Dr. Salmon works at the forefront of neuropsychological research. He is a key investigator at the Shiley-Marcos Alzheimer's Disease Research Center, a large-scale collaborative program with long-term NIH funding. The major themes characterizing his research include (1) the early detection and accurate diagnosis of dementia and Alzheimer's disease (AD), (2) the differentiation of fronto-temporal dementia (FTD) from AD and the role of frontal systems dysfunction in AD, (3) the psychometric development of tests for detecting and tracking the progression of AD, (4) the nature of the semantic memory deficit in AD, and (5) the differences in the profiles of cognitive deficits associated with AD and the Lewy body variant (LBV) of AD.
Early detection: An initial study showed that the use of standardized diagnostic criteria and sensitive neuropsychological and functional measures allowed AD to be diagnosed with high accuracy in very mildly impaired individuals who scored > 24 on the Mini-Mental State Exam. The diagnosis of probable or possible AD was substantiated in 98/110 (89.1%) mildly demented subjects when the initial diagnosis was confirmed or refuted by subsequent autopsy verification or by progression consistent over two subsequent yearly evaluations. The importance of this study is that it demonstrates that the use of well defined clinical criteria can accurately predict a disease state even when only minimal dysfunction exists. Two additional studies in this series showed that the preclinical phase of AD known as Mild Cognitive Impairment is characterized by a greatly reduced episodic memory-mediated evoked response potential called the late positive component and by a precipitous decline in verbal memory abilities one to two years prior to the onset of the dementia syndrome. Early detection of dementia is becoming critical as a prelude to the development of primary prevention trials.
Fronto-temporal dementia: A second series of studies characterized the profile of cognitive deficits associated with FTD and examined the role of frontal systems dysfunction in AD. An initial study retrospectively compared patients with autopsy-confirmed FTD or AD in terms of the pattern of cognitive deficits they exhibited relatively early in the course of their diseases. Multivariate analysis revealed that FTD patients performed significantly worse than AD patients on tests of attention, but significantly better on tests of memory and visuospatial relations.
Psychometric development of tests: Three studies examined psychometric issues related to the detection and tracking of dementia associated with AD. The first study demonstrated the invalidity of using correlational or factor analytic procedures to identify the psychological constructs evaluated by neuropsychological assessment instruments. Important cognitive constructs assessed by a particular neuropsychological test were apparent when a factor analysis was carried out with data from a large group of AD patients, but were masked when the analysis was carried out for a group of normal control subjects. These results showed that cognitive measures that share considerable variance in normal individuals (e.g., immediate and delayed recall), giving the facade of assessing a unitary construct, can dissociate and contribute unique variance in the damaged brain.
Semantic memory deficit: Another series of studies addressed the nature of the semantic memory deficit in patients with AD. The first of these examined the effects of AD on the organization of semantic knowledge (i.e., the semantic network) for living (e.g., animals) and non-living (e.g., tools) categories. Multidimensional scaling of data from triadic comparison tasks showed that AD patients' semantic network for "tools" was essentially identical to that of normal control subjects, whereas their semantic network for "animals" was abnormal. A second study in this series showed that supplementary measures of semantic processing from a verbal fluency task were abnormal in patients with AD but were ineffective in distinguishing between those AD patients who showed significant cognitive decline over the subsequent year and those who remained stable. Thus, these process measures of verbal fluency performance may reflect the current state of the structure and ability to access semantic knowledge in AD patients, but they do not accurately forecast future rate of global cognitive decline.
Profiles of cognitive deficits associated with AD and the LBV of AD: Two recently completed studies further characterized the clinical and neuropsychological features of the LBV of AD and of Parkinson's disease (PD). One study compared the cognitive profiles on the Mattis Dementia Rating Scale (DRS) in patients with LBV, PD with dementia (PDD), progressive supranuclear palsy (PSP), and AD. Results showed no significant difference in the pattern of DRS subscores in the PDD and LBV groups, so a model was re-estimated after collapsing PDD and LBV into one category. The PDD-LBV patients had lower memory subscores than the PSP patients, but higher subscores than patients with AD. In contrast, PDD-LBV patients had significantly lower scores than the AD patients on the attention, initiation, conceptualization, and construction subtests, and higher scores than PSP patients on the construction subscale. This study is important in that, at present, clinicians are not able to accurately diagnose patients with LBV during life. This study makes an important contribution in identifying different neuropsychological profiles that can be used to improve the clinical diagnosis during life.
Dr. Salmon offers coursework at the graduate level, provides individual instruction, and teaches in the UCSD Continuing Education mini-residency programs and workshops. He has also taught the Proseminar in Neuropsychology of the SDSU-UCSD Joint Doctoral Program in Clinical Psychology.
Dr. Salmon is on the Editorial Boards of several major journals and routinely reviews articles. He has also served as a reviewer for several major national and international granting agencies. These include the Department of Veterans Affairs, NIMH, Medical Research Council of the United Kingdom, and Wellcome Trust of the United Kingdom. Other public service activities include participation as a member and as an ad hoc member of NIH study sections.