Primitive Reflexes and Their Role in Nervous System Development

Primitive reflexes (PRs) are foundational components of the human nervous system, and serve as essential building blocks for complex motor and cognitive functions. These automatic, involuntary movements are present at birth and were thought to integrate as the child matures, usually by the age of 8. Controlled by cranial nerves in the brainstem—a primitive part of the brain—these reflexes maintain a balance between the parasympathetic and sympathetic nervous systems to support motor movement, decision-making, and emotional regulation. When PRs remain reactive (retained) or reemerge later in life, they disrupt vagal nerve signals and leave the body in a heightened state of arousal, with higher levels of stress hormones along the HPA axis.