Published online at scientificamerican.com on February 6, 2018.
When my son was born a few months ago, he quickly established himself as the tyrant of our household, one that ruled with a singular phonetic ultimatum (“Oooo—whaaah”), tiny iron fists clutched in fury, and a face that roiled like the churning sea. His placid silence instantly devolved to wrath, wrath (once appeased) acquiesced to staring, staring occasionally melted into surprise, an overabundance of which puddled into an outstretched, fearful startle. In his tough, all-work-no-play gig, he presided for weeks without smiling, cooing, giggling or any apparent sign of happiness.
During these overtures, I often wondered why he never cracked a smile. His well fashioned grimace—complete with frown, furrow and squint—proved that his facial muscles were strong enough and coordinated enough to make any number of expressions. In the absence of expressions of happiness, was he unhappy?
I thought on the idea for a while and, in the end, consulted a couple of my neuroscientist colleagues at Yale: Al Kaye, a fourth-year psychiatry resident and Dustin Scheinost, an assistant professor with appointments in the Department of Radiology & Biomedical Imaging and in Yale’s Child Study Center. The three of us have young sons and (I hope) enjoyed the back and forth about whether, during their first weeks, our little men were in fact not happy.
Al, who specializes in mouse calcium imaging (a technique for looking inside the brain at individual neurons’ activity), told a hardline, molecular biology tale that questioned the physical nature of happiness based on the nature of memory. We wondered whether the nature of happiness was being able to call on a pool of memories and, when something reminds you of previous pleasantry, you feel happy and smile. In other words, perhaps a lack of happiness in infants is due to a lack of happy memories. With a wry smile, Al asked, “Well, have you heard about Freud’s concept of infantile amnesia?”
In the late 19th century Sigmund Freud observed that his patients were unable to recall events from early childhood, a phenomenon he called infantile amnesia. Freud thought these patients had repressed troubling, sexual memories from this time (e.g. breast feeding, diaper changing, etc.). Great observation, misguided answer; it turns out that infantile amnesia is found across a wide range of species (including those untroubled by sexual matters) and can be understood in non-sexual, neurobiological terms.
Al told me about a now-famous experiment conducted by Katherine Akers in Paul Frankland’s laboratory at the University of Toronto. The report, published in Science, suggested that memory formation requires a stable network of interconnected neurons, one that, for some types of memories, resides within the brain’s hippocampus. In infants, new neurons are born quite often in a process called neurogenesis. In adults, neurogenesis has slowed and so the overall network structure is more stable.
Akers wondered whether the network instability caused by neurogenesis could explain the infants’ quite poor and the adults’ quite good memories. She tested this idea by inducing neurogenesis in adult mice and discovered that, indeed, they became more forgetful. By slowing neurogenesis in infant mice, she showed that they were more able to remember. It appears that neurogenesis is sufficient to induce infantile amnesia, even in adults!
In order to remember, you need brain neurons to encode and then retrieve memories. In the throes of a neurogenic boom, maybe our little men weren’t happy because they simply couldn’t retrieve happy memories.
Dustin, who specializes in human brain imaging with MRI (a technique that allows large populations of neurons to be studied), told a tale of human brain development. “Being happy requires a fair amount of self-referential thinking, whereas being in pain or being unhappy doesn’t require that in the same way,” he suggested. “To be happy, you have to know that you’re happy. A lot of [our sons’] unhappiness initially isn’t really un-happiness but rather low-level feelings like ‘I’m hungry’ or ‘I’m wet.’ It’s not like ‘oh man, I would be really happy if I weren’t sitting in this wet diaper.’”
This concept of self-referential thinking, or the ability to reflect on how you’re feeling and your desires, is associated with a network of brain regions called the default mode network. Dustin told me about two studies, both published in Proceedings of the National Academy of Science, both of which suggest that the default mode network isn’t fully developed at birth.
The first study, published in 2009, was led by Wei Gao and used a technique called resting-state functional MRI to show that the brain’s default mode network, which is thought to coordinate self-referential thoughts, isn’t fully present at birth but comes more and more “online” with time.
The second study was published in 2010, by Valentina Doria and colleagues. Also using resting-state functional MRI, they showed that the brain networks responsible for sight, touch, hearing and movement were well-formed at birth—which is corroborated by our observations that our sons could see, feel, hear and wiggle at birth (coordination is another story). They also showed that the default mode network was more-or-less present at birth, but that it was still coalescing, still “learning,” such that the activity within this network became more coordinated the older the infants got.
It appeared that both studies showed that the brain’s full repertoire of functional networks were roughed-out at birth, but that they became more polished with age.
Now four months old now, my son has begun to smile and giggle. So it’s more clear when things are going well and when we’re in DEFCON 1. As to the question of whether he’s happy, I remain unsure. Even though he looks contemplatively at his hands (when they’re not in his mouth), I’m unsure this counts as self-referential thought.
Here are some classic works on facial expression:
–The Expression of the Emotions in Man and Animals, by Charles Darwin. Published in 1872, this seminal work provided the first comparison of facial expressions in humans and animals, arguing for a continuity representing an inborn quality to emotions based on environmental demands.
–The Mechanism of Human Facial Expression, by G. B. Duchenne de Boulogne. Originally published in 1862, this work reports Duchenne’s series of experiments wherein he used electrical stimulation to isolate specific facial muscles to understand their contributions to facial expression. The images are worth purchasing the book.
–Emotion in the Human Face, edited by Paul Ekman. A highly accessible textbook explaining the scientific foundations and latest results on the science of human facial expression.