In search of the neurobiological underpinnings of the differential outcomes effect.

Correlating unique rewards with to-be-remembered events (the Differential Outcomes Procedure [DOP]) enhances learning and memory performance in a range of species. Recently, we have demonstrated that the DOP can be used to reduce or eliminate the learning and memory impairments associated with animal models of amnesia and dementia. This powerful phenomenon, the Differential Outcomes Effect (DOE), has led to the question: How does such a simple manipulation exert such dramatic influence on learning and memory performance? A revised two-process account of the DOE states that using the DOP results in the activation of reward expectancies through Pavlovian mechanisms. The use of unique reward expectancies alters the nature of cognitive processing used to solve discrimination tasks. The change in cognitive processing is represented by utilization of a different memory system than that commonly used to acquire and remember information when a Nondifferential Outcomes Procedure (NOP) is used. Using neurochemical manipulations, it has been demonstrated that different, potentially independent, brain systems modulate memory performance when subjects are trained with a NOP versus a DOP. This memory-based DOP/NOP distinction resembles other dissociative memory theories in which two psychological processes are purportedly served by distinct neurobiological mechanisms. In addition, such results have important ramifications for the treatment of memory disorders because they demonstrate that stimulus and behavioral manipulations, like drugs, can influence neurotransmitter functioning.