Vol. 12, No. 4, 2006 Page 5
Recently, Jeffrey Halperin and colleagues set out to find the answer to a puzzling question: why don't aggressive youths, like their adult counterparts, commonly exhibit low activity of the brain "messenger chemical" serotonin?
In adults, they note, the association between low serotonin function and aggressive behavior is "among the most consistently replicated findings in biological psychiatry, at least in males." Yet only one of several studies has found low serotonin activity in aggressive children, and some studies even report high activity.
To explore this inconsistency, Halperin and colleagues studied 33 boys with disruptive behavior disorders whose serotonin function was originally measured between 1990 and 1994. At the time of the initial study, the researchers categorized the boys—who ranged in age from 7 to 11—as physically aggressive or non-aggressive, after controlling for a variety of potentially confounding factors (age, IQ, reading scores, socioeconomic status, use of medications, race, and attention problems/hyperactivity).
In the initial study, researchers used a test called a fenfluramine challenge to measure serotonin function. Fenfluramine causes an increase in serotonin in the synapses, which in turn causes a rise in plasma prolactin. The magnitude of the prolactin response is considered to reflect overall serotonin function in the hypothalamic-pituitary axis.
At follow-up, the researchers evaluated the boys (now around 15 years of age) using interviews and rating scales that focus on aggression, antisocial behavior, and substance use. Their data, Halperin and colleagues say, show that among youth designated as aggressive during the early study, the magnitude of prolactin response "accounted for 50% of the variance in adolescent aggression and 35% of the variance in adolescent antisocial behavior." No association with substance abuse was seen.
"[I]rrespective of group placement," Halperin and colleagues say, "no child with elevated serotonin function was highly aggressive 7 years later, suggesting that high serotonin may be protective against the development of aggression."
The association between low early serotonin levels and teen aggression occurred only in youths originally classified as aggressive. "Thus," the researchers say, "although low serotonin function is associated with persistence and escalation of aggression and antisocial behavior in aggressive children, it is not sufficient to fully explain the development of aggression."
The researchers point out that fighting is common among young boys but rarely continues or escalates in later life. Noting the relationship between genes and environment (see related article, Crime Times, 2006, Vol. 12, No. 4, Page 6), Halperin and colleagues suggest that while environmental factors may cause increased aggression in early life, "these effects are more transient in those with higher serotonin function."
"Elevated childhood serotonergic function protects against adolescent aggression in disruptive boys," Jeffrey M. Halperin, Jessica H. Kalmar, Kurt P. Schulz, David J. Marks, Vanshdeep Sharma, and Jeffrey H. Newcorn, Journal of the American Academy of Child and Adolescent Psychiatry, Vol. 45, No. 7, July 2006, 833-40. Address: Jeffrey M. Halperin, Psychology Department, Queens College, 65-30 Kissena Blvd., Flushing, NY 11367, Jeffrey.halperin@qc.cuny.edu.