How might delayed development of an impulse-inhibition circuit explain ADHD symptoms?

The symptoms of attention-deficit/hyperactivity disorder (ADHD) may be linked to a delay in the development of the cortical-striatal-thalamic-cortical circuit, a neural loop connecting the prefrontal cortex, basal ganglia, and thalamus.1

This circuit functions as a "braking system" for the brain, responsible for impulse inhibition and the ability to focus on a specific task while resisting extraneous stimuli. When this circuit is underdeveloped, individuals may struggle to filter out these distractions, leading to the characteristic symptoms of inattentiveness, impulsivity, and distractibility.12

Evidence for this developmental lag is supported by observations that ADHD symptoms often subside as individuals age, potentially as the circuit matures—a process that may take until the third decade of life or may not fully occur in some people. This hypothesis aligns with findings that the social development of children with ADHD often mirrors that of their peers but with a delay of two to three years. Furthermore, stimulant medications may help by enhancing the function of this circuit, effectively restoring more typical levels of activity and impulse control.1