The Infant Brain: A Critical Antecedent of Psychiatric Risk.

Infancy is the time of the most rapid brain development and may be one of the most critical times for psychiatric risk. During infancy, the human brain reaches peak synaptic density ( 1 Huttenlocher P.R. De Courten C. Garey L.J. Van der Loos H. Synaptic development in human cerebral cortex. Int J Neurol. 1982; 16–17: 144-154 PubMed Google Scholar , 2 Huttenlocher P.R. de Courten C. Garey L.J. Van der Loos H. Synaptogenesis in human visual cortex—Evidence for synapse elimination during normal development. Neurosci Lett. 1982; 33: 247-252 Crossref PubMed Scopus (588) Google Scholar ), reflecting intense brain growth driven by dendritic and axonal branch expansion and glial cells promoting myelination—the hallmarks of early connectivity. As these are predominantly immature synapses, this period represents a particularly vulnerable time because ongoing maturation of these connections continues throughout child development ( 3 Huttenlocher P.R. Synaptic density in human frontal cortex - developmental changes and effects of aging. Brain Res. 1979; 163: 195-205 Crossref PubMed Scopus (1892) Google Scholar ). Understanding how the infant brain optimally develops and how adverse exposures alter this development has significant implications for elucidating the mechanisms for the development of psychopathology. Assessment of this development via infant neuroimaging has become a burgeoning area of research with rapid advancements in acquisition, analysis, and predictive modeling. The explosion of this field of research goes beyond how the brain grows within the first years of life to include novel exposures that capture not only the intrauterine environment but also the extrauterine experience from an individual level to systems-level factors. This homage to the infant brain and its progressive processes can be a roadmap for what is known in the field, for emerging advances for inquiry, and for how we can move forward with a focus on risk prevention in early childhood mental health.