In the comparative psychology lab, we aim to conduct parallel research into decision-making processes in humans and animals. Hereto, we employ behavioral, pharmacological and imaging/recording techniques in humans and rats. Here we give a brief overview of the major methods and paradigms employed in our lab.
Behavioral quantification of decision-making
The study of decision making in humans has a rich tradition stemming from economics, psychology and, more recently, the interdisciplinary field of neuroeconomics. Some studies investigate a change in magnitude, delay, uncertainty, risk or social factors to the subjective perception of value. For example, most people prefer rewards that occur sooner over those that occur later, even if they are somewhat bigger. This can be quantified by determining the discount function of participants: in other words, how much subjective value is lost from a reward as it is delayed in time, becomes more uncertain etc. etc. These subjective discount functions can then become the subject of manipulations of context, or the subject of intercultural comparative studies.
Other studies employ one or more paradigms stemming from Game Theory, such as the well-known Prisoner's Dilemma, the Ultimatum and Dictator Game, and the Trust Game. Briefly, in the Ultimatum and Dictator Game, one player makes an offer on how to split an amount of money or resources, and - depending on the variant, the second player has to accept or can choose to reject the offer. These games probe the concepts of generosity, fairness, social norms and strategic interaction. In the Trust Game and Prisoner's Dilemma, the action of the second player has further consequences for the outcome of player 1, by adding the option to defect, increasing the outcome for player 2 and simultaneously reducing the outcome for player 1. These games investigate the probability that players choose to trust their partners, and whether to reciprocate or abuse this trust.
Imaging of decision-making processes
The advent of neuroeconomics has paired the rigorous investigation of decision parameters with the concurrent measurement of brain activity, mostly using functional magnetic resonance imaging (fMRI). In this way, researchers have uncovered which brain areas are important for (economic) choices. For example, the orbitofrontal cortex and ventral striatum are involved in the computation of reward prediction errors. These errors become apparent when for example a sudden change in the magnitude of the reward associated with a stimulus results in a payout for the subject that is much higher than anticipated on the basis of the learned stimulus-outcome associations. Again, in this way different populations of participants can be contrasted, such as different age groups, or healthy controls and patients, or groups with differing cultural backgrounds.
There is ample evidence that neurotransmitters, such as dopamine and serotonin are involved in decision-making processes, and that natural variation in the levels of these drugs between individuals, or experimental manipulation of these levels has an effect on the participants behavior in decision making tasks. Neuromodulators such as oxytocin or stress-related hormones also have an effect on decision-making. For example, shortly after a stressing event, the levels of the stress hormone cortisol and the neuromodulator noradrenalin are elevated. These substances also reach the brain and have an effect on decision making parameters. Stressed people tend to put a higher value on immediate rewards as compared to non-stressed control participants.
The use of animals in brain research has been of invaluable help in understanding psychiatric illnesses and diseases affecting the brain by providing a model system used to understand what might be going on in the brain when it is in a state of (psychiatric) disease. Poor decision making is also a hallmark of many psychiatric illnesses, such as pathological gambling, addiction and obsessive-compulsive disorder to name but a few, leading to a poor quality of life in these patients. Accurate animal models of decision-making processes are therefore essential in understanding how these deficits might be remedied in patients. Rodents exhibit patterns of behavior strikingly similar to humans in many of the experimental paradigms mentioned above. Coupled with the existing extensive knowledge regarding rat physiology and behavior, these animals can provide an excellent model for understanding (aberrant) decision-making processes
Operant boxes (Skinner boxes) are ideal devices for establishing temporal discounting in rodent models. Among them, probably the most common is the procedure called ‘delay of reward’ (for an example, see Cardinal et al. 2004). In such a procedure two different levers are used, each one associated with a different size of reward. The two available options differ only in the delay and magnitude of the obtained reward. The time between the response and the reinforcer delivery for the delayed reinforcer is then changed across discrete trials. The obtained data are used to generate the so-called indifference curves: when the duration to the large reward becomes (subjectively) too long, the rat will prefer the immediate, small reward. This crossover or indifference point allows the calculation of the rate at which the delayed rewards are discounted or subjectively devalued. In this regard, it was initially proposed that this weakening followed an exponential decay; however, empirical data rather support a hyperbolic (or very similar) discount function.