Are fetuses conscious? At 35 weeks, they can process sounds from outside the womb.

May 30, 2021

Babies are are able to respond to different sounds in the womb. Does that make them conscious before birth? (Shutterstock)

A new study on the earliest flickerings of consciousness in humans suggests fetuses may be able to process complex stimuli from outside the womb at 35 weeks of gestation.

A team of researchers that included neuroscientists and medical doctors studied the brain activity of fetuses in 56 expectant mothers from the vicinity of Tübingen, Germany. The mothers were in their late second or third trimester of pregnancy, from 25 to 40 weeks of gestation. Though the researchers were quick to note that the study wasn't able to establish that consciousness is established at 35 weeks, the results showed a distinct pattern in reacting to sound stimuli in the third trimester. 

The study, published May 17 in Developmental Cognitive Neuroscience, opens with a long-debated question: "Can a fetus be conscious?" Lead author and Ph.D. student Julia Moser thinks the answer may be yes, depending on the definition. A larger philosophical debate exists about the term "consciousness" itself, she explained in an interview with The Academic Times. After all, the phenomenon is not black-and-white. 

"Consciousness is not one concept, but really a scale from a little conscious to very conscious," Moser said.

Moser, who completed the current study as part of her dissertation, has long been fascinated by the human mind. During her early psychology research, she learned that studying a child's brain is more challenging because a language barrier inherently exists in children too young to speak. Such children are not able to share their experience with researchers. 

"You can't directly ask young children what they're thinking, as you can with adults. … But you have the possibility to look at what the brain is doing. That really got me excited about developmental neuroscience," she said.

How the brain functions at an early age can have massive impacts on a person later in life. Irregularities in the human brain can affect one's social life, performance in school and behavior, Moser said. 

A better understanding of how neural networks grow and function at very early ages could help researchers detect developmental issues in young children, Moser added. And physicians might be able to design better interventions for neurological problems and other diseases or disorders in newborns when armed with more knowledge about how their brains work.

This isn't Moser's first investigation at the edge of human consciousness: In 2020, she and her colleagues published a paper about rule-learning in newborns. The researchers tested memory traces over time for different sounds and found that newborns' brains responded in a way that could be consistent with basic conscious processing. The next step for Moser and her colleagues was to try and replicate these findings within the womb.

Gestational age was key to designing a successful study in fetuses, explained Moser. "Around week 24 of gestation, the connection we need to process anything we hear appears," she said. Though hearing sounds is possible before this age, a fetus's ears have not matured enough to be connected to the region of the brain responsible for processing noises.

Similar to the previous paper, auditory stimuli were the main variables in the current study. Two tones at 500 Hertz and 750 Hertz were presented to the fetuses at a sound pressure level of 90 decibels. The mother's skin slightly softened the tone, so the scientists estimated that about 60 decibels reached the fetus after the sound traveled through maternal tissue.

The researchers used a noninvasive brain-imaging technique, fetal magnetoencephalography, to measure the neural activity of fetuses. More specifically, they measured the fetuses' response to sounds between 350 and 650 milliseconds after the sounds were played. By changing the order in which the stimuli were presented, the authors could look for variations in cognitive processes that would signify nervous-system activity and therefore sparks of consciousness.

The final dataset contained 81 recordings from the 56 fetuses who were exposed to the lower tone, the higher tone, or both. When comparing the data by age, the researchers noticed a consistent pattern: During the last five weeks of gestation, fetuses appeared to respond to differences in auditory tones. The co-authors' findings align with previous research on fetuses at this age that showed connections in brain regions in charge of consciousness.

One major caveat was the methodology of the study, specifically the auditory pattern, Moser said. She noted that studies on fetuses are inherently more limited than studies on infants or newborns, because the raw data from fetuses is very noisy.

"The more complex your paradigms get, the harder it is to straightforwardly analyze the data and have a neat interpretation," she added. Collecting data from inside a human body makes it harder to pinpoint and isolate a single variable. However, Moser mentioned that knowledge from her previous study on stimuli and conscious processing in newborns made it easier to analyze the results in fetuses.

While the ability to process sound does not equate to the higher awareness we may associate with the term "consciousness," Moser thinks it may challenge widely held beliefs about consciousness and birth. 

"When we say that fetuses are able to process complex auditory sounds, this doesn't make them self-conscious," she said. "[But] a lot of people have the impression that when fetuses are in the womb, they're mostly asleep and are kind of sedated. That's not the case. Before birth, they process a lot of stuff from the environment."

Looking at self-awareness in different animals also challenges commonly held views about consciousness, Moser said. The "mirror test," in which an animal is marked and then exposed to a mirror, to see if they react to that mark and can therefore be said to recognize themselves, exemplifies this: Apes and even some fish can pass the mirror test, suggesting they may be self-aware. 

"Babies are not able to do that, but would you then say that a baby is not conscious? We always think of consciousness as something very human, but I'm not sure if that's quite right," Moser said.

The age-old question of nurture versus nature is Moser's motivation to continue studying how brain networks develop. 

"In early life, all brains look very similar. Then, our environment shapes [our] brains so that we get very individualized — or maybe this is more genetic," she said. "There's a huge gap in knowledge at that early age, which you can nicely study because you don't have much nurture."

The study, "Magnetoencephalographic signatures of conscious processing before birth," published May 17 in Developmental Cognitive Neuroscience, was authored by Julia Moser, Franziska Schleger and Lorenzo Semeia, University of Tübingen; and Magdalene Weiss, Katrin Sippel and Hubert Preissl, University of Tübingen and University Hospital of Tübingen.

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