Our knowledge of the neurochemistry of human cognition is limited because of the lack of a reliable technique to study neurochemical changes associated with cognitive processing. We have recently shown that a modified molecular imaging technique offers a promising possibility. Using this technique we propose to study the aspects of human memory that are processed by dopaminergic system.
The goals of the study are to examine:
1. Whether the molecular imaging technique can be used to identify aspects of human memory that are processed by the striatal dopamine. We propose to study three forms of nonprocedural memory: associative, non-associative, and semantic. All of these forms of memory are impaired following striatal lesions.
2. Whether the controversy concerning striatal processing of nonprocedural memory can be resolved using molecular imaging technique. Since the technique will use a novel approach, it will provide information (concerning neurochemistry) that cannot be obtained by conventional imaging methods. Additional data acquired in this study will provide better insight into the role of the striatum and the dopamine system in human mnemonic processing.
Using a modified molecular imaging technique, striatal dopamine release during the performance of mnemonic tasks will be examined. In all of the experiments, after administration of a radiolabeled dopamine ligand (11C-raclopride), volunteers will be asked to perform one of the memory tasks. Concentration of the ligand during the task performance will be monitored dynamically using a PET camera, to estimate the release of dopamine in different striatal areas. The study will include following mnemonic tasks:
1. Associative memory: Using a paired associate paradigm, volunteers will be asked to retrieve the word that was previously associated with a cued word.
2. Non-associative memory: This will use a stem completion task in which volunteers will be asked to complete 3 letter word stems using a studied word.
3. Semantic memory: In this experiment, processing of semantically related words will be examined using a lexical decision task.