BECOMING HUMAN focuses research on brain systems, behavior and cognition. For example, attention deficit and hyperactivity disorder (ADHD) Inattention Hyperactivity Impulsivity Diagnosis and treatment requires effective behavior testing. The stop signal task probes people’s ability to control thought and action

“Green light, red light” task. GO GO STOP!

Performance in the stop signal task can be explained by a mathematical model of a race between the process that makes you GO and the process that makes you STOP. This model permits determination of how long it takes to stop, the stop signal reaction time. Kids with ADHD have longer than normal stop signal reaction time.

Time from stimulus (sec) Movements are initiated when certain neurons discharge a certain amount. The variability in time to start moving arises from variability in the time taken by neurons to reach the trigger threshold. How the brain produces movements Activation 0.0 0.1 0.2 Time from stimulus (sec)

Time from stimulus (sec) In the stop signal task, movements are withheld if and only if the movement neurons are prevented from reaching the threshold. Go Stop SSRT Activation 0.0 0.1 0.2 0.3 0.4 Time from stimulus (sec)

Time from movement (sec) Neurons in medial frontal lobe signal errors and success Movement in spite of stop signal = Error Activation Movement when no stop signal = Success -0.2 0.0 0.2 0.4 Time from movement (sec)

Error signals may originate from dopamine neuron input to frontal lobe

A plausible link between genes, brain circuits and behavior Error monitoring signals are based on the activation of dopamine neurons that comprise the brains “reward system” Abnormal dopamine transporter (DAT) linked to ADHD Explore link between DAT and impulsivity by coordinated screening of the DAT gene and performance on the stop signal task Error-related negativity DAT Gene 5p15.3