During the baby's passage through the birth canal, the umbilical cord is squeezed, reducing the supply of blood from his mother. The oxygen level in the baby's blood goes down, and the carbon dioxide level rises. When the baby is born, the drop in oxygen makes him take a deep breath, causing his lungs to unfold and fill to full capacity. When the freshly expanded lungs suddenly release their contents, the air rushes through the narrow channel of the larynx and produces the baby's dramatic announcement of his presence, his first cry: "Here I am!"

Babies arrive with a bright-eyed, alert expression, as if they are eager to become acquainted with their new world. This is also the work of the brainstem. When neurons in the brainstem are excited – by loud sounds or strong patterns of light, for example – the neurons produce a sudden surge of norepinephrine, a neurotransmitter that makes the infant more alert and ready for action. Thanks to the baby's breathing, his brain gets five times more oxygen than it had in the womb.

A popular word today is multimedia, but the brainstem has been in that business for a long time. The brainstem receives incoming sensations through separate channels, or "modes." Information from the eyes is in the "visual mode," what a baby hears is in the "auditory mode" and what he feels by touching his skin is in the "somatosensory mode." His brainstem integrates the input from the different channels, a multimodal process.

The brainstem is also "interactive." When a baby hears a sudden loud noise, he startles. The muscles of his whole body jerk in unison. When he sees a face nodding above him, he moves his head and eyes to follow it. His brainstem receives the signals and automatically activates the appropriate muscles.

Content on this site is not a substitute for professional medical or healthcare advice, diagnosis or treatment, and may not be used for such purposes. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical question or condition. Reliance on information presented on this site is at your own risk. This site contains the opinions and views of other users. Given the interactive nature of this site, we cannot endorse, guarantee, or be responsible for the accuracy, efficacy, or veracity of any content generated by our users.