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Baby’s Brain Development

A kiss. A hug. A touch. A leading pediatrician discusses how the benefits of multisensory stimulation affect a baby’s emotional, cognitive, and physical development.

I’m Dr. Paul Horowitz. I’m a general pediatrician in Los Angeles, California. These are my disclosures. And every family that brings a new baby into the world wants what’s best for that child. I mean, they may agonize over which kind of car seat to buy, or which diapers to buy, or what educational program to get for that child. But there’s really something that they can do to improve their child’s cognitive development. There’s something they can do to improve their emotional development, their social development, and their physical growth and development and it doesn’t cost them anything at all. All it is is it requires focus. And it’s multisensory stimulation of that child. I mean, babies thrive on multisensory stimulation and that’s what we’re going to talk about today.

Because what is the natural habitat for a baby? Is it to be pushed around in an infant carrier or held in a car seat with maybe a little toy to – for them to play with? Or is it more for them to be touched and cuddled and tickled and massaged and read to and carried, and get that skin to skin experience. That is the natural habitat for a baby, and that is what’s best for their brains and what will help them with their development. So we’re going to talk about that in the next little while, and thank you for joining me here.

About 2000 years ago, the Roman philosopher, Seneca, came up with this idea that an infant brain is really just a miniature adult brain, that all it needs to do is grow bigger1. Well, over those last 1,000 years – actually over the last hundred years – we’ve come to understand a little bit better that brain development really happens in two general phases.

The first is a prenatal experience, which is really driven by genetics. And it’s – then the second phase is the end of gestation and everything in the first several years of life that is driven by environmental experiences. So the first phase, DNA driven. The second phase, experience driven2. And it got me thinking that it’s sort of like the immune system. I mean, we’re born with some basic immune capability, the so-called innate immune system. But it’s only with experience that the immune system’s adaptive arm, the part that really gets experience from vaccines or exposure to illnesses, that more elegant, more robust immune system that adults benefit from, become smarter and more efficient.3

And the brain is the same way. You’re born with some very basic capabilities, and through experiences, the brain develops. And it gets to a point where you have billions of neurons. So let’s talk about the basic building block of the nervous system and that of course is the neuron, with its dendrites sticking up from the cell body. Then you’ve got the cell body, the long axon along which the signal travels, and then the axon terminals, and at the end of that, you’ve got the synapse across which the signal jumps to the next neuron down the circuit2. The earliest phase of central nervous system development happens at about two weeks gestation. But by about six weeks gestation, you can see cells differentiating into what look to us like neurons. By about two-and-a-half months of gestation, the cerebrum begins to look distinctly human.

And by about five months of age, most of the neurogenesis that’s going to happen has happened and it really looks fairly complete with the exception of the hippocampus, which continues to develop throughout life4. So the general phase is one of neuron differentiation, then there’s this over production, actually you get more neurons, way more neurons than the brain is ever going to need, and then there’s a pruning phase. And it’s during that pruning phase that the brain becomes more efficient, that the circuitry becomes better and more capable and that is seen as what we call cortical thinning, where the brain is becoming a much more efficient organ. Myelination, which is the final stage of neuron development, really doesn’t happen until quite a bit later, and that development continues on such that it’s not until your early 20s that the forebrain, which is responsible for executive functioning, really starts to develop.

And we certainly know from adolescents and what their life experience is like, we can appreciate that myelination doesn’t really happen until your early 20s. So at the end, you have about 10 billion cells per hemisphere. And from 34 weeks on, you get 40,000 new synapses formed per second. And we use the number of neurons and the number of those synapses as a proxy for how the brain is developing. Ultimately, you get somewhere around 10 to the 14th synapses. And although genes can provide the original blueprint for how the brain will be shaped, it can’t possibly control the entire – it can’t possibly guide the entire formation of the final human brain. It’s got to depend on something else and that something else is the environmental experience.

Now in the 1960’s, scientists began to appreciate the influence of deprivation. I mean, sensory deprivation in orphanages were found to result in life-long deficits developmentally. And so efforts were made to not deprive new, young babies and children of sensory input. That evolved into, in the 1980’s, more of a sensory enrichment kind of a culture, where all kinds of programs were developed, all kinds of toys, that were meant to be educational and all kinds of experiences were provided to children, but they tended to be audio/visual. So maybe they were on the television, maybe they were playing music for children in order to help get their brains growing better. What was missing was a multi-sensory approach.

And over the last 20 or 30 years, a body of evidence has built up to support the influence of multisensory stimulation. Because this is a time when you’ve got millions of new synaptic connections being made per second, that the brain is becoming more and more efficient, and multisensory stimulation – that is the concurrent stimulation of multiple sensory inputs to children – is extraordinarily valuable. It’s in those first few years of course, that the neural pathways that support brain development of communication, of understanding, of social development, and emotional wellbeing, really begins to happen and what are rarely travelled pathways of signals going through different parts of the brain become more and more refined5. So a rarely travelled pathway becomes more like a dirt road as more and more signals transport through that pathway. And then that dirt road becomes a paved road, where more and more signaling can go through it, more and more efficiently. And then it becomes more like a super highway of information. And that is the normal and natural development of neural circuitry. So think of it this way. Experience wires the brain; repetition of experiences is what strengthens that wiring. And the developing brain loves repetition. It’s what makes children want to hear the same book again and again. It’s what makes them want to watch the same program again and again. It’s what helps with routining around bedtime, because if it’s a consistent experience, they do much, much better. And everyday routines like that are ideal opportunities to provide that kind of repetitive experience that the baby’s brain thrives on.

And again, it’s that consistent, predictive, repetitive activity that helps the brain develop into what we would say as its maximum potential. So the human brain develops very early on in utero, and very few synaptic connections are made very early on. It’s not until the end of gestation and early in childhood that those synaptic connections are being made. There’s an overproduction, and environment guides, how that circuitry is going to develop.

A baby’s brain creates millions of new connections per second and that multisensory stimulation of hugging, of touching, massaging, skin to skin, carrying, kissing, tickling, these are all the kinds of experiences that will help allow them to get to their maximum potential.

Everyday routines provide opportunities for multisensory stimulation and positive experiences between parents and their children. It’s those everyday moments that otherwise go unnoticed, and you can help me by spreading the word to other families about the importance of these activities.

Thank you.


1. Kolb B, Gibb R. Brain plasticity and behaviour in the developing brain. J Can Acad Child Adolesc Psychiatry. 2011;20(4):265-76.
2. Stiles J, Jernigan TL. The basics of brain development. Neuropsychol Rev. 2010;20(4):327-48.
3. NIH. National Cancer Institute. Adaptive Immunity. Available at: [Accessed on 10 Oct 2022]. 4. Tobin MK, Musaraca K, Disouky A, Shetti A, Bheri A, Honer WG, Kim N, Dawe RJ, Bennett DA, Arfanakis K, Lazarov O. Human Hippocampal Neurogenesis Persists in Aged Adults and Alzheimer's Disease Patients. Cell Stem Cell. 2019;24(6):974-982.e3.
5. Johnson’s Science of the Senses™. Available at: [Accessed on 10 Oct 2022]


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