Imaging the dorsal hippocampus: light reflectance relationships to electroencephalographic patterns during sleep.
In the last decade, there has been a large growth of interest about the brain mechanisms that are associated with a number of psychological functions, including vision, hearing, movement preparation and execution, attention, memory, language, and emotions, among many others (Gazzaniga, 1995). The study of these mechanisms can be carried out at several different levels, from the molecular to the systemic (Marr, 1982). For each of these different levels, there are research instruments and approaches that are often specific to that level and vary along a number of dimensions, including invasiveness and spatial and temporal specificity (Churchland & Sejnowski, 1988). A major thrust of much of this research has been the development of noninvasive functional brain imaging methodologies with good spatial and temporal resolution, which allow investigators to study, more or less directly, the activity of the intact human brain (Posner & Raichle, 1994; Toga & Mazziotta, 1996). In this paper, we will review and discuss the role of imaging methods and their integration with psychological models of cognition. The focus will be on functional imaging techniques and, particularly, on their spatial and temporal resolution characteristics. Specifically, we will (1) consider the contexts in which functional imaging methods may be useful for the study of psychological functions, (2) briefly review and discuss the properties of the most widely used imaging methods, (3) introduce a new technology (the eventrelated optical signal, or EROS) that provides data with a good combination of spatial and temporal resolution, (4) outline some examples of the data that have been obtained with EROS to date, and (5) discuss the utility of combining imaging methods.