Sustained attention deficits in rats with chronic inflammatory pain.

Attentional deficits are a common clinical manifestation in chronic pain patients. The causes for this impairment are not clear, and explanations range from distraction caused by painful feelings to pain-induced putative alterations of brain regions related to attention processing. However, none of these explanations have been experimentally tested and few studies have addressed this issue in animal models. In this study we compared sustained attention in the 5-choice serial reaction time task (5-CSRTT) in rats before and after chronic pain. Persistent pain was induced by intra-articular injection of Complete Freund's Adjuvant and the development of monoarthritis was accessed by sensitivity to von Frey filaments. Results showed that after the induction of persistent pain, animals presented more errors in accuracy and more omissions in the task trials. When the same animals were studied with two different doses of carprofen (5 and 10mg/kg), the performance was not altered, despite the analgesic effect of the drug. The persistence of attentional impairment during transient analgesia suggests that distraction due to painful stimuli is not the main cause for attentional deficits and that permanent alteration of neurobiological mechanisms of attention should follow chronic pain.