Primitive reflexes in developing and adult brain - from intellectual disability to dementia

Primitive reflexes are involuntary motor responses elicited by sensory stimuli, playing essential roles in feeding, survival, and protection during the neonatal period. Although primitive reflexes are grounded in central nervous system integrity and are crucial for motor development and sensory processing, they are progressively inhibited and integrated as the frontal cortex matures. The persistence of primitive reflexes beyond 12 months of age may signify underlying neurodevelopmental delays, including intellectual disability, cerebral palsy, autism spectrum disorder, and other related conditions. At the other end of the lifespan spectrum, the reemergence of primitive reflexes or frontal release signs is frequently observed in older patients with various types of dementia, reflecting diffuse cerebral dysfunction and frontal lobe lesions that impair cortical inhibition of brainstem activity. This paper aims to summarize the key clinical implications of persistent primitive reflexes in cognitively affected individuals (such as intellectual disability and dementia) at both ends of the lifespan and to compare their neurobiological bases and prognostic significance to enhance understanding of these phenomena.