Heightened motor activity level in male offspring of substance abusing fathers.

Heightened activity level has been implicated in the liability for substance abuse, but no prior research has directly examined motor activity in a sample of prepubertal boys at high-risk for substance abuse. The magnitude of behavioral activity of 10-12 year-old sons of substance abusing fathers (SA +) (n = 42) and controls (SA -) (n = 60) was assessed using a microprocessor-based activity monitor during tasks that demanded significant concentration, effort, and constraint on motor activity, and when no such demands were present. Psychiatric status, measures of temperament traits, and measures of internalizing and externalizing behaviors were also obtained on the boys. Although the groups did not differ during the lower demand task, SA + boys showed significantly greater motor activity than SA - boys during the tasks that required concerted effort, attention, and behavioral suppression. Multiple regression analysis indicated that under the low-demand condition, the presence of an anxiety disorder in the boy was the only significant predictor of activity level. However, under the conditions that demanded effort, concerted attention and behavioral suppression, SA + group membership, and having low rhythmicity (as a temperament trait) predicted heightened activity. Statistically controlling for rhythmicity, the SA + boys were estimated to have about 24% higher activity than control boys. The results suggest that heightened motor activity may be associated with susceptibility to substance abuse.