(Center for Studies in Behavioural Neurobiology
Montreal, Québec, Canada)
Tuesday 11th October 2011
FIL Seminar Room,
12 Queen Square, London, WC1N 3BG
The neural computation of utility: contributions from the study of brain stimulation reward
Foraging entails repeated decisions about which prey objects to select, how much effort to invest in their pursuit, when to persist, and when to desist. These decisions are based on estimates of returns, costs, and risks. The phenomenon of intracranial self-stimulation has been used to implement a laboratory analog of foraging in which costs, and risks can be controlled precisely, and returns arise from an observable stream of action potentials in an identifiable population of neurons. Although the directly activated neurons responsible for intracranial self-stimulation are largely non-dopaminergic, performance is altered profoundly by changes in dopaminergic neurotransmission. Consensus has yet to be reached concerning the stage(s) of processing at which dopamine neurons intervene and how the influence of these neurons is partitioned between the investment of effort and the evaluation of returns, costs, and risks. I have developed a model linking allocation of behavior to the subjective strength, cost, and likelihood of the rewarding stimulation. Simulations of model output and analysis of empirical data demonstrate that the methods used previously to assess performance for brain stimulation reward produce fundamentally ambiguous results. Using a new measurement method that eliminates this ambiguity, we have reassessed the contribution of dopamine to performance for brain stimulation reward. The model linking behavioral allocation to the subjective strength, cost, and likelihood of reward will be described along with the changes in intracranial self-stimulation produced by cocaine and by the selective dopamine re-uptake inhibitor, GBR-12909. These results will be discussed in terms of the stage(s) of processing at which dopamine influences the pursuit of rewards.