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The Aging Mind: Opportunities in Cognitive Research
(MEG), transcranial magnetic stimulation (TMS), electroencephalography (EEG), event-related brain potentials (ERP), and event-related optical signal (EROS), several of which so far are underutilized for the study of age-related cognitive changes, make breakthroughs possible in understanding brain-behavior links. Techniques such as fMRI and single-unit recording of neural activity are providing unprecedented levels of spatial and temporal resolution in observations of the brain, and other new and emerging techniques may hasten progress. Functional MRI, for example, can provide measurements in the brain with a time resolution of less than 1 second and spatial resolution of about 2 ram; technological advances promise further improvements in resolution (Le Bihan and Karni, 1995; Albright, Appendix G). Such techniques allow for much closer observation of neural phenomena than ever before, making possible much closer analysis of the relationships between neural and cognitive processes (e.g., Gabrieli, 1998).
Behavioral research has developed a rich array of laboratory techniques that isolate and measure specific mental operations that are fundamental to cognition. These techniques offer greater sensitivity and analytic power than traditional neuropsychological tests, which are designed to detect impairments but not to identify underlying processes and mechanisms. For example, experimental techniques have been used to demonstrate the distinct neural bases of implicit versus explicit memory in cognitive neuroscience research with patients (e.g., Gabrieli et al., 1995; Shimamura and Squire, 1984) and using imaging techniques (e.g., Uecker et al., 1997). The research demonstrates that implicit and explicit memory are differently affected by aging (Fleischman and Gabrieli, 1998; LaVoie and Light, 1994). Similarly, techniques for on-line evaluation of language comprehension processes have isolated semantic and syntactic processes required for comprehension (e.g., Marslen-Wilson and Tyler, 1980). These techniques have been central to evaluating the neural basis of comprehension in research with patients (e.g., Kempler et al., 1998) and using imaging techniques (Caplan et al., 1998, 1999). On-line measures of comprehension have provided evidence consistent with the maintenance of semantic comprehension processes in old age (e.g., Madden, 1988; Stine and Wingfield, 1994; see Burke, 1997; Light, 1991), although there is less agreement about syntactic processes (Caplan and Waters, 1999; Kemper and Kemptes, 1999; Stine-Morrow et al., 1996).
In animal research, tasks have been developed that are selectively sensitive to the effects of damage to the hippocampus, the amygdala, the caudate nucleus, the cerebellum, and the frontal cortex in rats. These tasks have since been adapted for the mouse and their research applications are being disseminated to researchers. For example, the Cold Spring Harbor Laboratories established an annual course in mouse behavior in 1998.
Because of the variety of behavioral tasks that are available, it is increasingly possible to use behavioral observations to identify specific brain regions