The human brain undergoes dramatic changes during childhood and adolescence. A young person’s brain has a great deal of plasticity, and environmental input can substantially influence how brain regions interconnect. This plasticity explains why a child with a “lazy eye” gains vision when a patch is placed over the good eye. The forced use of the lazy eye leads to new connections in the visual pathways of the brain. If the lazy eye isn’t treated until the child is older, when the visual system is less plastic, the forced use of the weak eye does not cause the same degree of brain re-wiring and the lazy eye doesn’t improve. We will come back to the potential importance of plasticity in young children shortly.
Over the last decade, clinical investigators have found that children as young as 3 to 6 years old can exhibit significant depressive symptoms. Although this “preschool depression” can lead to significant impairment, symptoms often do not meet DSM criteria for major depressive disorder. What happens to these children over time? Does preschool depression predict depression or other behavioral disorders when these children are older?
An important study published recently in the American Journal of Psychiatry by Joan Luby and colleagues addresses this question. These investigators followed a group of nearly 250 3- to 6-year olds recruited from primary care offices and day care centers. At the time of enrollment into the study, 74 children met research criteria for preschool depression. Others had other behavioral disorders, e.g., anxiety disorders, and others were healthy children. Many of the 3- to 6-year olds with depression also fulfilled criteria for other behavioral disorders including ADHD, anxiety disorders, conduct disorder, and oppositional defiant disorder.
As these children reached school age, about 51% of the depressed 3- to 6-year olds met DSM criteria for major depression. This was more than double the rate of depression in children who did not have preschool depression. Thus, depression in a very young child predicts a higher risk for depression when that child reaches school age.
The children with preschool depression also had a higher prevalence of anxiety disorders and ADHD when they reached school age. They did not have a higher prevalence of conduct disorder. Thus, depression in a preschool-aged child predicts substantial risks for one or more of the following when the child is older: major depression, anxiety disorder, and/or ADHD.
Why are these findings important? First, these results raise the strong possibility that some individuals have an onset of major depression dating to very early childhood. Second, as mentioned earlier, the brains of young children are highly responsive to environmental factors. It is possible that therapies directed toward improving parent-child interactions or other behavioral interventions may be effective in treating depression in very young children. Many psychiatric disorders are now thought to involve abnormal function of brain networks that first become manifest in the very young. It is conceivable that early recognition and treatment of symptoms in young children will prevent or reverse the abnormal function associated with such disorders.
Psychiatric disorders in adults are among the most disabling and costly of all illnesses. Further research should help determine whether treating depressive symptoms in young children alters the prevalence and outcomes of psychiatric disorders when these children become adults. Identifying young children at high risk and understanding their progression over time is an important first step in this process. As with all brain disorders, early recognition and early intervention offer the best hope of warding off the devastating consequences of these illnesses.
This column was written by Eugene Rubin MD, PhD and Charles Zorumski MD.