Accurate diagnosis of vascular dementia is important for the recognition of underlying pathophysiology and the institution of appropriate therapy. It is also important for the determination of the incidence and prevalence of not only vascular dementia but also Alzheimer's disease (AD), since differentiating between these two entities is often problematic. The State of California Alzheimer's Disease Diagnostic and Treatment Centers (ADDTC) herein propose criteria for the diagnosis of ischemic vascular dementia (IVD). These criteria broaden the conceptualization of vascular dementia, include the results of neuroimaging studies, emphasize the importance of neuropathologic confirmation, refine nosology, and identify areas that require further research. Parallel use of the proposed definitions of "possible" and "mixed" categories in the diagnosis of both AD and IVD would ensure compatibility between the National Institute of Neurological and Communicative Disorders and Stroke (NINCDS) criteria for AD and the ADDTC criteria for IVD. Uniform classification of subtypes of IVD will improve the generalizability of individual studies and aid in multicenter collaborations.

Neuropsychological data is reviewed in order to delineate the semantic, phonological, motor, and perceptual processes underlying spelling, with particular attention to handwriting. These data support a model in which semantic, lexical phonological, and non-lexical phonological processes can generate spelling, either independently or in an interactive fashion. Oral and written spelling depend upon common processes up to, and including, an orthographic code. After this point they each depend upon several separate stages of information processing.

This paper is concerned with the timing of regular repetitive movements. The two-process model of Wing and Kristofferson attributes variability in self-paced interresponse intervals to imprecision in a timekeeper and to temporal noise in the execution of motor responses triggered by the timekeeper. Assuming independence of timekeeper intervals and motor delays, the variance of each may be estimated from interresponse-interval statistics. Comparison of changes in timing performance associated with alterations in motor-system functioning offer the possibility of a new approach to investigation of this model. Illustrative data are presented from a case study of a patient with Parkinson's disease whose lesions affecting the dopaminergic pathways of the basal ganglia have given rise to asymmetric symptoms, including differences in timing performance of the two hands. Analysis of interresponse-interval variability according to the two-process model indicates that the elevated variability of the side more greatly affected by parkinsonism is attributable to the timekeeper intervals rather than the motor delays.

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