Model-based assessment and neural correlates of spatial memory deficits in mild cognitive impairment.

Mild cognitive impairment (MCI) is characterized by subjective and objective memory impairments within the context of generally intact everyday functioning. Such memory deficits are typically thought to arise from medial temporal lobe dysfunction; however, differences in memory task performance can arise from a variety of altered processes (e.g., strategy adjustments) rather than, or in addition to, "pure" memory deficits. To address this problem, we applied the linear ballistic accumulator (LBA: Brown and Heathcote, 2008) model to data from individuals with MCI (n = 18) and healthy older adults (HOA; n = 16) who performed an object-location association memory retrieval task during functional magnetic resonance imaging (fMRI). The primary goals were to 1) assess between-group differences in model parameters indexing processes of interest (memory sensitivity, accumulation speed, caution and time spent on peripheral perceptual and motor processes) and 2) determine whether differences in model-based metrics were consistent with fMRI data. The LBA provided evidence that, relative to the HOA group, those with MCI displayed lower sensitivity (i.e., difficulty discriminating targets from lures), suggestive of memory impairment, and displayed higher evidence accumulation speed and greater caution, suggestive of increased arousal and strategic changes in this group, although these changes had little impact on MCI-related accuracy differences. Consistent with these findings, fMRI revealed reduced activation in brain regions previously linked to evidence accumulation and to the implementation of caution reductions in the MCI group. Findings suggest that multiple cognitive mechanisms differ during memory retrieval in MCI, and that these mechanisms may explain neuroimaging alterations outside of the medial temporal lobes.

The Diagnostic and Prognostic Value of Neuropsychological Assessment in Memory Clinic Patients.

BACKGROUND: Neuropsychological testing has long been embedded in daily clinical practice at memory clinics but the added value of a complete neuropsychological assessment (NPA) to standard clinical evaluation is unknown. OBJECTIVE: To evaluate the added diagnostic and prognostic value of NPA to clinical evaluation only in memory clinic patients. METHODS: In 221 memory clinic patients of a prospective cohort study, clinical experts diagnosed clinical syndrome (subjective cognitive impairment (SCI), mild cognitive impairment (MCI), or dementia) and etiology (Alzheimer's disease (AD) or no AD), and provided a prognosis of disease course (decline or no decline) before and after results of NPA were made available. The reference standard was a panel consensus based on all clinical information at baseline and up to 2 follow-up assessments. RESULTS: With NPA data available, clinicians changed their initial syndromal diagnosis in 22% of patients, and the etiological diagnosis as well as the prognosis in 15%. This led to an increase in correctly classified cases of 18% for syndromal diagnosis, 5% for etiological diagnosis, and 1% for prognosis. NPA data resulted in the largest improvement in patients initially classified as SCI (syndrome: 93.3% (n = 14) correctly reclassified, etiology: net reclassification improvement [NRI] = 0.61, prognosis: NRI = 0.13) or MCI (syndrome: 89.3% (n = 23) correctly reclassified, etiology: NRI = 0.17, prognosis: NRI = 0.14), while there was no improvement in patients with dementia (syndrome: 100% (n = 1) correctly reclassified, etiology: NRI = -0.05, prognosis: NRI = -0.06). Overall, inclusion of NPA in the diagnostic process increased confidence in all diagnoses with 6-7%. CONCLUSION: Administration of a complete NPA after standard clinical evaluation has added value for diagnosing cognitive syndrome and its underlying etiology in patients regarded as non-demented based on the first clinical impression.

[Vitamin D and neuropsychological assessment of cognitive functions: a study of their relationships in a sample of 244 patients attending a memory clinic]. / Vitamine D et évaluation neuropsychologique des fonctions cognitives : étude chez 244 sujets âgés pris en charge en hôpital de jour mémoire.

There is evidence of a role of vitamin D in cognitive functioning, but little is known about the type of functions involved. To describe vitamin D status in a population of old patients with memory complaints and its relationships with cognitive performance and white matter lesions. A retrospective single-centre observational study from the medical records of 244 patients who had a measurement of serum 25OHD together with a battery of neuropsychological tests during a complete geriatric and memory assessment in a day care hospital. The results of the 10 neuropsychological tests considered in this study were analysed as binary variables, opposing patients with results within the highest two tertiles to patients with the worse results or unable to perform the test. Mean age of people included was 80.2 ± 8.1 years and 64% of patients were women. Severe deficiency in vitamin D (25OHD <10 ng/mL) was found in 34 patients (13.9%) and moderate deficiency (10 ≤ 25OHD < 30 ng/mL) in 148 (60.7%). Compared to subjects with sufficient concentrations in vitamin D, patients with severe deficiency performed significantly worse on a global test, the Mini mental state examination, and two tests of verbal memory, the 5 words and the 16-item free and cued recall, independently from age, gender, education, body mass index and autonomy (OR = 2.85 [1.04-7.85], 4.31 [1.42-13.07], and 3.04 [1.01-9.19] respectively). Levels of vitamin D did not differ according to the extent of white matter lesions, visualized semi-quantitatively on magnetic resonance imaging of 115 subjects. This study confirms the high prevalence of vitamin D deficiency in elderly population and suggests a link between vitamin D deficiency and memory.

Visual assessment of [(11)C]PIB PET in patients with cognitive impairment.

PURPOSE: The aim of this study was to evaluate the visual assessment of positron emission tomography images of N-[methyl-11C]2-(4'-methylaminophenyl)-6-hydroxybenzothiazole ([11C]PIB) in a patient population with mild to moderate memory impairment or dementia. METHODS: We compared the visual ratings of two readers using kappa statistics and correlated the results of visual and quantitative region of interest (ROI) analyses. The one reader had good experience in evaluating PIB images and the other had little previous experience. The sensitivity and specificity of the visual assessment was determined using quantitative data from 18 healthy controls previously examined: [11C]PIB uptake was considered as abnormal if it was more than 2 SD above the mean of the healthy subjects. RESULTS: The evaluation of visual classification as "normal" or "abnormal" showed good interobserver agreement (kappa = 0.90). There was a clear correlation between visual and quantitative analysis (r = 0.47-0.79, p < 0.001). The most difficult visually assessed brain area was the putamen (kappa = 0.11; correlation with quantitative analysis: reader A r = 0.22; reader B r = 0.60). CONCLUSION: Our study shows that visual evaluation of [(11)C]PIB images conforms with quantitative analyses also in a clinical patient population supporting the feasibility of visual evaluation in clinical settings.

Decreased hippocampal blood flow related to memory impairment after cardiovascular surgery: assessment by reconstructed SPECT parallel to the longitudinal axis of the hippocampal formations.

Hippocampal damage has been linked to memory impairment. To clarify the relationship between decreased hippocampal blood flow and memory impairment in patients after cardiovascular surgery, the authors compared Tc-99m HMPAO SPECT findings and Mini Mental State Examination (MMSE) scores. Eight patients who had valve replacement, two who underwent aorto-coronary bypass, two who had aortic aneurysm replacement and one who had a ventricular septal defect closure were included in this study. Cerebral perfusion was estimated using reconstructed tomographic images, which were parallel to the longitudinal axis of the hippocampal formations. The hippocampal uptake ratios of Tc-99m HMPAO were calculated and normalized to that of the cerebellum. In three patients whose MMSE score decreased after surgery, the hippocampal uptake ratio was significantly reduced (0.69 +/- 0.09) compared with the remaining 10 patients whose MMSE scores did not decrease after surgery (0.91 +/- 0.02). These data suggest that SPECT imaging parallel to the longitudinal axis of the hippocampus is sensitive to decreased hippocampal blood flow, and decreased hippocampal blood flow is related to memory impairment in some patients after cardiovascular surgery.