Slower extinction of responses maintained by intra-cranial self-stimulation (ICSS) in an animal model of attention-deficit/hyperactivity disorder (ADHD)

Children with attention-deficit/hyperactivity disorder (ADHD) show performance deficits and excessive motor activity during extinction and in situations where no reinforcer can be identified, suggesting an extinction deficit in ADHD possibly linked to dopamine dysfunction. The present study examined extinction of responding previously maintained by intra-cranial self-stimulation (ICSS) in spontaneously hypertensive rats (SHR), an animal model of ADHD using three different extinction procedures. Delivery of electrical pulses were terminated altogether or presented independently of responding using two different current intensities. The results showed that more responses were retained in the SHR, especially during the initial transition from ICSS-rnaintained responding to response-independent delivery of electrical pulses with current reduced relative to that given during reinforcement. Slower extinction of previously reinforced behavior is Suggested as an alternative explanation for the frequently observed increased behavioral output that has previously been interpreted as "disinhibition" of behavior in ADHD. (C) 2005 Elsevier B.V. All rights reserved.