Are all reinforcers the same? A memory consolidation perspective

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The “memory enhancing” hypothesis of reinforcers generates three testable predictions. First, different reinforcers should strengthen behavior through actions on overlapping neurochemical systems of memory consolidation. Second, because these neurochemical systems overlap, there should be behavioural interactions between different reinforcers. Finally, in the mammalian brain, interacting neurochemical systems converge into a primary “pathway” of memory consolidation. To test these predictions, Sprague-Dawley rats will be trained to associate particular actions (pressing a lever during self-administration) or environmental stimuli (a white chamber during place conditioning), with the delivery of various reinforcers. Following training, the memories of these associations will be measured by assessing the persistence of the learned actions, or the frequency of approach to the environmental stimuli, in the absence of reinforcers. Studies 1-9 will employ pharmacological and neurobiological methods to study systems of memory consolidation engaged by saccharin, fructose, glucose, oxycodone and cocaine. These reinforcers have been selected because, although they have different effects on the body and on the brain, they are all self-administered by rats. The “sweets” will be self-administered intraorally and the drugs intravenously. In Study 10, rats will be trained in a dual self-administration procedure, and behavioural interactions will be characterized during various tests in the presence and absence of one or both reinforcers. Finally, Studies 11-13 will employ neuro-pharmacological methods to explore the interaction between dopamine and noradrenaline; two systems that likely contribute to a pathway of memory consolidation activated by all reinforcing stimuli. This innovative program of research investigates long-standing, basic questions in psychology and neuroscience. There have been no systematic explorations of the neural and behavioral effects produced by different reinforcers in the context of memory consolidation. And, addressing the question of how various reinforcers promote learning, is not only central to the understanding of behavior, but it is also of direct relevance to human health (e.g., obesity and substance dependence).