Mounting evidence suggests that some babies who succumb to SIDS are born with unseen brain abnormalities. These abnormalities are typically found within a network of neurons that use serotonin as a neurotransmitter and are located in a portion of the brain stem likely to control breathing, heart rate, blood pressure, temperature, and waking from sleep.4
But scientists believe that brain abnormalities alone might not be sufficient to cause SIDS. They theorize that other events also must occur (e.g., lack of oxygen, excessive carbon dioxide intake, overheating, an infection) for an infant to succumb to SIDS (as described in the Triple-Risk Model).
For example, many babies experience a lack of oxygen and excessive carbon -dioxide levels when they have respiratory infections or when they re-breathe exhaled air that has become trapped in bedding as they sleep on their stomachs. Normally, infants sense this inadequate air intake, and their brains trigger them to wake up or trigger their heartbeats or breathing patterns to change or compensate. In a baby with an abnormality in the brain stem, however, these protective mechanisms may be less effective, so the child may succumb to SIDS.
Such a scenario might explain why babies who sleep on their stomachs are more susceptible to SIDS.