Is Polydipsia a Predictor of Cognitive Impulsivity?

Abstract

Two nonhuman animal models of Attention Deficit/Hyperactivity Disorder (ADHD), the Spontaneously Hypertensive rat (SHR) and Lewis (LEW) rats, were used to explore the possibility that schedule-induced polydipsia is a predictor of cognitive impulsivity. A concurrent-chains procedure consisting of 60 choice cycles was used. Each cycle began with one response on the back lever causing two front levers to extend into the experimental chamber. Choice was measured in the initial link with the levers using Random Interval schedules arranging entries to two terminal links. In one terminal link, the left lever produced one food pellet immediately (SSF). In the other terminal link, the right lever produced 4 food pellets (LLF) after a delay of 0.1, 5, 10, 20, 40 or 80 seconds. A bottle of water could be available (B), or could not be (A) available, to the rats in the choice situation according to an ABABA design. The results showed that the rats discounted the value of the LLF as a function of the delay to deliver it. Both strains of rats drank water during the one-minute blackout following 10 choice cycles during the session. But the SHRs drank more water than the LEWs, especially during the delays to the LLF. A negative correlation between polydipsia and discounting rate suggests that: (1) polydipsia is not a predictor of impulsive choice, and (2) polydipsia is not related to motor impulsivity.