Postnatal hippocampal growth in health and prematurity: Modulation and implications

Abstract

The hippocampus is part of the limbic system of the brain, involved with memory and learning functions. The hippocampus is vulnerable to neurological insults during development and is therefore particularly susceptible to damage in preterm (PT) infants. At birth, the hippocampus is about 1.5 cm3 in size and grows up to an average size of about 3 cm3 in the average adult. The right side is larger than the left. The hippocampus grows most rapidly between one and two postnatal months, with continued rapid growth until 2 years of age. The hippocampus resembles adult-like morphology by about 5 years of age, but organization and myelination continue into adolescence. Growth of the hippocampus is mediated by increasing numbers of neurons, dendritic arborization and growth, as well as myelination of axons. Maturation of memory and learning function parallels hippocampal growth and development. Premature birth often results in a smaller hippocampal size, which persists into childhood, adolescence and adulthood. Potential causes for smaller hippocampi in PT populations include stress and postnatal glucocorticoid exposure as well as injury to the white matter. Hippocampal damage may form the basis for learning and memory deficits commonly associated with PT birth. Abnormalities of hippocampal growth and development have also been associated with attention deficit hyperactivity disorder (ADHD), Alzheimer's disease, epilepsy, schizophrenia, bipolar disorder and depression, and therefore early alterations to hippocampal growth may result in a predisposition for other disorders. Hippocampal growth and development is most often studied in vivo using magnetic resonance imaging.