Recently, much attention has been focused on the psychopharmacology of WM. Two main developments have converged to create this interest. First, there have been significant advances in our understanding of the anatomy and organization of the neurotransmitter pathways in the mammalian brain. These pathways include the major monoaminergic (dopamine, serotonin and norepi-nephrine) and cholinergic projections, which innervate diverse forebrain regions that have discrete psychological functions. This has refined our understanding of the neurochemical basis of pathophysiological conditions such as ► Parkinson's disease, ► Alzheimer's disease, and ► schizophrenia, which are characterized by memory loss and cognitive disorganization. Second, research has linked poor psychosocial functioning to persistent cognitive deficits, including WM, which fail to improve with current pharmacotherapies. Consequently, there has been an important need to identify pharmacological compounds intended to improve cognitive deficits in psychiatric illness and dementia (see ► cognitive enhancers), and WM impairments have become important targets for treatment.
In animals, WM is assessed using the spatial delayed response task, which evaluates the animal's capacity to act on the basis of stored information rather than information available in the environment. Typically, a monkey is shown the location of a food morsel. The food morsel is then hidden from view. After a delay of several seconds, the monkey is required to choose one of the two locations. To be rewarded, the animal must remember where the food was located prior to the delay period. In a variation of the task, ► spatial delayed alternation, the monkey is required to alternate between left and right food wells in successive trials that are separated by delay periods. In this latter version, the monkey is not permitted to observe the experimenter baiting the food well. Therefore, to be correct on any given trial the monkey must remember which response was made last. In rats, spatial delayed alternation is a commonly used ► rodent test of cognition which exploits the ease with which rats can remember different locations and hence, have used spatial stimuli as in the
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