Little Einsteins-In-The-Making: Brain Development in Newborns

The fertility rate in Germany has risen to a 33-year high after years of decline in the rate of births. How will life be for this new generation? How will they percieve the world ? Time to have a look at a newborn's brain!

The emergence of new life, the creation of a little human being, is one of the most fascinating events in this world. Of all organs, the development of the brain is one of the first to start and one of the last to end (although it never really ends). The first structure, the neural tube, forms within the first weeks after conception. The first movements of the fetus can be detected by ultrasound after only 7 weeks and are probably because the first neurons and synapses have already developed in the spinal cord. Although a very basic functional brain is present at birth, many aspects of brain development are nowhere near complete yet.

The Birth of Consciousness
Future parents often wonder how much of the outside world their fetus experiences consciously. For example, is it beneficial to play piano music or speak to the little one in the uterus? Although fetuses can open their eyes after some months, they are mainly asleep and can hardly be woken up. Consciousness is defined as awareness of the body, the self and the outside, and is linked to the condition of being awake. Consequently, the process of birth initiates the development of consciousness by waking the fetus. When a newborn is touched by another person, it reacts differently compared to when it touches itself, indicating it has awareness of its own body.

Sleeping newborn infant with an EEG net.
Fifer, William P., et al. "Newborn infants learn during sleep."  
Proceedings of the National Academy of Sciences 107.22 (2010)

Furthermore, the awareness of smell allows the newborn to pursue the mother's milk. In addition, the ability to discriminate between the mother's voice and that of a stranger develops early on. The effort to reach the mother's breast right after birth also indicates purposeful behavior. Together with other signs such as the sense of pain, language, and short-term memory, newborns fulfil the criteria of basic consciousness and are perfectly equipped to explore the new world [1].

Explosion of Synapses and Glial Cells
Interestingly, the brain of an infant at birth already contains almost the same number of neurons as an adult brain. Now they only have to form their various connections to form mature neuronal circuits. Therefore, an extremely high number of synapses is built during the first months in a process called synaptogenesis, which requires the selection and elimination of synapses. This process, known as pruning, is highly delicate and, therefore, it is not surprising that early life stress can result in the development of behavioral dysfunctions and mental disorders in adulthood [2].

A NEWBORN'S BRAIN 

DEPENDS ON OUTSIDE STIMULI

 

In the past, it was believed that the selection is mainly dependent on the activity of neuronal connections, while the help of glial cells is only required for removing synapses by phagocytosis. However, more recent evidence supports the important role of glial cells in all stages of pruning. A stepwise removal of low-activity synaptic contacts is achieved by a fine-tuned interplay between neurons, astrocytes, microglia and oligodendrocytes that communicate with each other by secreting molecules [3]. For example, during postnatal development, neurons express the chemokine Cc3cl1 (fractalkine) whose receptor is expressed by microglia. As reported first by Paoliceli et al., the lack of this chemokine leads to fewer microglia and delayed synaptic pruning [4].

Sleep, Baby, Sleep…
When one considers the numerous events taking place in the newborn brain – and I've only mentioned a few here – it is not surprising that sleep is absolutely essential for flawless neuronal development. All this learning and processing of environmental stimuli, with their accompanying reorganization of nascent neuronal circuits sounds extremely exhausting for such a fragile organism. Intuitively, one would thus think that the phase of sleep linked to physical rest would be most important for newborns. But quite the contrary. It's actually active sleep, also referred to as rapid eye movement (REM) sleep, which seems crucial for postnatal brain development. Newborns spend about 50% of their sleep in REM (compared to 20% in adults). Indeed, it has been shown that twitching during REM sleep leads to increased activity of Purkinje cells in the cerebellum of rat neonates, indicating that active sleep is important for sensorimotor development [5].

Impact on Our Future Minds
Since the development of a newborn's brain is highly dependent on environmental stimuli, these bewitching creatures should be protected from any harmful influences – beginning already at pregnancy. Everything we experience in our first years after birth will somehow shape our mind for the rest of our lives. This thought is amazing and terrifying at the same time because at that stage these poor little creatures are dependent on how responsible the outside world is …

[1] Langercrantz and Changeaux, Semin Perinatol, 2010
[2] Bock et al., Front Neurosc, 2014
[3] Terni et al., Brain Res Bull, 2016
[4] Paoliceli et al., Science, 2011
[5] Sokoloff et al., Dev Neurobiol, 2014

by Eileen Schormann, PhD Student, AG Krüger

This article was voted "best contribution of the December 2016 issue"