Patterns of brain activation in people at risk for Alzheimer's disease

Role of white matter lesions, cerebral atrophy, and APOE on cognition in older persons with and without dementia: the Cache County, Utah, study of memory and aging

Neuropsychological, qualitative, and quantitative magnetic resonance imaging findings were examined in subjects with Alzheimer's disease (AD), non-AD dementia or mixed neuropsychiatric disorder, subjects characterized as mild/ambiguous, and controls, all with known apolipoprotein E (APOE) genotype. Neuropsychological tasks included an expanded Consortium to Establish a Registery for Alzheimer's Disease (J. T. Tschanz et al., 2000; K. A. Welsh, J. M. Hoffman, N. L. Earl, & M. W. Hanson 1994) battery and the Mini-Mental Status Examination (M. F. Folstein, S. E. Folstein, & P. R. McHugh, 1975). Periventricular white matter lesions were the most clinically salient, and generalized measures of cerebral atrophy were the most significant quantitative indicators. APOE genotype was unrelated to imaging or neuropsychological performance. Neuropsychological relationships with neuroimaging findings depend on the qualitative or quantitative method used.

Voxel- and VOI-based analysis of SPECT CBF in relation to clinical and psychological heterogeneity of mild cognitive impairment

This study aimed to explore the heterogeneity of mild cognitive impairment (MCI) and detect differences in regional cerebral blood flow (rCBF) and cognitive function between progressive mild cognitive impairment (PMCI) and stable mild cognitive impairment (SMCI) in order to identify specific changes useful for early diagnosis of dementia. SPECT was performed in 82 MCI subjects and 20 controls using Tc-99m hexamethylpropyleneamine oxime. Cognitive functions were tested in five domains which included episodic memory, semantic memory, visuospatial function, attention, and general cognitive function. After the initial examination, MCI subjects were clinically followed for an average of 2 years. Twenty-eight subjects progressed to dementia and were defined as PMCI at baseline and 54 subjects remained stable and were defined as SMCI at baseline. The baseline rCBF and cognitive function of PMCI, SMCI, and controls were compared. PMCI had decreased relative rCBF in the parietal lobes and increased relative rCBF in prefrontal cortex compared to SMCI and controls at baseline. The cognitive function of PMCI was more severely impaired compared to SMCI with respect to episodic memory and visuospatial and general cognitive function. Both SPECT and neuropsychological tests had moderate discriminant function between PMCI and SMCI at baseline with the area under the receiver operating characteristic (ROC) curve at 75-77%. The combination of these two methods improved the diagnostic accuracy with the area under the ROC curve at 82-84%. Semantic memory and attention were negatively correlated with left prefrontal relative rCBF among the study population. The results show that the clinical heterogeneity of MCI is reflected in different patterns of psychological and CBF changes. Combined SPECT investigation and neuropsychological testing might predict the future development of dementia in patients with MCI.

[Radiologic diagnostics of dementia]

Dementia is one of the most common diseases in the elderly population and is getting more and more important with the ageing of the population. A radiologic structural examination with CT or MRI is meanwhile a standard procedure in the diagnostic work up of patients with dementia syndrome. Radiology enables an early diagnosis and a differential diagnosis between different causes of dementia. Because structural changes occur only late in the disease process, a more detailed structural analysis using volumetric techniques or the use of functional imaging techniques is mandatory. These days, structural imaging uses MRI which enables to detect early atrophic changes at the medial temporal lobe with focus on the amygdala hippocampal complex. These changes are also present in the normal ageing process. In patients with Alzheimer's disease, however, they are more rapid and more pronounced. The use of functional imaging methods such as perfusion MRI, diffusion MRI or fMRI allow new insights into the pathophysiologic changes of dementia. The article gives an overview of the current status of structural imaging and an outlook into the potential of functional imaging methods. Detailed results of structural and functional imaging are presented in other articles of this issue.

Novel ROC-type method for testing the efficiency of multivariate statistical methods in fMRI

The receiver operating characteristic (ROC) method is a useful and popular tool for testing the efficiency of various diagnostic tests applicable to functional MRI (fMRI) data. Typically, the diagnostic tests are applied on simulated and pseudo-human fMRI data, and the area under the ROC curve is used as a measure of the efficiency of the diagnostic test. The effectiveness of such a method depends on how well the simulated data approximate the real data. For multivariate statistical methods, however, this technique is usually inadequate, as the spatial dependence among voxels is ignored for simulated data. In this work a modified ROC method using real fMRI data with a broader scope is proposed. This method can be applied to most fMRI postprocessing techniques, including multivariate analyses such as canonical correlation analysis (CCA). Also, the relationship of the modified ROC method with the conventional ROC method is discussed in detail.

Schizophrenia: from phenomenology to neurobiology

Schizophrenia is a common and debilitating illness, characterized by chronic psychotic symptoms and psychosocial impairment that exact considerable human and economic costs. The literature in electronic databases as well as citations and major articles are reviewed with respect to the phenomenology, pathology, treatment, genetics and neurobiology of schizophrenia. Although studied extensively from a clinical, psychological, biological and genetic perspective, our expanding knowledge of schizophrenia provides only an incomplete understanding of this complex disorder. Recent advances in neuroscience have allowed the confirmation or refutation of earlier findings in schizophrenia, and permit useful comparisons between the different levels of organization from which the illness has been studied. Schizophrenia is defined as a clinical syndrome that may include a collection of diseases that share a common presentation. Genetic factors are the most important in the etiology of the disease, with unknown environmental factors potentially modulating the expression of symptoms. Schizophrenia is a complex genetic disorder in which many genes may be implicated, with the possibility of gene-gene interactions and a diversity of genetic causes in different families or populations. A neurodevelopmental rather than degenerative process has received more empirical support as a general explanation of the pathophysiology, although simple dichotomies are not particularly helpful in such a complicated disease. Structural brain changes are present in vivo and post-mortem, with both histopathological and imaging studies in overall agreement that the temporal and frontal lobes of the cerebral cortex are the most affected. Functional imaging, neuropsychological testing and clinical observation are also generally consistent in demonstrating deficits in cognitive ability that correlate with abnormalities in the areas of the brain with structural abnormalities. The dopamine and other neurotransmitter systems are certainly involved in the treatment or modulation of psychotic symptoms. These broad findings represent the distillation of a large body of disparate data, but firm and specific findings are sparse, and much about schizophrenia remains unknown.

Pathology and pathways of Alzheimer's disease with an update on new developments in treatment

As our understanding of the complex pathology of Alzheimer's disease improves, more targets for therapy emerge. These include the actions of beta amyloid, the inflammatory cascade, pathobiology of tau proteins' conversion to neurofibrillary tangles, oxidative neuronal damage, and neurotransmitter depletion. Many agents now under investigation target the early stages of the disease process, aiming to prevent or slow the development of symptoms. This article reviews the current understanding of the course and pathology of Alzheimer's disease as it relates to emerging therapies, then summarizes some promising current research directions in primary prevention, secondary prevention, and treatment.

Age-related mild cognitive deficit: a ready-to-use concept?

For better management of mild cognitive impairment in elderly patients, clinicians should be provided with instruments to detect early changes and predict their progression. To define this cognitive status between optimal and pathological aging, many concepts have been proposed, which actually describe various conditions and provide more or less precise criteria, leaving room for variable implementation. As a consequence, application of these criteria gave highly variable prevalence rates, Neuropathological studies indicate that the different criteria have variable power in detecting incipient Alzheimer's disease (AD) and suggest that the transition between mild cognitive impairment and ÀD is not merely quantitative. Follow-up studies have produced, according to the criteria used, a 2.5% to 16,6% annual rate for progression toward dementia, and have also shown that the criteria differ in their stability and predictive power. Baseline cognitive performances have some predictive value, but are difficult to apply in first-line medicine. Investigational techniques (structural and functional imaging, magnetic resonance spectroscopy, magnetization transfer imaging, cerebrospinal fluid neuro-chemistry, and apolipoprotein E genotype) are promising tools in the early diagnosis of AD, which remains the most frequent type of dementia in elderly people and probably the most frequent type developed by patients with mild cognitive deficit. The final goal is to offer early treatment to those patients who will evolve towards dementia, once they can be identified, in the case of AD, recent findings question the adequacy of cholinergic replacement therapies. In its current state, the criteria for mild cognitive deficit are hardly transferable to first-line medicine. However, disseminating the concept could help increase the sensitivity of general practitioners to the importance of cognitive complaints and signs in their elderly patients.

Neuroimaging and early diagnosis of Alzheimer disease: a look to the future

Alzheimer disease (AD), a progressive neurodegenerative disorder, is the most common cause of dementia in the elderly. Current consensus statements have emphasized the need for early recognition and the fact that a diagnosis of AD can be made with high accuracy by using clinical, neuropsychologic, and imaging assessments. Magnetic resonance (MR) or computed tomographic (CT) imaging is recommended for the routine evaluation of AD. Coronal MR images can be useful to document or quantify atrophy of the hippocampus and entorhinal cortex, both of which occur early in the disease process. Both volumetric and subtraction MR techniques can be used to quantify and monitor dementia progression and rates of regional atrophy. MR measures are also increasingly being used to monitor treatment effects in clinical trials of cognitive enhancers and antidementia agents. Positron emission tomography (PET) and single photon emission CT offer value in the differential diagnosis of AD from other cortical and subcortical dementias and may also offer prognostic value. In addition, PET studies have demonstrated that subtle abnormalities may be apparent in the prodromal stages of AD and in subjects who carry susceptibility genes. PET ligands are in late-stage development for demonstration of amyloid plaques, and human studies have already begun. Functional MR-based memory challenge tests are in development as well.

The BDNF val66met polymorphism affects activity-dependent secretion of BDNF and human memory and hippocampal function

Brain-derived neurotrophic factor (BDNF) modulates hippocampal plasticity and hippocampal-dependent memory in cell models and in animals. We examined the effects of a valine (val) to methionine (met) substitution in the 5' pro-region of the human BDNF protein. In human subjects, the met allele was associated with poorer episodic memory, abnormal hippocampal activation assayed with fMRI, and lower hippocampal n-acetyl aspartate (NAA), assayed with MRI spectroscopy. Neurons transfected with met-BDNF-GFP showed lower depolarization-induced secretion, while constitutive secretion was unchanged. Furthermore, met-BDNF-GFP failed to localize to secretory granules or synapses. These results demonstrate a role for BDNF and its val/met polymorphism in human memory and hippocampal function and suggest val/met exerts these effects by impacting intracellular trafficking and activity-dependent secretion of BDNF.

Modulation of Alzheimer-like synaptic and cholinergic deficits in transgenic mice by human apolipoprotein E depends on isoform, aging, and overexpression of amyloid beta peptides but not on plaque formation

The most frequent human apolipoprotein (apo) E isoforms, E3 and E4, differentially affect Alzheimer's disease (AD) risk (E4 > E3) and age of onset (E4 < E3). Compared with apoE3, apoE4 promotes the cerebral deposition of amyloid beta (Abeta) peptides, which are derived from the amyloid precursor protein (APP) and play a central role in AD. However, it is uncertain whether Abeta deposition into plaques is the main mechanism by which apoE isoforms affect AD. We analyzed murine apoE-deficient transgenic mice expressing in their brains human APP (hAPP) and Abeta together with apoE3 or apoE4. Because cognitive decline in AD correlates better with decreases in synaptophysin-immunoreactive presynaptic terminals, choline acetyltransferase (ChAT) activity, and ChAT-positive fibers than with plaque load, we compared these parameters in hAPP/apoE3 and hAPP/apoE4 mice and singly transgenic controls at 6-7, 12-15, and 19-24 months of age. Brain aging in the context of high levels of nondeposited human Abeta resulted in progressive synaptic/cholinergic deficits. ApoE3 delayed the synaptic deficits until old age, whereas apoE4 was not protective at any of the ages analyzed. Old hAPP/apoE4 mice had more plaques than old hAPP/apoE3 mice, but synaptic/cholinergic deficits preceded plaque formation in hAPP/apoE4 mice. Moreover, despite their different plaque loads, old hAPP/apoE4 and hAPP/apoE3 mice had comparable synaptic/cholinergic deficits, and these deficits were found not only in the hippocampus but also in the neocortex, which in most mice contained no plaques. Thus, apoE3, but not apoE4, delays age- and Abeta-dependent synaptic deficits through a plaque-independent mechanism. This difference could contribute to the differential effects of apoE isoforms on the risk and onset of AD.

Coupled reductions in brain oxidative phosphorylation and synaptic function can be quantified and staged in the course of Alzheimer disease

In vivo, post-mortem and biopsy data suggest that coupled declines occur in brain synaptic activity and brain energy consumption during the evolution of Alzheimer disease. In the first stage of these declines, changes in synaptic structure and function reduce neuronal energy demand and lead to potentially reversible downregulation of oxidative phosphorylation (OXPHOS) within neuronal mitochondria. At this stage, measuring brain glucose metabolism or brain blood flow in patients, using positron emission tomography (PET), shows that the brain can be almost normally activated in response to stimulation. Thus, therapy at this stage should be designed to re-establish synaptic integrity or prevent its further deterioration. As disease progresses, neurofibrillary tangles with abnormally phosphorylated tau protein accumulate within neuronal cytoplasm, to the point that they co-opt the nonphosphorylated tau necessary for axonal transport of mitochondria between the cell nucleus and the synapse. In this second stage, severe energy depletion and other pathological processes associated with irreversibly downregulated OXPHOS lead to cell death, and the brain cannot normally respond to functional stimulation.

Evaluation of dementia in the cardiovascular health cognition study

OBJECTIVE

To describe a methodology to evaluate dementia and frequency of different types of dementia and prevalence of the Cardiovascular Health Study (CHS).

METHODS

The CHS is a longitudinal study of cardiovascular disease among community-dwelling individuals over the age of 65. Of the 5,888 participants in the original study, 3,608 had a magnetic resonance imaging (MRI) of the brain in 1991, and formed the cohort for the dementia study. The CHS included yearly measures of cognitive function and, from 1998 to 2000, participants were evaluated for dementia by detailed neurological, and neuropsychological examinations. The possible cases of dementia and mild cognitive impairment (MCI) were adjudicated by a review committee of neurologists and psychiatrists.

RESULTS

There were 480 cases of (13.3%) incident dementia in the total sample, 227 (6.3%) prevalent dementia, 577 (16.0%) MCI, and 2,318 (64.4%) normal. The adjudication committee classified 69% of the incident dementia as Alzheimer's disease (AD), 11% as vascular dementia (VaD), 16% as both, and 4% as other types. There was a substantial agreement between pre- and postMRI diagnosis of types of dementia. The frequency of dementia within the CHS cohort which survived to the end of the study in 1998-1999, was 13.5% for white men, 14.5% for white women, 22.2% for black men and 23.4% for black women.

CONCLUSION

The CHS has developed a methodology for longitudinal studies of dementia in large cohorts and represents the largest study of dementia including cognitive testing, MRI and genetic markers.

Advanced brain imaging procedures and human memory disorder

The impact of advanced brain imaging procedures in the field of human memory disorder is reviewed, with particular emphasis on current and potential applications that may impact upon the diagnosis and management of memory-disordered patients. While both advanced structural, resting physiological and functional physiological brain imaging procedures have been applied to conditions where memory disorder is a major feature, the specific implications of research findings for diagnosis and treatment in routine clinical practice remain tentative and promising, but not yet substantive enough to inform clinical decisions to a significant degree. In terms of diagnostic applications, several promising areas include dementia, epilepsy, and transient amnesic states. In the case of applications in treatment settings, advanced brain imaging procedures may help to monitor neural correlates of spontaneous recovery or progression of memory function, and may also help in the planning and monitoring of therapeutic intervention.

Risk factors for dementia in the cardiovascular health cognition study

BACKGROUND

The Cardiovascular Health Cognition Study has evaluated the determinants of dementia among 3,608 participants that had a magnetic resonance imaging (MRI) of the brain in 1991 and were followed to 1998-1999.

METHODS

There were 480 incident dementia cases, 330 (69%) were classified as Alzheimer's disease (AD).

RESULTS

In univariate analysis, low scores on the Modified Mini-Mental State Examination (3MSE) and on the Digit Symbol Substitution Test as well as declines in scores over time prior to the development of dementia were significant predictors of dementia. A high ventricular grade on the MRI (atrophy) as well as high white matter grade, a number of brain infarcts on the MRI were all determinants of dementia. Apolipoprotein E epsilon4 (Apo(E-4)) was also a powerful predictor of dementia. In a multivariate Cox proportional hazards model controlling for race, gender and grade, the hazard ratios for age (1.1), 3MSE score (0.9), ventricular size (1.4), white matter grade (1.8), presence of large infarcts >3 mm (1.3) and Apo(E-4) (2.1) were significant predictors of dementia. The combination of an Apo(E-4) genotype, 3MSE score <90, > or =5 ventricular grade, > or =3 white matter grade at the time of the MRI were associated with a 17-fold increased risk (95% CI: 8.6-34.9) of dementia as compared to individuals with none of the above attributes.

CONCLUSIONS

Measures of cognition, Apo(E-4) and MRI of the brain are strong predictors of both dementia and of AD.

Imaging genomics

The recent completion of a working draft of the human genome sequence promises to provide unprecedented opportunities to explore the genetic basis of individual differences in complex behaviours and vulnerability to neuropsychiatric illness. Functional neuroimaging, because of its unique ability to assay information processing at the level of brain within individuals, provides a powerful approach to such functional genomics. Recent fMRI studies have established important physiological links between functional genetic polymorphisms and robust differences in information processing within distinct brain regions and circuits that have been linked to the manifestation of various disease states such as Alzheimer's disease, schizophrenia and anxiety disorders. Importantly, all of these biological relationships have been revealed in relatively small samples of healthy volunteers and in the absence of observable differences at the level of behaviour, underscoring the power of a direct assay of brain physiology like fMRI in exploring the functional impact of genetic variation.

fMRI studies of associative encoding in young and elderly controls and mild Alzheimer's disease

OBJECTIVE

To examine alterations in patterns of brain activation seen in normal aging and in mild Alzheimer's disease by functional magnetic resonance imaging (fMRI) during an associative encoding task.

METHODS

10 young controls, 10 elderly controls, and seven patients with mild Alzheimer's disease were studied using fMRI during a face-name association encoding task. The fMRI paradigm used a block design with three conditions: novel face-name pairs, repeated face-name pairs, and visual fixation.

RESULTS

The young and elderly controls differed primarily in the pattern of activation seen in prefrontal and parietal cortices: elderly controls showed significantly less activation in both superior and inferior prefrontal cortices but greater activation in parietal regions than younger controls during the encoding of novel face-name pairs. Compared with elderly controls, the Alzheimer patients showed significantly less activation in the hippocampal formation but greater activation in the medial parietal and posterior cingulate regions.

CONCLUSIONS

The pattern of fMRI activation during the encoding of novel associations is differentially altered in the early stages of Alzheimer's disease compared with normal aging.

Mild cognitive impairment: conceptual issues and structural and functional brain correlates

Mild cognitive impairment (MCI) is a prevalent condition among older adults that carries a high risk of progression to Alzheimer's disease or other dementias. Given the potential for delaying or preventing the onset of dementia, efforts aimed at early detection and early intervention are important. The current paper reviews the conceptualization and diagnosis of MCI, assessment of memory complaints and deficits in the elderly, as well as recent research on the neurobiological basis of the disorder, including neurochemical, structural, and functional neuroimaging findings.

Modulation of Alzheimer-like synaptic and cholinergic deficits in transgenic mice by human apolipoprotein E depends on isoform, aging, and overexpression of amyloid beta peptides but not on plaque formation

The most frequent human apolipoprotein (apo) E isoforms, E3 and E4, differentially affect Alzheimer's disease (AD) risk (E4 > E3) and age of onset (E4 < E3). Compared with apoE3, apoE4 promotes the cerebral deposition of amyloid beta (Abeta) peptides, which are derived from the amyloid precursor protein (APP) and play a central role in AD. However, it is uncertain whether Abeta deposition into plaques is the main mechanism by which apoE isoforms affect AD. We analyzed murine apoE-deficient transgenic mice expressing in their brains human APP (hAPP) and Abeta together with apoE3 or apoE4. Because cognitive decline in AD correlates better with decreases in synaptophysin-immunoreactive presynaptic terminals, choline acetyltransferase (ChAT) activity, and ChAT-positive fibers than with plaque load, we compared these parameters in hAPP/apoE3 and hAPP/apoE4 mice and singly transgenic controls at 6-7, 12-15, and 19-24 months of age. Brain aging in the context of high levels of nondeposited human Abeta resulted in progressive synaptic/cholinergic deficits. ApoE3 delayed the synaptic deficits until old age, whereas apoE4 was not protective at any of the ages analyzed. Old hAPP/apoE4 mice had more plaques than old hAPP/apoE3 mice, but synaptic/cholinergic deficits preceded plaque formation in hAPP/apoE4 mice. Moreover, despite their different plaque loads, old hAPP/apoE4 and hAPP/apoE3 mice had comparable synaptic/cholinergic deficits, and these deficits were found not only in the hippocampus but also in the neocortex, which in most mice contained no plaques. Thus, apoE3, but not apoE4, delays age- and Abeta-dependent synaptic deficits through a plaque-independent mechanism. This difference could contribute to the differential effects of apoE isoforms on the risk and onset of AD.

Mild cognitive impairment in older people

CONTEXT

As public awareness of Alzheimer's disease increases, more people are asking for help and advice about memory problems. Memory complaints may be secondary to psychiatric, psychological, and physical conditions and is an almost universal early symptom of dementia. The concept of amnestic mild cognitive impairment attempts to describe those people in whom memory loss is not of such severity to merit a diagnosis of dementia. The importance of this group of people is not just the need to develop interventions which ameliorate individual suffering but that they represent a population at high risk of developing dementia, especially Alzheimer's disease, and are an appropriate target for dementia prevention strategies.

STARTING POINT

K Kantarci and colleagues (Dement Geriatr Cogn Disord 2002; 14: 198-207) looked at the diagnostic accuracy of magnetic-resonance hippocampal volumetry and spectroscopy in patients with mild cognitive impairment, in normal older people, and in patients with Alzheimer's disease. Hippocampal volumes and N-acetyl aspartate/creatine spectroscopy were the most sensitive assessments discriminating people with mild cognitive impairment from Alzheimer's disease. Combination assessments were better at discriminating these two groups from normal controls. The histological underpinning of cognitive symptoms in older people has been demonstrated by the Cognitive Function and Ageing study (Lancet 2001; 357: 169-75), which showed that a third of people with no clinical evidence of dementia had histopathological hallmarks of Alzheimer's disease. WHERE NEXT? 25 million people across the world have dementia. Mild cognitive impairment, if a validated concept, represents an opportunity for preventing dementia. As more information becomes available about the cause of Alzheimer's disease and prospects emerge for prevention, identification of predementia states offers considerable scope to reduce the individual and societal cost of the illness. Continued validation of the criteria for mild cognitive impairment and studies of intervention should be a priority. As more evidence becomes available highlighting the relatively arbitrary nature of dementia diagnosis (based largely on interference with activities) and interventions become available for the prevention of dementia, mild cognitive impairment and related conditions will become more important.

Use of neuroimaging to detect early brain changes in people at genetic risk for Alzheimer's disease

The neuropathological and cognitive changes preceding Alzheimer's disease appear to begin subtly decades before symptoms of the disease make the clinical diagnosis obvious. Clinical trials have begun to focus on preventive treatments designed to slow age-related cognitive decline and delay the onset of Alzheimer's disease in people with only mild memory complaints. Because people with few cognitive deficits represent a heterogeneous population, prevention studies require large samples in order to detect active drug effects. To address such challenges, recent neuroimaging studies have focused on middle-aged and older adults with only mild memory complaints and evaluated results according to the major known genetic risk for Alzheimer's disease, the apolipoprotein E-4 (APOE-4) allele. In studies using positron emission tomography during mental rest and functional magnetic resonance imaging during memory task performance, brain patterns differ according to genetic risk and are useful in predicting future decline measures and following disease progression in clinical trials.

Vascular disorder in Alzheimer's disease: role in pathogenesis of dementia and therapeutic targets

It is not clear whether Alzheimer's Disease (AD) is primarily a neurodegenerative disorder or not. A body of evidence suggests that vascular disorder in brains of individuals with AD contributes to the extremes of this disease. This raises a question whether Alzheimer's dementia is secondary to vascular dysfunction in the central nervous system (CNS) and, therefore, the neurodegeneration that follows is a consequence of inadequate cerebral blood flow, altered brain metabolism and failure in physiological functions of brain endothelium which represents a site at the blood-brain barrier (BBB). In this paper the evidence for a primary role of the CNS vascular system in pathogenesis of Alzheimer's dementia is reviewed to show how alterations in transport across the BBB contribute to development of cerebral beta-amyloidosis in AD. In addition, vascularly-based therapeutic strategies to limit the development of beta-amyloidosis and to remove amyloid and plaques from the CNS of AD individuals are discussed.

Ethical, and practical issues in applying functional imaging to the clinical management of Alzheimer's disease

This review outlines ethical, legal, and practical issues related to conducting functional imaging research with Alzheimer's disease (AD) patients. Imaging techniques, with an emphasis on functional MRI and positron emission tomography, are compared and contrasted with respect to the manner in which they can be applied to issues of clinical relevance to AD. Methodological difficulties are raised to assist with critical evaluation of current imaging results. Various potential clinical applications of functional imaging are briefly reviewed and discussed with respect to associated ethical conflicts.

Functional imaging of visuospatial processing in Alzheimer's disease

Alzheimer's disease (AD) is known to cause a variety of disturbances of higher visual functions that are closely related to the neuropathological changes. Visual association areas are more affected than primary visual cortex. Additionally, there is evidence from neuropsychological and imaging studies during rest or passive visual stimulation that the occipitotemporal pathway is less affected than the parietal pathway. Our goal was to investigate functional activation patterns during active visuospatial processing in AD patients and the impact of local cerebral atrophy on the strength of functional activation. Fourteen AD patients and fourteen age-matched controls were measured with functional magnetic resonance imaging (fMRI) while they performed an angle discrimination task. Both groups revealed overlapping networks engaged in angle discrimination including the superior parietal lobule (SPL), frontal and occipitotemporal (OTC) cortical regions, primary visual cortex, basal ganglia, and thalamus. The most pronounced differences between the two groups were found in the SPL (more activity in controls) and OTC (more activity in patients). The differences in functional activation between the AD patients and controls were partly explained by the differences in individual SPL atrophy. These results indicate that parietal dysfunction in mild to moderate AD is compensated by recruitment of the ventral visual pathway. We furthermore suggest that local cerebral atrophy should be considered as a covariate in functional imaging studies of neurodegenerative disorders.

Decline in verbal memory during preclinical Alzheimer's disease: examination of the effect of APOE genotype

A subtle decline in episodic memory often occurs prior to the emergence of the full dementia syndrome in nondemented older adults who develop Alzheimer's disease (AD). The APOE-epsilon4 genotype may engender a more virulent form of AD that hastens this decline. To examine this possibility, we compared the rate of decline in episodic memory during the preclinical phase of AD in individuals with or without at least one APOE epsilon4 allele. Nondemented normal control (NC; n = 84) participants, nondemented older adults who subsequently developed dementia within 1 or 2 years (i.e., preclinical AD; n = 20), and patients with mild AD (n = 53) were examined with 2 commonly employed tests of episodic memory, the Logical Memory subtest of the Wechsler Memory Scale-Revised and the California Verbal Learning Test. Results revealed a precipitous decline in verbal memory abilities 1 to 2 years prior to the onset of the dementia syndrome, but there was little effect of APOE genotype on the rate of this memory decline. The presence of an APOE-epsilon4 allele, however, did have a differential effect on the sensitivity of the 2 types of memory tests for tracking progression and made an independent contribution to the prediction of conversion to AD.

Brain activation during smooth-pursuit eye movements

A potential application of studying eye movements with functional MRI (fMRI) is to examine patient populations with known eye movement dysfunction, but the reliability with which normal subjects demonstrate activity in specific brain regions has not been established. To date, fMRI studies of smooth-pursuit eye movements have used relatively small numbers of subjects and have been restricted to fixed-effects analyses. We extend these studies to whole brain imaging at 1.5 T, properly accounting for intersubject variation using random effects analysis. Smooth-pursuit eye movements elicited activation consistently in dorsal cortical eye fields and cerebellum. Subcortical activation was greatly attenuated, but not eliminated, with the random-effects second-level analysis. In addition, session-dependent changes in activation were greater in some regions than others and may indicate areas of brain, such as the supplementary eye fields, that are sensitive to attentional modulation of eye movements.

The apolipoprotein E gene, attention, and brain function

The epsilon4 allele of the apolipoprotein E (ApoE) gene is associated with alterations in brain function and is a risk factor for Alzheimer's disease (AD). Changes in components of visuospatial attention with ApoE-epsilon4, aging, and AD are described. Healthy middle-aged adults without dementia who have the ApoE-epsilon4 gene show deficits in spatial attention and working memory that are qualitatively similar to those seen in clinically diagnosed AD patients. The findings support an association between ApoE polymorphism and specific components of visuospatial attention. Molecular mechanisms that may mediate the ApoE-attention link by modulating cholinergic neurotransmission to the posterior parietal cortex are discussed. Studies of attention and brain function in ApoE-epsilon4 carriers without dementia can advance knowledge of the genetics of visual attention, may enhance understanding of the preclinical phase of AD, and may lead to better methods for early AD detection.

Alzheimer's disease is a synaptic failure

In its earliest clinical phase, Alzheimer's disease characteristically produces a remarkably pure impairment of memory. Mounting evidence suggests that this syndrome begins with subtle alterations of hippocampal synaptic efficacy prior to frank neuronal degeneration, and that the synaptic dysfunction is caused by diffusible oligomeric assemblies of the amyloid beta protein.

Alzheimer Disease: evaluation of a functional MR imaging index as a marker

PURPOSE

To measure changes in functional synchrony in the hippocampus in patients with mild cognitive impairment (MCI) and Alzheimer disease (AD).

MATERIALS AND METHODS

Three subject groups (nine cognitively healthy elderly control subjects, 10 patients with probable AD, and five subjects with MCI) underwent resting-state functional magnetic resonance (MR) imaging for measurement of functional synchrony in the hippocampus. Functional synchrony was defined and quantified as the mean of the cross-correlation coefficients of spontaneous low frequency (COSLOF) components between possible pairs of voxel time courses in a brain region, or the COSLOF index. The two-tailed Student t test was used to determine differences in the COSLOF index between the control group, the probable AD group, and the MCI group. An operating characteristic curve was calculated to graphically depict the tradeoff between sensitivity and specificity of the COSLOF index.

RESULTS

Functional synchrony quantified with the COSLOF index was obtained in AD, MCI, and control subjects. COSLOF index values were significantly lower in AD patients than in control subjects (t = 4.32, P <.0012). For MCI subjects, COSLOF index values were significantly higher than those of AD patients (t = -2.4052, P <.047) but significantly lower than those of control subjects (t = 2.257, P <.043). The exponential-class curve significantly fits the relationship between the COSLOF index and the Mini-Mental Status Examination score (chi(2) = 20.4), indicating the rapid decrease in cognitive capacity below a threshold of the COSLOF index.

CONCLUSION

Our results suggest that the COSLOF index could be used as a noninvasive quantitative marker for the preclinical stage of AD.

Functional magnetic resonance imaging: emerging clinical applications

Functional magnetic resonance imaging (fMRI) is a relatively new and noninvasive method of functional brain mapping. Functional MRI is increasingly being applied to the study of neuropsychiatric disorders, including schizophrenia, Alzheimer's disease, traumatic brain injury, and others. Particularly noteworthy are findings related to plasticity in the adult human brain. Despite the promise of fMRI for improving the conceptualization, assessment, and treatment of neuropsychiatric disorders, important technical and scientific issues remain. Future research will address integrating fMRI with other emerging neuroimaging techniques.

Clinical pharmacokinetics and pharmacodynamics of cholinesterase inhibitors

Cholinesterase inhibitors are the 'first-line' agents in the treatment of Alzheimer's disease. This article presents the latest information on their pharmacokinetic properties and pharmacodynamic activity. Tacrine was the first cholinesterase inhibitor approved by regulatory agencies, followed by donepezil, rivastigmine and recently galantamine. With the exception of low doses of tacrine, the cholinesterase inhibitors exhibit a linear relationship between dose and area under the plasma concentration-time curve. Cholinesterase inhibitors are rapidly absorbed through the gastrointestinal tract, with time to peak concentration usually less than 2 hours; donepezil has the longest absorption time of 3 to 5 hours. Donepezil and tacrine are highly protein bound, whereas protein binding of rivastigmine and galantamine is less than 40%. Tacrine is metabolised by hepatic cytochrome P450 (CYP) 1A2, and donepezil and galantamine are metabolised by CYP3A4 and CYP2D6. Rivastigmine is metabolised by sulfate conjugation. Two cholinesterase enzymes are present in the body, acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). Tacrine and rivastigmine inhibit both enzymes, whereas donepezil and galantamine specifically inhibit AChE. Galantamine also modulates nicotine receptors, thereby enhancing acetylcholinergic activity at the synapse. These different pharmacological profiles provide distinctions between these agents. Cholinesterase inhibitors show a nonlinear relationship between dose and cholinesterase inhibition, where a plateau effect occurs. Cholinesterase inhibitors display a different profile as each agent achieves its plateau at different doses. In clinical trials, cholinesterase inhibitors demonstrate a dose-dependent effect on cognition and functional activities. Improvement in behavioural symptoms also occurs, but without a dose-response relationship. Gastrointestinal adverse events are dose-related. Clinical improvement occurs with between 40 and 70% inhibition of cholinesterase. A conceptual model for cholinesterase inhibitors has been proposed, linking enzyme inhibition, clinical efficacy and adverse effects. Currently, measurement of enzyme inhibition is used as the biomarker for cholinesterase inhibitors. New approaches to determining the efficacy of cholinesterase inhibitors in the brain could involve the use of various imaging techniques. The knowledge base for the pharmacokinetics and pharmacodynamics of cholinesterase inhibitors continues to expand. The increased information available to clinicians can optimise the use of these agents in the management of patients with Alzheimer's disease.

Compromised hemodynamic response in amyloid precursor protein transgenic mice

APP23 transgenic mice overexpressing amyloid precursor protein (APP751) reproduce neuropathological changes associated with Alzheimer's disease such as high levels of amyloid plaques, cerebral amyloid angiopathy, and associated vascular pathologies. Functional magnetic resonance imaging (fMRI) was applied to characterize brain functionality in these mice through global pharmacological stimulation. The cerebral hemodynamic response to infusion of the GABA(A) antagonist bicuculline was significantly reduced in aged APP23 mice compared with age-matched wild-type littermates. This is in part attributable to a compromised cerebrovascular reactivity, as revealed by the reduced responsiveness to vasodilatory stimulation by acetazolamide. The study shows that fMRI is a sensitive tool to phenotype genetically engineered animals modeling neuropathologies.

Cholinergic nicotinic systems in Alzheimer's disease: prospects for pharmacological intervention

Within the last few years, research into the cause and progression of Alzheimer's disease has made significant advances. Although there is still no preventative treatment or cure for this neurodegenerative illness, the development of drugs that may alleviate some of the cognitive symptoms associated with it is advancing. Cholinesterase inhibitors are at present the most effective form of treatment and have shown significant overall response rates in clinical trials. However, although some patients show substantial improvement when treated with this class of drugs, there is considerable variability in the amount of benefit gained in different individuals in terms of their cognitive and behavioural functioning. Furthermore, unfortunately some patients gain little or no benefit from these drugs. It would therefore be of great advantage to explore alternative therapeutic possibilities. This article reviews the potential involvement of the nicotinic cholinergic system in Alzheimer's disease and discusses the possibility of nicotinic pharmacotherapy. Substantial evidence indicates the involvement of the nicotinic cholinergic system in the pathology of Alzheimer's disease. Drugs targeting these sites may not only have a positive effect on cognitive function, but also have additional therapeutic benefits in terms of restoring the hypoactivity in the excitatory amino acid pyramidal system and even slowing the emergence of Alzheimer's disease pathology. The conclusion of this review is that nicotinic treatments are an important potential source of new therapeutic interventions in Alzheimer's disease.

Mild cognitive impairment

Mild cognitive impairment is an emerging term that encompasses the clinical state between elderly normal cognition and dementia. Controversy surrounds its characterization, implementation, and definition. Mild cognitive impairment is now the focus of natural history studies, biomarker studies, along with Alzheimer's disease prevention studies. The mild cognitive impairment stage may be the optimum stage at which to intervene with preventive therapies. Depending on the cohort source and definition, between 19 and 50% of mild cognitive impairment individuals progress to dementia (usually Alzheimer's disease) over 3 years. Despite controversy, progress has been achieved in defining risk factors for progression from mild cognitive impairment to dementia. New treatments to prevent development of Alzheimer's disease are targeting mild cognitive impairment as a treatment group and neurologists will increasingly be called upon to make this diagnosis.

Brain-imaging surrogate markers for detection and prevention of age-related memory loss

Recent evidence points to the importance of neuropathological and cognitive changes preceding Alzheimer's disease (AD), and clinical trials have begun to focus on preventive treatments designed to slow age-related cognitive decline and delay the onset of AD in people with age-associated memory impairment (AAMI). Studying subjects with few deficits leads to diagnostic heterogeneity and a need for larger samples in order to detect active drug effects. In this report, I review results of recent studies designed to address such issues. Middle-aged and older adults with mild memory complaints were studied using brain imaging and measures of the major known genetic risk for AD, the apolipoprotein E-4 (APOE-4) allele. In a study of positron emission tomography during mental rest, glucose metabolic rates were significantly lower in APOE-4 carriers in brain regions affected by AD. Another study using functional magnetic resonance imaging showed increased brain activation during memory tasks in APOE-4 carriers in similar brain regions. Longitudinal follow-up after 2 yr indicated the potential utility of such brain-imaging measures, combined with genetic-risk information, as surrogate markers in treatment trials for AAMI to prevent further cognitive decline. Current development focuses on novel technologies using positron emission tomography to directly image the neuritic plaques and neurofibrillary tangles of AD in order to provide more specific measures of disease progression in future clinical trials.

Functional reorganisation of memory after traumatic brain injury: a study with H(2)(15)0 positron emission tomography

OBJECTIVE

To study the effects of moderate to severe traumatic brain injury (TBI) on the functional neuroanatomy supporting memory retrieval.

METHODS

Subjects were six patients who had sustained a moderate to severe TBI about four years before scanning and had since made a good recovery. Eleven healthy young adults matched to the patients for age and education served as controls. An established H(2)(15)0 positron emission tomography paradigm was used to elicit brain activations in response to memory retrieval. TBI patients' patterns of brain activation were compared statistically with those of control subjects. Both group and individual case data were analysed.

RESULTS

Both TBI patients and controls engaged frontal, temporal, and parietal regions known to be involved in memory retrieval, yet the TBI patients showed relative increases in frontal, anterior cingulate, and occipital activity. The hemispheric asymmetry characteristic of controls was attenuated in patients with TBI. Reduced activation was noted in the right dorsomedial thalamus. Although local aspects of this pattern were affected by the presence of focal lesions and performance differences, the overall pattern was reliable across patients and comparable to functional neuroimaging results reported for normal aging, Alzheimer's disease, and other patients with TBI.

CONCLUSIONS

The TBI patients performed memory tasks using altered functional neuroanatomical networks. These changes are probably the result of diffuse axonal injury and may reflect either cortical disinhibition attributable to disconnection or compensation for inefficient mnemonic processes.

Achieving and maintaining cognitive vitality with aging

Cognitive vitality is essential to quality of life and survival in old age. With normal aging, cognitive changes such as slowed speed of processing are common, but there is substantial interindividual variability, and cognitive decline is clearly not inevitable. In this review, we focus on recent research investigating the association of various lifestyle factors and medical comorbidities with cognitive aging. Most of these factors are potentially modifiable or manageable, and some are protective. For example, animal and human studies suggest that lifelong learning, mental and physical exercise, continuing social engagement, stress reduction, and proper nutrition may be important factors in promoting cognitive vitality in aging. Manageable medical comorbidities, such as diabetes, hypertension, and hyperlipidemia, also contribute to cognitive decline in older persons. Other comorbidities such as smoking and excess alcohol intake may contribute to cognitive decline, and avoiding these activities may promote cognitive vitality in aging. Various therapeutics, including cognitive enhancers and protective agents such as antioxidants and anti-inflammatories, may eventually prove useful as adjuncts for the prevention and treatment of cognitive decline with aging. The data presented in this review should interest physicians who provide preventive care management to middle-aged and older individuals who seek to maintain cognitive vitality with aging.

Presenile dementia syndromes: an update on taxonomy and diagnosis

The four major degenerative dementias that often begin in presenescence: are reviewed. These are Alzheimer's disease, frontotemporal dementia, dementia with Lewy bodies, and Creutzfeldt-Jakob disease. Their epidemiological, genetic, and clinical features are reviewed, and controversies in taxonomy arising from recent discoveries described. Particular attention is given to the pathological role of protein aggregation, which appears to be a factor in each disease.

Neuroimaging to predict preclinical Alzheimer's disease

Alzheimer's disease is common in the elderly and causes tremendous distress to patients and their carers. With the advent of newer pharmacological treatments, significant improvement in the early diagnosis of Alzheimer's disease is required. This article examines the usefulness of neuroimaging techniques to predict Alzheimer's disease in prediagnosis individuals.

Hippocampal atrophy in persons with age-associated memory impairment: volumetry within a common space

OBJECTIVE

The objective of this study is to demonstrate the assessment of hippocampal atrophy within a standard brain atlas for persons with age-associated memory impairment (AAMI) compared with cognitively intact elderly.

METHODS

High-resolution three-dimensional (3D) brain magnetic resonance imaging (MRI) was performed on 20 nondemented persons: 10 had AAMI and 10 were normal elderly. Scans were aligned to a common atlas template to control for errors due to variable brain size and orientation as well as facilitating communication of results across centers. Manual outlining every 1 mm with volumes determined for both the hippocampal head and body was accomplished after coronal resampling perpendicular to the long axis of the hippocampus.

RESULTS

Subject groups were similar in age, sex ratios, and educational achievement. The AAMI group had significantly lower volumes for the right hippocampus and hippocampal head (p =.02) compared with controls.

CONCLUSION

A growing body of work suggests the right hippocampal head as an early site of atrophy in early memory impairment. Subtle atrophic changes are detectable within a common atlas template allowing imaging assessment across centers.

Technical aspects and utility of fMRI using BOLD and ASL

Functional magnetic resonance imaging (fMRI) is an emerging methodology which provides various approaches to visualizing regional brain activity non-invasively. Although the exact mechanisms underlying the coupling between neural function and fMRI signal changes remain unclear, fMRI studies have been successful in confirming task-specific activation in a variety of brain regions, providing converging evidence for functional localization. In particular, fMRI methods based on blood oxygenation level dependent (BOLD) contrast and arterial spin labeling (ASL) perfusion contrast have enabled imaging of changes in blood oxygenation and cerebral blood flow (CBF). While BOLD contrast has been widely used as the surrogate marker for neural activation and can provide reliable information on the neuroanatomy underlying transient sensorimotor and cognitive functions, recent evidence suggests perfusion contrast is suitable for studying relatively long term effects on CBF both at rest or during activation. New developments in combining or simultaneously measuring the electrophysiological and fMRI signals allow a new class of studies that capitalize on dynamic imaging with high spatiotemporal resolution. This article reviews the biophysical bases and methodologies of fMRI and its applications to the clinical neurosciences, with emphasis on the spatiotemporal resolution of fMRI and its coupling with neurophysiology under both normal and pathophysiological conditions.

Women at risk for AD show increased parietal activation during a fluency task

BACKGROUND

Imaging studies have shown disparities in resting metabolism and in functional activation between cognitively normal individuals at high and low risk for AD. A recent study has shown increased parietal activation in high-risk subjects during a paired associates recall task, which the authors postulated might overlap activation typically observed in verbal fluency.

OBJECTIVE

To determine whether parietal activation is altered in a letter fluency task in cognitively normal individuals at high risk for AD.

METHODS

fMRI was used to compare cortical activation between two groups of cognitively normal women differing in their risk for developing AD. A letter fluency task was used, which activates left frontal and parietal regions. The risk groups differed in family history of AD and APOE allele status but were matched in age, education, and measures of cognitive performance. Average age of the study participants was 53 years.

RESULTS

The regional patterns of brain activation were similar between groups and similar to patterns observed by other investigators. However, the high-risk group showed significantly increased activation in the left parietal region despite identical letter fluency performance between risk groups.

CONCLUSIONS

Cognitively normal individuals at high risk for AD show increased brain activation in the left parietal region with letter fluency, a region adjacent to that observed by others using a recall task. This convergence of results indicates disruption of functional circuits involving the left parietal lobe in asymptomatic individuals at increased risk for AD.

Functional neuroimaging in neurology and psychiatry

How can functional neuroimaging be applied to clinical neurology and psychiatry? This article reviews selected contributions of functional neuroimaging to the clinical neurosciences. We review selected technical aspects of positron emission tomography, single photon emission tomography, and functional magnetic resonance imaging with a focus on the relative strengths and weaknesses of these techniques. Consumers of functional neuroimaging research are encouraged to consider the limitations of imaging techniques and theoretical pitfalls of cognitive task design when interpreting results of functional imaging studies. Then, we selectively review the contributions of functional neuroimaging to neurology and psychiatry, including the areas of epilepsy, stroke, chronic pain, schizophrenia, depression, and obsessive-compulsive disorder. Future directions of functional neuroimaging research are offered, with the emphasis that the best conclusions are informed by a convergence of research from functional neuroimaging, neurophysiological, and lesion studies.

Subjective memory complaints: objective neural markers in patients with Alzheimer's disease and major depressive disorder

Patients with probable Alzheimer's disease and depressive patients frequently present with subjective memory complaints. Objective distinction of underlying neuronal substrate malfunction and early cross-sectional differential diagnosis have been elusive thus far. We used repetitive learning and free recall of abstract geometric patterns during functional magnetic resonance imaging to assess episodic memory in older subjects (ages 56-64 years) who sought first-time medical attention with subjective memory complaints and were diagnosed with probable Alzheimer's disease (NINCDS-ADRDA criteria; ages 51-67 years) or major depressive disorder (DSM-IV; ages 50-65 years). Contrasting healthy seniors or depressive patients with Alzheimer's disease patients revealed superiority of hippocampal activation. Contrasting Alzheimer's disease patients with seniors showed bilateral prefrontal activity as a correlate of futile compensation of episodic memory failure. Contrasting patients who had major depressive disorder with seniors or patients who had Alzheimer's disease showed bilateral activation of the orbitofrontal cortex and the anterior cingulate. Subjective memory complaints may be classified objectively and very early with functional magnetic resonance imaging of episodic memory in groups of patients with Alzheimer's disease and depressive syndrome. This may facilitate drug trials with evaluation of specific treatments, but further studies will be needed to establish the differential diagnosis for the individual patient.

The apolipoprotein E gene, attention, and brain function

The epsilon4 allele of the apolipoprotein E (ApoE) gene is associated with alterations in brain function and is a risk factor for Alzheimer's disease (AD). Changes in components of visuospatial attention with ApoE-epsilon4, aging, and AD are described. Healthy middle-aged adults without dementia who have the ApoE-epsilon4 gene show deficits in spatial attention and working memory that are qualitatively similar to those seen in clinically diagnosed AD patients. The findings support an association between ApoE polymorphism and specific components of visuospatial attention. Molecular mechanisms that may mediate the ApoE-attention link by modulating cholinergic neurotransmission to the posterior parietal cortex are discussed. Studies of attention and brain function in ApoE-epsilon4 carriers without dementia can advance knowledge of the genetics of visual attention, may enhance understanding of the preclinical phase of AD, and may lead to better methods for early AD detection.

Comparison of detrending methods for optimal fMRI preprocessing

Because of the inherently low signal to noise ratio (SNR) of fMRI data, removal of low frequency signal intensity drift is an important preprocessing step, particularly in those brain regions that weakly activate. Two known sources of drift are noise from the MR scanner and aliasing of physiological pulsations. However, the amount and direction of drift is difficult to predict, even between neighboring voxels. Further, there is no concensus on an optimal baseline drift removal algorithm. In this paper, five voxel-based detrending techniques were compared to each other and an auto-detrending algorithm, which automatically selected the optimal method for a given voxel time-series. For a significance level of P < 10(-6), linear and quadratic detrending moderately increased the percentage of activated voxels. Cubic detrending decreased activation, while a wavelet approach increased or decreased activation, depending on the dataset. Spline detrending was the best single algorithm. However, auto-detrending (selecting the best algorithm or none, if detrending is not useful) appears to be the most judicious choice, particularly for analyzing fMRI data with weak activations in the presence of baseline drift.