Trial lecture title: Construct validity in animal models of ADHD: The role of dopamine in attention and impulsive choice.
Th ordinary opponents are:
- First opponent: Professor Mark Reilly, Central Michigan University, USA
- Second opponent: Professor Göran Söderlund, Western Norway University of Applied Sciences
- Leader of the committee: Associate Professor Torunn Lian, Oslo Metropolitan University
The leader of the public defence is Professor Ingunn Sandaker, Oslo Metropolitan University.
The main supervisor is Associate professor Espen Borgå Johansen, Oslo Metropolitan University. The co-supervisor is Professor Per Holth, Oslo Metropolitan University.
Thesis abstract
An animal model represents a human target group in one respect or another, with the aim to gain new knowledge about human conditions. The Spontaneously Hypertensive Rat (SHR) is an animal model of Attention-Deficit/Hyperactivity Disorder (ADHD).
A characteristic of ADHD is impulsive behaviour, commonly measured using the delay discounting task. This involves choosing between a small, immediate reinforcer and a large, delayed reinforcer, and people with ADHD tend to choose the smaller reinforcer more often than controls.
This thesis aims to outline, test, and improve upon the methodology used when testing animals on the delay discounting task.
Study 1
In Study 1, researchers are cautioned that knowledge gained from animal models does not immediately apply to humans without supportive follow-up testing.
The paper also recommends the use of mechanistic validity, which is the degree to which the cause of a behaviour is the same in both humans and animal models.
Study 2
Study 2 argues that it is not productive to investigate whether impulsive choice is really a reflection of sub-optimal reward-maximizing behaviour, because what signifies an optimal choice is dependent on too many variables.
The paper also advocates the use of a preference test preceding the delay discounting experiment. This test documents, rather than assumes, that the animals prefer the large reinforcer in the absence of response-reinforcer delays.
Study 3
Study 3 was an experiment with the SHR model, investigating the effect of learning history on impulsive choice.
It was found that rats that previously chose the large reinforcer in the absence of delays did not immediately become impulsive when exposed to long response-reinforcer delays. Once impulsive behaviour manifested it was never extinguished, even when delays were removed.
Study 4
Study 4 evaluated the effect of the inter-trial interval and trial length in delay discounting. Delay aversion theory proposed that people with ADHD choose the small reinforcer in order to reduce trial length.
In animals, this phenomenon is only assumed, not observed. Results from Study 4 clearly show that the length of the inter-trial interval, and by extension trial length, does not affect an animal’s performance on delay discounting, even if its length is signalled by an audio cue.
Studies challenge the validity of ADHD theories
Taken together, these studies challenge the validity of ADHD theories and their ability to explain impulsive choice.
The thesis also recommend animal model researchers to carefully document behaviour rather than assuming the effects of various variables, aiming to promote more rigorous animal model experimentation in impulsive research.
