Behavioral Effects of Manipulating Response Effort in an Animal Model of Attention-Deficit/Hyperactivity Disorder

Attention-Deficit/Hyperactivity Disorder (ADHD) is characterized by inattention, hyperactivity and impulsivity, and is a highly heritable behavioral disorder affecting 3-5% of children. Rate, magnitude, quality, and immediacy of reinforcement are important variables that influence behavior. Although less well studied, response effort is an additional variable that affect behavior including choice, stimulus control and response rate, and may affect behavior characteristic of ADHD differently than behavior in typically developing children. Spontaneously hypertensive rats (SHR/NCrl), the best validated animal model of ADHD, display poor stimulus control (inattention), high rates of responses (hyperactivity) and responses with short interresponse times (impulsivity) in operant tasks. Using an operant two-lever visual discrimination task and response effort manipulations, the present study explored effects on stimulus control, response rate and interresponse times in SHR/NCrl and WKY/NHsd controls. Prior to response effort manipulation, stimulus control was lower and rates of responses and short interresponse times were higher in SHR/NCrl relative to WKY/NHsd controls, while increased response effort reduced overall responding in both strains