Understanding the complexity of the brain and nervous system is something that researchers have focused on for generations. One area of focus is that of developmental neurobiology, or the study of the development of the brain and its various processes. Research can be limited to the embryonic development of the brain and central nervous system, or it can focus on later physical development; some researchers focus on the physical development itself while others emphasize the role the development of the central nervous system plays in a person's overall health. Because there are a host of illnesses that can plague the various components of the central nervous system, understanding the development of these elements can enable physicians to either address the issues before they manifest or craft more precise treatment methods that resolve the underlying problems.
This particular field of study often combines research from various professional fields, including both neuroscience and developmental biology. Because the body changes dramatically throughout the course of one's life, understanding how neural development is different based on age and developmental level is key to understanding any present symptoms. Developmental neurobiology also focuses on the wide array of impairments that can occur at any stage of development, whether sensory, motor, or cognitive in nature. Rare diseases that are linked to the central nervous system are another area great research in developmental neurobiology, with the focus of researchers often being just to understand the given illness and its corresponding physical effects more.
A common disorder of individuals with developmental neurological problems is PDD. Pervasive Developmental Disorder (PDD) is a group of disorders that includes the following:
- Rett disorder
- Childhood disintegrative disorder
- Asperger syndrome
- Pervasive developmental disorder-not otherwise specified (PDD-NOS).
The prevalence of these disorders has increased over the last four decades from 4.4 cases per 10,000 to modern estimates of over 12.1 cases per 10,000.Although the underlying causes are unclear, research has suggested a genetic link involving variations in certain genes expressed within the brain, the serotonin transporter gene and other genes for serotonin receptors, and a specific type of mutation on the maternally-inherited chromosome 15q. Neurobiological studies confirm differences in brain composition of individuals with PDD, the most notable of which is an increased brain size by as much as 10%.This increased size reflects increases in the amounts of cerebral and cerebellar gray and white matter. These differences may be responsible in part for the behaviors exhibited by PDD individuals, including impaired social interaction and communication abilities. A variety of therapies exist to treat these disorders, including Applied Behavioral Analysis and others aimed at addressing cognitive, emotional, and language deficiencies.
Children diagnosed with PDD exhibit a number of common neurobiological characteristics. First, while the head circumference at birth appears normal, by the age of three to four years, the brain size of children with neurobiological developmental problems is approximately 10% than that of unafflicted children. This enlargement of the brain is evident in the cerebral gray and white matter as well as in the cerebellar gray and white matter. Due to the increase in brain size, researchers expected to see an increase in the number of markers within the brain that would be indicative of greater neuron or synapse density. However, the opposite was found to be true. This may be due to changes in the numbers and sizes of neurons; elaboration in axons, dendrites, or synapses; death of neuronal cells; or myelination. Inflammation has also been observed in these brain regions. Post-mortem studies of the brains of individuals with PDD revealed decreases in the number of certain brain cells and changes in size and density of certain neurons.