Imagine a scientist sitting you in a device that can detect changes in your brain activity and then plays a cycle of sounds. Over and over again, three low tones are heard, followed by a high one. Then you hear something different: four low tones in a row. The scientist does not have to ask you if you were aware of the change. This is because our brains normally respond to a strange sound with a brief, distinctive flash. That flash turns out to be a surprisingly reliable marker of consciousness: that complex and mysterious state of being aware of one’s thoughts and one’s existence in the world, which may also be present to some extent in other animals. People in a coma do not produce this beeping sound when they hear strange sounds. Neither do people who are asleep. Let’s now imagine that the parents of a newborn take their baby to the same laboratory to perform the same test. The tones play. Will there be a problem? Is that squirming, gurgling baby conscious? As humans, they are potentially conscious; we know that. But right now, with their semi-developed brains and cognitive limitations (they can’t yet speak, focus their eyes, respond to instructions), they don’t seem to be conscious, at least not in the way that adults are. In fact, there is an active scientific debate about whether newborns possess consciousness. Solving it could help solve one of science’s most enduring mysteries: what consciousness is, how it arises, and how we can tell if another being possesses it. Ask any researcher who studies consciousness, and they will probably have a rough but useful definition. “Consciousness is a process of being receptive to the outside world and mixing it with our own internal world, to create a sense of who we are and where we are,” said Dr. Topun Austin, a neonatologist at the University of Cambridge. But Dr. Austin is well aware that this definition does not speak to how that process develops: where in the brain awareness of the activity of neurons arises, or how their symphony of signals creates that sense of being ourselves in the world. Scientists have developed many detailed theories to address those questions. But there is little agreement on what is right and no solution in sight. “There is no consensus that we all agree on,” said Joel Frohlich, a cognitive neuroscientist at the University of Tübingen in Germany. The stakes have only increased in recent years. Researchers have implanted millions of functional human brain cells into mice, for example, prompting speculation that the work could one day endow mice with consciousness. Philosophers and theologians are pondering whether AI will become conscious and how we can know for sure. Amid all the uncertainty, there is one fact that everyone can agree on. In each of our lives, there was a time when our brains were still too rudimentary to support consciousness, and there was a time when that changed. Even if we can’t tell when babies become conscious, Dr. Austin said, “one thing we can be sure of is that they will become conscious again.” In recent years, Dr. Austin and other researchers have focused on that transition. They are using new types of brain scanning technology to study babies’ brains like never before, giving babies not only intermittent tests, but even investigating what babies experience before they are born. By determining when consciousness fully flourishes, perhaps they can improve our understanding of how it works and what it does in all of us. “I really see it as a frontier area in consciousness science,” Dr. Frohlich said. By the time his first son, William, was born, Darwin had come to embrace the idea of evolution: the human mind, endowed with consciousness, had evolved over many generations from simpler instincts. Darwin also believed that all children followed a similar path in their first years of life, as their brains developed from simple structures to complex thought vessels. And so, beginning with William and continuing with his later children, he took careful notes on how young humans changed during the first months of life. Early on, Darwin recorded “instinctive actions” such as “sneezing, hiccups, yawning, stretching, and, of course, sucking and screaming.” Only when her children grew up did any mention of sophisticated behavior begin to appear in her notebook: her children learned to recognize themselves in mirrors, to speak simple words, to reach for objects. Before that, he declared: “There are no traces of consciousness in very young children.” Darwin was not an outlier in this belief. Doctors of the time also assumed that babies were not conscious, and that assumption shaped their care for generations. During newborn surgery, for example, it was common not to use anesthesia; drugs could damage a young brain; If the babies were not conscious, what was the value of rendering them unconscious? As recently as the 1980s, doctors routinely withheld anesthesia for newborns, seeing no benefits that could outweigh the risks. Doctors have since reversed this practice, as the study of babies has matured. More recent research has found, for example, that newborns process pain signals in many regions of the brain, suggesting that their experience is similar to that of older children and adults. Other studies have found signs that babies are capable of surprisingly complex ways of thinking long before they can speak. They can recognize that a face is more than the sum of its parts; They can perform simple forms of mathematics in their heads. Findings like these caused scientists to reconsider Darwin’s conclusion; perhaps consciousness arises earlier than previously believed. To explore that possibility, researchers have borrowed some of the methods used to measure consciousness in adults, such as playing those strange sounds. In an experiment conducted in Germany, scientists placed newborns in a special crib equipped with sensors that could detect small magnetic fluctuations and then equipped the babies with headphones. When the researchers played combinations of low and high tones, the babies’ brains produced different beeps in response. “This shows that the newborn brain is already functioning very close to what we find in an adult brain,” said Claudia Passos-Ferreira, a philosopher at New York University. But Dr. Passos-Ferreira and other researchers don’t consider that finding conclusive. Some experiments have failed to find other markers of consciousness in babies. That’s why researchers are doing many different tests, perhaps to identify a group of markers of consciousness. “If we see a lot of markers appearing at the same time, that’s very suggestive that that’s when consciousness begins,” Dr. Frohlich said. Some of the most promising recent results come from a major effort in London called the Developing Connectome Project. To do this, the scientists had to modify a functional MRI device. Typically, adult subjects lie on a table that slides inside a large cylinder. Instead, engineers built a small cradle with a plastic cap on one end to detect activity in a baby’s brain. The project team performed brain scans on hundreds of babies, including newborns. They drew maps of children’s brains and recorded the electrical activity that arose spontaneously during the 15-minute scans. Lorina Naci, a neuroscientist at Trinity College Dublin, and her colleagues have been busy analyzing those recordings. A distinctive feature of consciousness in adults is the way in which different parts of the brain are activated in a coordinated manner. Those connections can evaporate when adults sleep or are under anesthesia. In recent studies, Dr. Naci’s team has found that regions of babies’ brains activate together in networks similar to those of awake adults, offering another early marker of consciousness. Meanwhile, new technology is speeding up data collection: Instead of subjecting babies to scans, researchers can put caps on their heads that monitor the brain with ultrasound or light. birth.Dr. Naci and his colleagues have found that some babies born prematurely also show networks of active brain regions that hint at conscious experiences. Dr. Frohlich and his colleague are studying fetuses still in the womb, having pregnant volunteers rest their bellies on a device that can detect the weak magnetic fields produced by the fetal brain. For now, consciousness before birth is an even greater mystery than consciousness in newborns. Scientists generally agree that consciousness cannot arise before the fetal brain has matured enough to receive signals from the senses and then integrate them into a unified experience. Before 26 weeks of gestation, these neuronal connections do not exist. Scientists can only guess how soon afterward these connections develop. In a survey of experts conducted by Dr. Passos-Ferreira, the majority estimated that babies have some consciousness when they are born. “There are still some skeptics about childhood consciousness who think it emerges later,” Dr. Passos-Ferreira said. “It’s a minority, but they’re still there.” As scientists map the birth of consciousness, they hope to gain a better understanding of how it evolved in humans in the first place. For children and adults, awareness is vital to communicating through language and carrying out complex forms of thinking. But if babies turn out to be conscious at birth, and long before they can speak or make plans for the future, then it must serve some additional purposes. Perhaps, Dr. Naci said, awareness allows babies to start making sense of the world as soon as they enter it, “to help them start functioning in terms of learning and development as soon as they are born.” But, he added, understanding consciousness in babies may require a change in the way we normally think about consciousness in general. By counting all the ways a baby’s brain regions interact with each other from second to second, Dr. Naci and her colleagues have discovered that the baby’s brain actually shows more complexity than that of an awake adult. We tend to think of consciousness along a single line, on a gradient from unconscious to fully conscious. It is the path we travel every day when we wake up and sleep. But what if consciousness had more dimensions, more ways of being?Dr. Naci speculates that babies may be conscious at birth, but in a way perhaps more open to the world. “The idea is that they have this ability to perceive more of the environment in much richer and more diverse ways,” he said. “They might have a very different experience than we have as adults.”
