Importance of REM Sleep in Developing Infants and Neonates

Overall, sleep and the establishment of regular sleep-wake cycles is vital for infant neurological development. But what about sleep gets the job done? Researchers have shown that REM sleep provides the electrical activity necessary to establish the crucial, long-lasting neural connections that make everything from sensory perception to social skills possible. 

This development of synapses, mentioned on the previous page, functions in the "building of the brain" at the start of neurological development. Scientists believe that the neural firing spikes characteristic of REM sleep in particular play a critical role in the primary establishment of synapses, which affects the development of many crucial neural circuits in sensory/motor and learning/memory systems; and the synapses' lifelong ability to strengthen or weaken their roles in transmission of neural information. 

Sensory and Motor Development

The building of synapses is vital to the development of an infant's touch, proprioception, smell, taste, hearing, vision, emotion, social development, and memory senses, as well as to his or her neural motor, memory, and learning circuits. Allow the following example to illustrate this idea:

Binocular vision, or the brain's ability to combine information from both eyes, occurs in an area of the brain called the lateral geniculate nucleus. The development of visual sensory receptors--eyes--is more straightforward than the development of the neural circuits which process visual information. These neural circuits are helped to develop, researchers think, during the high-activity portion of the sleep cycle known as rapid eye movement sleep. Thus, the ability of individuals to perceive the world by processing information from both eyes may be directly linked to regular REM sleep cycles during prenatal and neonatal development. 

REM sleep is also critical in the development of physical structures underlying sensory neural systems, like the formation of groups of interconnected neurons in the brainstem and sensory cortex, called nuclei, that respond to sensory stimuli and effect appropriate responses.

Researchers posit that brain wave types called pons-geniculo-occipital waves--and their cyclic nature--are responsible for this formation of synapses in sensory/motor systems. Further, each different type of REM sleep wave recorded on an EEG may correspond to the development of a specific sensory system. 

Learning and Memory Development

The process of learning and remembering occurs in three phases. First, an individual creates short-term memory circuits from stimulation by sensory input while he or she is awake and attentive in acquisition. This circuitry is located in the neocortex. In consolidation, short-term memories become long-term memories during slow wave sleep and other forms of non-REM sleep. Information is carried from the neocortex to the hippocampus by theta waves. Lastly, REM sleep facilitates the storage of memories using new neural circuits to organize and transfer memories to appropriate locations in the cortex with different types of theta waves. 

Synaptic Plasticity

REM sleep also appears to play a role in the ability of the synapses set up during development to change over a lifetime, especially with regard to memory. Learning and memory are essentially processes of synaptic strengthening to retain and store information gained every day throughout a lifetime. If the ability to change the properties of a synapse--in addition to the ability to form a synapse at all--is never acquired during development, serious deficits in learning and memory may result. 

Brain plasticity, or "the preservation of the ability to change, adapt, and learn in response to environmental experiences and new needs" (Marks et al.) requires several chemical signals that are all activated during REM sleep in late prenatal and early neonatal stages. Nerve growth factor, brain-derived neurotropic factor, and ubiquinone must be maintained and kept active in neurons to facilitate learning and memory function. These signals activate cAMP-responsive element binding protein (CREB), which alters nerve cell DNA, increasing synthesis of proteins present at synapses that affect long-term memory. 



Interference with Normal Sleep Wake Cycles Affects Development
 
If regular sleep-wake cycles are disrupted or REM sleep is inhibited during prenatal and neonatal development, normal neurological development may be seriously arrested. Experts contend that normal sleep cycles during the period of time between 7 months gestational age (in utero) and 4-5 months post-term are critical for this sensory, motor, learning, and memory development.

Regular, patterned sleep-wake cycles may be delayed if an infant is born prematurely. Current research focuses on the establishment of these cycles as they relate to environmental cues. Activities that come in cycles, such as regular breastfeeding times, may contribute to the establishment of predictable sleep cycles. Interestingly, breast milk contains melatonin and other hormones, which can act as endogenous cues for sleep-wake activity cycles.