Sleep and Brain Development: The Critical Role of Sleep in Fetal and Early Neonatal Brain Development

In paper citation (Graven & Browne, 2008)

Note: Human infants are born around 40 gestational weeks.

Normal Sleep in Development

• Sleep & sleep cycles are essential for sensory system development in the fetus and young infant. 
• As early as the end of the first trimester, fetuses begin to show circadian rhythms, periods or rest and activity, and rhythmic hormone production. These circadian rhythms are regulated by the mother's hormones (Rivkees & Hao, 2000)
• Between 20 and 28 weeks' gestation, the human fetus shows irregular and immature brain activity. As the preterm infant approaches 28 weeks' gestation, cell firing becomes regular and starts to occur as synchronous waves. This is organized by the ganglion cell firing. (Lai, et al., 1999).
• By 30 weeks gestation, the EEG patterns of REM and nREM occur, but not continuously. The EEG patterns become continuous between 36 and 38 gestational weeks (Davis, et al., 1999).
• In the fetus and young infant the brain is more active during REM than during wakefulness (Mizhari, et al, 2004).
• At 28 weeks gestation, the sleep cycle is mostly REM sleep. 
• By term at 40 weeks, the sleep cycles are about equal REM and NREM.
• By 8 or 9 months, the sleep cycle is about 80% NREM, 20% REM. This is reflective of adult sleeping patterns (Mizhari, et al., 2004)
• Rapid eye movement deprivation between 30 weeks' gestational age and 4-5 months postterm results in delayed or disordered development. 

Preservation of Brain Plasticity

• 3 cellular components of plasticity:
• nerve growth factor
• BDNF
• ubiquitin
• All three components repond to the stimulation and activation of CREB ( cyclic AMP responsive element binding protein) that regulates gene transcription.

Theory of memory consolidation

• Short term memory circuits in the neocortex.
• Consolidation phase during NREM for novel information.
• Neocortex communicates with hippocampus via theta waves in NREM.
• Hippocampus organizes the information and sends it back to the neocortex using different theta waves in REM. Continued theta waves solidify this memory connection. 
• Stickgold et al., 2008; Yoo, et al., 2007 

Sleep Development in the NICU

• Better sleep organization correlated with improved outcomes in the NICU (Lehtonen & Martin, 2004)
• NICU babies have historically been handled constantly with an average of 100 interventions in 24 hours. 
• NICU babies follow the developmental pattern of their gestational age in terms of sleeping patterns unless they have chronic lung disease (Scher, et al., 1992).
• Kangaroo mother care and breast feeding seem best in establishing sleep-wake patterns in pre-term infants. 

Remaining questions:

What are the established effects of REM deprivation and sleep deprivation?

If SSRIs decrease REM, how does this affect neonatal development? Is there a causal relationship between sleep and cognitive ability or is the correlation deeper?