific feeding practice, motor memory for feeding becomes even more robust. This strengthened motor memory is reflected in the baby's increasingly greater performance of the oral grasp (the young novice soon becomes The Insta-Latch Baby), and the infant also becomes more skilled in milk transfer, so that greater volumes of milk can be transferred over increasingly shorter periods of time. Interestingly, as newborns become gradually more skilled in a milk-feeding method, gradually less sleep is required. 
                                                                                                                                          However, early memories are often fragile. Consider the fragile memory for a new computer password or a new telephone number, where the repetition of practice is necessary for building robust memory for that information.

In motor learning, such fragility can be frequently observed during the formation of early motor memories for infant feeding when a breastfed infant is given a learning experience with an artificial nipple, and particularly (but not only) if the introduction to an artificial nipple occurs during early skill acquisition at the breast, i.e., during early motor learning toward motor control.  If the infant's learning experience at the breast is followed by a learning experience with an artificial nipple, the infant's subsequent return to the nipple-areolar complex is often observed as decreased speed and accuracy (skill decay) for the oral grasp.

Following a learning experience with an artificial nipple, there are often many pronounced observations of a delayed and/or prolonged reaction time (RT) for the infant's oral grasp of the nipple-areolar complex (delayed onset of rooting and/or prolonged rooting for sensory processing, which includes but is not limited to texture and shape discrimination as well as target identification, followed by action planning); as well as a prolonged movement time (MT) for the oral grasp and/or effective suckling, resulting in a prolonged response time.  A significant inhibition of return (IOR) is also frequently observed -- the delay in responding to the previously cued (or orienting) stimulus. Although a wealth of longitudinal studies have correlated artificial infant feeding methods and artificial infant milks with both shorter duration of exclusive breastfeeding as well as early termination of the entire breastfeeding course, the universal phenomenon of infant breastfeeding difficulties that often follow the use of an artificial nipple can also be formally studied by using these real-time measurement parameters toward greater understanding of the infant’s skill acquisition for milk-feeding skills.

Among exclusively bottle-fed populations, routine task-switching between different styles of artificial nipples is never the norm in hospital settings or among families, although such task-switching of various styles of artificial nipples and subsequent switch costs of decreased speed and accuracy for the oral grasp and/or effective sucking can be studied in bottle-feeding infants as well. Skill acquisition in bottle-feeding populations can also be studied when bottle-fed infants learn their feeding skills unimpeded by task-switching to different styles of artificial nipples. The impact of sleep can also be studied among exclusively bottle-fed infants during their acquisition of bottle-feeding skills, regardless of whether the bottled milk is mother's milk, human donor milk, and/or artificial infant milk.

Motor learning is a complex process, and the presence of the primitive survival reflexes hastens the newborn's acquisition of milk-feeding skills in dramatic support of the newborn's survival. However, the newborn's reflexive movements are often more heavily weighted toward the more recently learned milk-feeding method (a recency effect), rather than equally weighted reflexive feeding movements for all infant milk-feeding methods all the time. 
                                                                                                                                        When the repetition of practice is specific to the task, the infant has the opportunity to build increasingly greater motor control during the process of motor learning for milk-feeding skills. The brain continues to process and strengthen motor memories between practice sessions, and this critical processing also takes place during sleep.

As the spring semester winds down on college campuses, parents are likely to advise their college-aged students not to stay up all night cramming for final exams, but to study as much as possible throughout the semester and to get adequate sleep, including during the week of final exams. When the repetition of frequent studying (in-session learning) is followed by regular study breaks and adequate sleep (between-session learning), this academic routine is expected to result in more robust memory for students everywhere. In studies on the impact of sleep in the aging population, adequate sleep is one of many important factors in supporting and optimizing cognitive function.

A new review article on daytime napping in infants and children from the journal, Nature and Science of Sleephttps://www.ncbi.nlm.nih.gov/pubmed/22430027