At What Week Is the Baby Aware in the Womb
When Does Consciousness Arise in Human Babies?
Does sentience appear in the womb, at nativity or during early on babyhood?
MOTHERS will want to crucify me for this seemingly cruel question, but it needs to be posed: How do we know that a newly born and healthy infant is witting? There is no question that the baby is awake. Its eyes are broad open, it wriggles and grimaces, and, most of import, it cries. But all that is not the same every bit existence witting, of experiencing pain, seeing red or smelling Mom's milk.
It is well recognized that infants have no awareness of their own state, emotions and motivations. Fifty-fifty older children who can speak accept very limited insight into their ain actions. Everyone who has raised a boy is familiar with the blank look on your teenager's face when you ask him why he did something particularly rash. A shrug and "I dunno—information technology seemed like a proficient idea at the time" is the most yous'll hear.
Although a newborn lacks self-sensation, the baby processes circuitous visual stimuli and attends to sounds and sights in its world, preferentially looking at faces. The baby'due south visual vigil permits information technology to see only blobs, but the bones thalamo-cortical circuitry necessary to support unproblematic visual and other conscious percepts is in identify. And linguistic capacities in babies are shaped by the environment they grow upwardly in. Exposure to maternal spoken communication sounds in the deadened confines of the womb enables the fetus to pick upward statistical regularities then that the newborn can distinguish its mother's vocalisation and even her language from others. A more complex behavior is fake: if Dad sticks out his natural language and waggles information technology, the infant 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, nowadays-oriented consciousness.
The Road to Awareness
But when does the magical journey of consciousness begin? Consciousness requires a sophisticated network of highly interconnected components, nerve cells. Its physical substrate, the thalamo-cortical complex that provides consciousness with its highly elaborate content, begins to exist in identify 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 place by the third trimester. By this fourth dimension, preterm infants can survive outside the womb under proper medical care. And equally it is so much easier to discover and interact with a preterm babe than with a fetus of the aforementioned gestational age in the womb, the fetus is often considered to be similar a preterm baby, similar an unborn newborn. But this notion disregards the unique uterine environment: suspended in a warm and dark cavern, 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 two slumber states. Chosen active and quiet sleep, these states can exist distinguished using electroencephalography. Their dissimilar EEG signatures go hand in hand with singled-out behaviors: animate, swallowing, licking, and moving the optics but no large-scale body movements in active sleep; no animate, no centre movements and tonic musculus action in quiet sleep. These stages correspond to rapid-centre-movement (REM) and slow-wave sleep common to all mammals. In late gestation the fetus is in 1 of these two sleep states 95 per centum of the time, separated past brief transitions.
What is fascinating is the discovery that the fetus is actively sedated past the low oxygen pressure (equivalent to that at the top of Mount Everest), the warm and cushioned uterine surround and a range of neuroinhibitory and sleep-inducing substances produced by the placenta and the fetus itself: adenosine; ii steroidal anesthetics, allopregnanolone and pregnanolone; one 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 adequately supplied with oxygen. The lamb embryo now moves and breathes continuously. From all this evidence, neonatologists conclude that the fetus is comatose while its brain matures.
Dreamless Sleep?
I complication ensues. When people awaken during REM sleep, they frequently report vivid dreams with extensive narratives. Although consciousness during dreams is not the same as during wakefulness—virtually noticeably insight and cocky-reflection are absent-minded—dreams are consciously experienced and felt. And then does the fetus dream when in REM slumber? This is
not known. But what would information technology dream of?
After nascency, dream content is informed by contempo and more remote memories. Longitudinal studies of dreaming in children by retired American psychologist David Foulkes propose 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 ofttimes static and plain, with no characters that motion or human action, hardly any feelings and no memories. What would dreaming be similar for an organism that spends its fourth dimension suspended in a sort of isolation tank, with no memories, and no style to imagine anything at all? I wager that the fetus experiences null in utero; that it feels the way we practise when nosotros are in a deep, dreamless sleep.
The dramatic events attending commitment past natural (vaginal) means cause the brain to abruptly wake upwardly, withal. The fetus is forced from its paradisic existence in the protected, aqueous and warm womb into a hostile, aerial and common cold world that assaults its senses with utterly strange sounds, smells and sights, a highly stressful event.
Every bit Hugo Lagercrantz, a pediatrician at the Karolinska Institute in Stockholm, discovered two decades ago, a massive surge of norepinephrine—more than powerful than during any skydive or exposed climb the fetus may undertake in its adult life—too as the release from anesthesia and sedation that occurs when the fetus disconnects from the maternal placenta, arouses the infant so that information technology tin can deal with its new circumstances. It draws its first breath, wakes upward and begins to feel life.
Annotation: This article was originally printed with the title, "When Does Consciousness Arise?"
This article was originally published with the championship "Consciousness Redux: When Does Consciousness Ascend?" in SA Listen 20, 5, xx-21 (September 2009)
doi:10.1038/scientificamericanmind0909-xx
(Farther Reading)
- The "Stress" of Being Born. Hugo Lagercrantz and Theodore A. Slotkin in Scientific American, Vol. 254, No. 4, pages 100–107 (92–102); April 1986.
- The Importance of "Sensation" for Agreement 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; November 2005.
- The Emergence of Human Consciousness: From Fetal to Neonatal Life. Hugo Lagercrantz and Jean-Pierre Changeux in Pediatric Research, Vol. 65, No. three, pages 255–260; March 2009.
At What Week Is the Baby Aware in the Womb
Source: https://www.scientificamerican.com/article/when-does-consciousness-arise/