Do Babies Sleep Most of the Time in the Womb
When Does Consciousness Arise in Man Babies?
Does sentience appear in the womb, at birth or during early childhood?
MOTHERS volition want to excruciate me for this seemingly cruel question, but it needs to exist posed: How do we know that a newly built-in and salubrious infant is conscious? There is no question that the infant is awake. Its eyes are wide open, information technology wriggles and grimaces, and, virtually important, it cries. But all that is not the same as existence witting, of experiencing pain, seeing ruby-red or smelling Mom's milk.
Information technology is well recognized that infants have no awareness of their ain land, emotions and motivations. Fifty-fifty older children who tin can speak have very limited insight into their own deportment. Anybody who has raised a boy is familiar with the blank look on your teenager's face when you enquire him why he did something particularly rash. A shrug and "I dunno—it seemed like a good thought at the time" is the most you'll hear.
Although a newborn lacks self-awareness, the baby processes complex visual stimuli and attends to sounds and sights in its world, preferentially looking at faces. The baby'south visual vigil permits it to run across only blobs, but the basic thalamo-cortical circuitry necessary to support unproblematic visual and other conscious percepts is in place. And linguistic capacities in babies are shaped by the environment they grow up in. Exposure to maternal speech sounds in the muffled confines of the womb enables the fetus to option up statistical regularities so that the newborn tin can distinguish its mother'due south voice and fifty-fifty her language from others. A more than circuitous behavior is simulated: if Dad sticks out his tongue and waggles it, the babe mimics his gesture by combining visual information with proprioceptive feedback from its own movements. It is therefore probable that the baby has some basic level of unreflective, present-oriented consciousness.
The Road to Awareness
But when does the magical journey of consciousness brainstorm? Consciousness requires a sophisticated network of highly interconnected components, nerve cells. Its physical substrate, the thalamo-cortical circuitous that provides consciousness with its highly elaborate content, begins to be in place between the 24th and 28th week of gestation. Roughly two months later synchrony of the electroencephalographic (EEG) rhythm across both cortical hemispheres signals the onset of global neuronal integration. Thus, many of the circuit elements necessary for consciousness are in identify by the tertiary trimester. By this fourth dimension, preterm infants can survive exterior the womb under proper medical care. And as it is so much easier to observe and interact with a preterm baby than with a fetus of the aforementioned gestational historic period in the womb, the fetus is often considered to be like a preterm baby, like an unborn newborn. But this notion disregards the unique uterine surround: suspended in a warm and dark cave, connected to the placenta that pumps blood, nutrients and hormones into its growing body and brain, the fetus is asleep.
Invasive experiments in rat and lamb pups and observational studies using ultrasound and electrical recordings in humans show that the third-trimester fetus is almost always in one of 2 sleep states. Called agile and quiet sleep, these states can be distinguished using electroencephalography. Their different EEG signatures go hand in manus with distinct behaviors: breathing, swallowing, licking, and moving the eyes merely no large-calibration body movements in active sleep; no breathing, no eye movements and tonic muscle action in quiet slumber. These stages correspond to rapid-eye-movement (REM) and slow-wave slumber mutual to all mammals. In tardily gestation the fetus is in one of these two sleep states 95 per centum of the fourth dimension, separated by brief transitions.
What is fascinating is the discovery that the fetus is actively sedated by the depression oxygen pressure level (equivalent to that at the top of Mount Everest), the warm and cushioned uterine environment and a range of neuroinhibitory and sleep-inducing substances produced past the placenta and the fetus itself: adenosine; 2 steroidal anesthetics, allopregnanolone and pregnanolone; i potent hormone, prostaglandin D2; and others. The role of the placenta in maintaining sedation is revealed when the umbilical cord is closed off while keeping the fetus fairly supplied with oxygen. The lamb embryo at present moves and breathes continuously. From all this evidence, neonatologists conclude that the fetus is comatose while its encephalon matures.
Dreamless Sleep?
1 complication ensues. When people awaken during REM slumber, they oftentimes report vivid dreams with extensive narratives. Although consciousness during dreams is not the aforementioned every bit during wakefulness—most noticeably insight and self-reflection are absent-minded—dreams are consciously experienced and felt. And so does the fetus dream when in REM slumber? This is
not known. But what would information technology dream of?
After birth, dream content is informed past recent and more remote memories. Longitudinal studies of dreaming in children by retired American psychologist David Foulkes suggest that dreaming is a gradual cognitive development that is tightly linked to the capacity to imagine things visually and to visuospatial skills. Thus, preschoolers' dreams are often static and plain, with no characters that motility or human action, inappreciably whatsoever feelings and no memories. What would dreaming be like for an organism that spends its time suspended in a sort of isolation tank, with no memories, and no style to imagine anything at all? I wager that the fetus experiences nada in utero; that information technology feels the way we exercise when we are in a deep, dreamless sleep.
The dramatic events attending delivery by natural (vaginal) ways cause the brain to abruptly wake upwardly, however. The fetus is forced from its paradisic being in the protected, aqueous and warm womb into a hostile, aerial and cold world that assaults its senses with utterly foreign sounds, smells and sights, a highly stressful effect.
As Hugo Lagercrantz, a pediatrician at the Karolinska Institute in Stockholm, discovered ii decades ago, a massive surge of norepinephrine—more powerful than during any skydive or exposed climb the fetus may undertake in its developed life—likewise as the release from anesthesia and sedation that occurs when the fetus disconnects from the maternal placenta, arouses the infant so that it can bargain with its new circumstances. It draws its first breath, wakes up and begins to experience life.
Notation: This article was originally printed with the title, "When Does Consciousness Arise?"
This article was originally published with the title "Consciousness Redux: When Does Consciousness Ascend?" in SA Mind 20, 5, 20-21 (September 2009)
doi:10.1038/scientificamericanmind0909-20
(Further Reading)
- The "Stress" of Being Born. Hugo Lagercrantz and Theodore A. Slotkin in Scientific American, Vol. 254, No. iv, pages 100–107 (92–102); April 1986.
- The Importance of "Awareness" for Understanding Fetal Pain. David J. Mellor, Tamara J. Diesch, Alistair J. Gunn and Laura Bennet in Brain Research Reviews, Vol. 49, No. 3, pages 455–471; Nov 2005.
- The Emergence of Human Consciousness: From Fetal to Neonatal Life. Hugo Lagercrantz and Jean-Pierre Changeux in Pediatric Inquiry, Vol. 65, No. three, pages 255–260; March 2009.
Source: https://www.scientificamerican.com/article/when-does-consciousness-arise/
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