Age-related changes in brain: I. Magnetic resonance imaging measures of temporal lobe volumes in normal subjects

Genetic association between epigenetic aging-acceleration and the progression of mild cognitive impairment to Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder and previous studies have showed its association with accelerated aging. In this study, we hypothesized that SNPs that contributed to aging acceleration are also associated with the progression from mild cognitive impairment (MCI) to AD. By applying genetic correlation analysis and single-locus survival analysis, we investigated the associations between intrinsic- and extrinsic-epigenetic-age-acceleration (IEAA and EEAA) related SNPs and the progression time from mild cognitive impairment (MCI) to AD dementia using the data of 767 MCI participants from the ADNI study and 1373 MCI patients from the NACC study. Genetic correlations were found between IEAA/EEAA and AD (positive for IEAA-AD and negative for EEAA-AD). We revealed that 70 IEAA and 81 EEAA SNPs had associations with the progression time from MCI to AD with Bayesian false-discovery probability (BFDP) ≤ 0.8 in the ADNI study, with 22 IEAA SNPs and 16 EEAA SNPs being replicated in the NACC study (P < 0.05). Polygenic risk score (PRS) analysis showed that EEAA PRS but not IEAA PRS was associated with AD progression and the trend of decreasing Fusiform gyrus volume in two datasets. Risk models incorporating both EAA PRSs did not show any significant improvement in predictive accuracy. Our results identified multiple genetic variants with pleiotropic effects on both EAA and AD, which suggested shared genetic architecture between epigenetic age acceleration and AD progression.

Network curvature as a hallmark of brain structural connectivity

Although brain functionality is often remarkably robust to lesions and other insults, it may be fragile when these take place in specific locations. Previous attempts to quantify robustness and fragility sought to understand how the functional connectivity of brain networks is affected by structural changes, using either model-based predictions or empirical studies of the effects of lesions. We advance a geometric viewpoint relying on a notion of network curvature, the so-called Ollivier-Ricci curvature. This approach has been proposed to assess financial market robustness and to differentiate biological networks of cancer cells from healthy ones. Here, we apply curvature-based measures to brain structural networks to identify robust and fragile brain regions in healthy subjects. We show that curvature can also be used to track changes in brain connectivity related to age and autism spectrum disorder (ASD), and we obtain results that are in agreement with previous MRI studies.

The brain can often continue to function despite lesions in many areas, but damage to particular locations may have serious effects. Here, the authors use the concept of Ollivier-Ricci curvature to investigate the robustness of brain networks.

Adaptation of brain functional and structural networks in aging

The human brain, especially the prefrontal cortex (PFC), is functionally and anatomically reorganized in order to adapt to neuronal challenges in aging. This study employed structural MRI, resting-state fMRI (rs-fMRI), and high angular resolution diffusion imaging (HARDI), and examined the functional and structural reorganization of the PFC in aging using a Chinese sample of 173 subjects aged from 21 years and above. We found age-related increases in the structural connectivity between the PFC and posterior brain regions. Such findings were partially mediated by age-related increases in the structural connectivity of the occipital lobe within the posterior brain. Based on our findings, it is thought that the PFC reorganization in aging could be partly due to the adaptation to age-related changes in the structural reorganization of the posterior brain. This thus supports the idea derived from task-based fMRI that the PFC reorganization in aging may be adapted to the need of compensation for resolving less distinctive stimulus information from the posterior brain regions. In addition, we found that the structural connectivity of the PFC with the temporal lobe was fully mediated by the temporal cortical thickness, suggesting that the brain morphology plays an important role in the functional and structural reorganization with aging.

The limbic degradation of aging brain: a quantitative analysis with diffusion tensor imaging

Introduction. The limbic system primarily responsible for our emotional life and memories is known to undergo degradation with aging and diffusion tensor imaging (DTI) is capable of revealing the white matter integrity. The aim of this study is to investigate age-related changes of quantitative diffusivity parameters and fiber characteristics on limbic system in healthy volunteers. Methods. 31 healthy subjects aged 25–70 years were examined at 1,5 TMR. Quantitative fiber tracking was performed of fornix, cingulum, and the parahippocampal gyrus. The fractional anisotropy (FA) and apparent diffusion coefficient (ADC) measurements of bilateral hippocampus, amygdala, fornix, cingulum, and parahippocampal gyrus were obtained as related components. Results. The FA values of left hippocampus, bilateral parahippocampal gyrus, and fornix showed negative correlations with aging. The ADC values of right amygdala and left cingulum interestingly showed negative relation and the left hippocampus represented positive relation with age. The cingulum showed no correlation. The significant relative changes per decade of age were found in the cingulum and parahippocampal gyrus FA measurements. Conclusion. Our approach shows that aging affects hippocampus, parahippocampus, and fornix significantly but not cingulum. These findings reveal age-related changes of limbic system in normal population that may contribute to future DTI studies.

Senescent-induced dysregulation of cAMP/CREB signaling and correlations with cognitive decline

It is well known that alongside senescence there is a gradual decline in cognitive ability, most noticeably certain kinds of memory such as working, episodic, spatial, and long term memory. However, until recently, not much has been known regarding the specific mechanisms responsible for the decline in cognitive ability with age. Over the past decades, researchers have become more interested in cAMP signaling, and its downstream transcription factor cAMP response element binding protein (CREB) in the context of senescence. However, there is still a lack of understanding on what ultimately causes the cognitive deficits observed with senescence. This review will focus on the changes in intracellular signaling in the brain, more specifically, alterations in cAMP/CREB signaling in aging. In addition, the downstream effects of altered cAMP signaling on cognitive ability with age will be further discussed. Overall, understanding the senescent-related changes that occur in cAMP/CREB signaling could be important for the development of novel drug targets for both healthy aging, and pathological aging such as Alzheimer's disease.

Hippocampal blood flow in normal aging measured with arterial spin labeling at 3T

Due to methodological difficulties related to the small size, variable distribution of hippocampal arteries, and the location of the hippocampus in the proximity of middle cranial fossa, little is known about hippocampal blood flow (HBF). We have tested the utility of a pulsed arterial spin labeling sequence based on multi-shot true fast imaging in steady precession to measure HBF in 34 normal volunteers (17 women, 17 men, 26-92 years old). Flow sensitivity to a mild hypercapnic challenge was also examined. Coregistered 3D MPRAGE sequence was used to eliminate from hippocampal and cortical regions of interest all voxel with <75% of gray matter. Large blood vessels were also excluded. HBF in normal volunteers averaged 61.2 ± 9.0 mL/(100 g min). There was no statistically significant age or gender effect. Under a mild hypercapnia challenge (end tidal CO(2) pressure increase of 6.8 ± 1.9 mmHg over the baseline), HBF response was 14.1 ± 10.8 mL/(100 g min), whereas cortical gray matter flow increased by 18.0 ± 12.2 mL/(100 g min). Flow response among women was significantly larger than in the men. The average absolute difference between two successive HBF measures was 3.6 mL/(100 g min) or 5.4%. The 3T true fast imaging in steady precession arterial spin labeling method offers a HBF measurement strategy that combines good spatial resolution, sensitivity, and minimal image distortions.

Age-related changes of elements and relationships among elements in human hippocampus, dentate gyrus, and fornix

To elucidate compositional changes of the limbic system with aging, the authors investigated age-related changes of elements in the hippocampus, dentate gyrus, and fornix and the relationships among elements by direct chemical analysis. After ordinary dissections at Nara Medical University were finished, the hippocampi, dentate gyri, and fornices were resected from identical cerebra of the subjects which consisted of 23 men and 23 women, ranging in age from 70 to 101 years. After ashing with nitric acid and perchloric acid, element contents were determined by inductively coupled plasma-atomic emission spectrometry. The average contents of P, Zn, and Na were significantly less in both the hippocampi and dentate gyri compared with the fornices. It was found that the Ca and Mg contents increased significantly in the hippocampus with aging; the P content increased significantly in the dentate gyrus with aging, whereas the Na content decreased in the dentate gyrus with aging; and the Mg content increased significantly in the fornix with aging. Regarding the relationships among elements, a significant direct correlation between Ca and Fe contents and an extremely significant inverse correlation between P and Zn contents were found in both the hippocampi and dentate gyri. In addition, a significant direct correlation between P and Mg contents was found in both the hippocampi and fornices. Pearson's correlation was used to examine whether there were elements with significant correlation among the hippocampus, dentate gyrus, fornix, and mammillary body. Significant correlations were found in five elements of Ca, P, Mg, Zn, and Fe except for S and Na among the hippocampus, dentate gyrus, and mammillary body with one exception. Regarding the fornix, significant correlations were found in two elements of P and Fe between the fornix and hippocampus, dentate gyrus, or mammillary body.

Involvement of BDNF in age-dependent alterations in the hippocampus

It is known since a long time that the hippocampus is sensitive to aging. Thus, there is a reduction in the hippocampal volume during aging. This age-related volume reduction is paralleled by behavioral and functional deficits in hippocampus-dependent learning and memory tasks. This age-related volume reduction of the hippocampus is not a consequence of an age-related loss of hippocampal neurons. The morphological changes associated with aging include reductions in the branching pattern of dendrites, as well as reductions in spine densities, reductions in the densities of fibers projecting into the hippocampus as well as declines in the rate of neurogenesis. It is very unlikely that a single factor or a single class of molecules is responsible for all these age-related morphological changes in the hippocampus. Nevertheless, it would be of advantage to identify possible neuromodulators or neuropeptides that may contribute to these age-related changes. In this context, growth factors may play an important role in the maintenance of the postnatal hippocampal architecture. In this review it is hypothesized that brain-derived neurotrophic factor (BDNF) is a factor critically involved in the regulation of age-related processes in the hippocampus. Moreover, evidences suggest that disturbances in the BDNF-system also affect hippocampal dysfunctions, as e.g. seen in major depression or in Alzheimer disease.

Quantitative and qualitative measures of hippocampal atrophy are not correlated in healthy older men

BACKGROUND AND PURPOSE

In neuroimaging studies of dementia and mild cognitive impairment, hippocampal atrophy (HA) is commonly assessed by qualitative ratings of hippocampal appearance, or by measuring hippocampal volumes. These estimates of HA are considered to be equivalent. However, few studies have examined their relationship, especially in healthy older individuals. We therefore examined the relationship between hippocampal qualitative atrophy scores and quantitative volumetric measurements in healthy older men.

METHODS

Ninety-seven healthy community-dwelling 65-70-year-old men underwent magnetic resonance imaging scanning. Hippocampal volumes were measured and adjusted for intracranial size. A validated 4-point visual rating scale was used to assess hippocampal atrophy.

RESULTS

There was a wide range of unadjusted hippocampal volumes among subjects (right: 2,582 to 5,196 mm(3)[mean 3,626 mm(3); SD 465.5 mm(3)] and left: 2,111 to 4,580 mm(3)[mean 3,501 mm(3); SD 439.5 mm(3)]), which was maintained following adjustment for intracranial size. However, only 9% of subjects were rated as having moderate or severe HA. Qualitative and quantitative measures were not significantly correlated (left hippocampus: rho = .07, P= .52; right hippocampus: rho = .10, P= .34).

CONCLUSIONS

This study shows that qualitative and quantitative indices of hippocampal atrophy in healthy older men are not equivalent. Small hippocampal volumes do not necessarily equate to hippocampal atrophy.

Differential effects of normal aging on memory for odor-place and object-place associations

Odor-place and object-place associative memory were compared in healthy older (over the age of 65) and young (18 to 25 years of age) adults. Twelve spatial locations were defined on a tabletop board. Either six odors or six objects were presented one at a time and each was paired with a location on the board. The participant then was presented with each stimulus individually and asked to place it in its paired location. Older adults showed impaired odor-place associative memory but unimpaired object-place memory compared to young adults. Item recognition memory for the individual stimuli or locations used on the associative memory task was similar in both groups. The results suggest that odor-place associative memory is particularly affected by age-related brain changes.

Medial temporal lobe atrophy in vascular dementia: visual temporal lobe rating scale

Medial temporal lobe atrophy (MTA) as assessed by magnetic resonance imaging (MRI) can be measured in several ways. First of all, visual rating scale is a quick and easy measurement. MTA is a sensitive marker for Alzheimer's disease (AD), but not specific. It has been documented in other dementias including vascular dementia (VD). This study is to evaluate the degree of MTA in VD patients using a standardized visual rating scale and to suggest the importance of the possible role of MTA in VD. Twenty-five VD, 33 AD and 27 non-demented patients underwent a coronal three-dimensional magnetization prepared rapid gradient echo brain MRI sequence. MTA was rated visually using a 5-point rating scale from 0 (no atrophy) to 4 (severe atrophy). The mean summed MTA score was 5.39 in AD, 2.16 in VD and 0.56 in non-demented patients. Most of the VD patients (80%) showed MTA. They were greater in bilateral sides compared with the non-demented group, but milder than in AD. Additionally, MTA of left side score was significantly associated with age. Medial temporal lobe volumes measured visually are smaller in size in patients with VD, although not to the same extent as in AD. This suggests that MTA in VD patients may be associated with pre-existing AD.

Age effects on hippocampal structural changes in old men: the HAAS

Understanding the variability of the hippocampus in human brain research is essential. The effect of age on the hippocampus has been explored in several studies that have been focused on either normal aging or neural degeneration. Shape analysis of magnetic resonance imaging (MRI) provides morphological measures for brain structures. This study further investigates the age effects on hippocampal morphology in three groups (104 normal controls, 24 Alzheimer's disease (AD) and 14 vascular dementia (VaD) patients). By utilizing a parametric shape analysis of hippocampal MRI scans, each individual distance map is generated and analyzed statistically. Specifically, after eliminating similarity parameters (rotation, translation, and scaling) effects for each hippocampus, an individual distance map is generated from parametric hippocampal surfaces and medial axes. Then statistical methods, including regression, and permutation tests, are applied to detect the differences in hippocampal distance maps and volumes under the effect of age in each group. Statistical analyses reveal that the loss of hippocampal volume and changes in shape are more significantly related to aging in the control group than in AD/VaD. The results also show that the asymmetry of hippocampus in healthy subjects is greater than that in either of the disease groups. Our study shows that 3D statistical shape analysis could enhance the understanding of age effects on local areas of hippocampi. However, the sample sizes of disease groups are relatively low; further studies with more AD/VaD data are needed.

Quantitative diffusion tensor fiber tracking of age-related changes in the limbic system

Cerebral white matter is known to undergo degradation with aging, and diffusion tensor imaging (DTI) is capable of revealing the white matter integrity. We assessed age-related changes of quantitative diffusivity parameters and fiber characteristics within the fornix and the cingulum. Thirty-eight healthy subjects aged 18-88 years were examined at 3 Tesla using a 1.9-mm isotropic DTI sequence. Quantitative fiber tracking was performed for 3D-segmentation of the fornix and the cingulum to determine fractional anisotropy (FA), mean diffusivity (MD), eigenvalues (lambda1, lambda2, and lambda3), number of fibers (NoF), and mean NoF/voxel (FpV). In the fornix, all diffusivity parameters (FA, MD, and eigenvalues) were moderately correlated with age. Strong and moderate negative correlations for NoF and FpV were found, respectively. In the cingulum, no correlation was observed between FA and age, and only weak correlations for the other quantitative parameters. Differences in correlations between the fornix and the cingulum were significant for all diffusivity parameters and for NoF, but not for FpV. The strongest relative changes per decade of age were found in the fornix: FA -2.1%, MD 4.2%, NoF -10.6%, and FpV -4.6%. Our quantitative 3D fiber tracking approach shows that the cingulum is resistant to aging while the fornix is not.

The effects of stress and stress hormones on human cognition: Implications for the field of brain and cognition

In this review, we report on studies that have assessed the effects of exogenous and endogenous increases in stress hormones on human cognitive performance. We first describe the history of the studies on the effects of using exogenous stress hormones such as glucocorticoids as anti-inflammatory medications on human cognition and mental health. Here, we summarize the cases that led to the diagnosis of glucocorticoid-induced 'steroid psychosis' in human populations and which demonstrated that these stress hormones could thus cross the blood-brain barrier and access the brain where they could influence cognition and mental health. We then summarize studies that assessed the effects of the exogenous administration of glucocorticoids on cognitive performance supported by the hippocampus, the frontal lobes and amygdala. In the second section of the paper, we summarize the effects of the endogenous release of glucocorticoids induced by exposure to a stressful situation on human cognition and we further dissociate the effects of emotion from those of stress on human learning and memory. Finally, in the last section of the paper, we discuss the potential impact that the environmental context to which we expose participants when assessing their memory could have on their reactivity to stress and subsequent cognitive performance. In order to make our point, we discuss the field of memory and aging and we suggest that some of the 'age-related memory impairments' observed in the literature could be partly due to increased stress reactivity in older adults to the environmental context of testing. We also discuss the inverse negative correlations reported between hippocampal volume and memory for young and older adults and suggest that these inverse correlations could be partly due to the effects of contextual stress in young and older adults, as a function of age-related differences in hippocampal volume.

An evaluation of distinct volumetric and functional MRI contributions toward understanding age and task performance: a study in the basal ganglia

Prior work by our group and others has implicated the basal ganglia as important in age-related differences in tasks involving motor response control. The present study used structural and functional MRI approaches to analyze this region of interest (ROI) toward better understanding the contributions of structural and functional MRI measures to understanding age-related and task performance-related cognitive differences. Eleven healthy elders were compared with 11 healthy younger adults while they completed the "go" portion of a complex Go/No-go task. Separate ROI's in the bilateral caudate (C) and putamen/globus pallidus (PGp) were studied based upon previous findings of age-related functional MRI differences in basal ganglia for this portion of the task. Structural volumes and functional activation (in percent area under the curve during correct responses) were independently extracted for these ROI's. Results showed that age correlated with ROI volume in bilateral PGp and C, while multiple task performance measures correlated with functional activation in the left PGp. The Go/No-go task measures were also significantly correlated with traditional attention and executive functioning measures. Importantly, fMRI activation and volumes from each ROI were not significantly inter-correlated. These findings suggest that structural and functional MRI make unique contributions to the study of performance changes in aging.

Aging, gender, and the elderly adult brain: an examination of analytical strategies

We sought to examine the relations between age, gender and brain volumes in an elderly population; we also sought to examine ways of measuring these relations. Three sets of analyses were used: correlational analyses, in which correlations between independent variables and brain volumes were calculated without correction for intracranial volume (ICV); covariational analyses, in which ICV was used as a covariate in regression equations; and ratio analyses, in which the dependent variable was the ratio of brain volume to ICV. These analyses yielded similar results, except that (as expected) adjusting for ICV altered estimates of gender differences. Analyses of age showed decreases in left caudate, putamen, and right hippocampus and an increase in CSF, a result generally in accord with previous findings. However, we also found a significant decrease of white-matter volumes and no significant decrease in total gray-matter volumes. Correlational analyses showed that men did not always have larger volumes despite their larger head size; women generally had larger volumes after adjusting for ICV. We found no age-gender interactions.

MR-based in vivo hippocampal volumetrics: 2. Findings in neuropsychiatric disorders

Magnetic resonance imaging (MRI) has opened a new window to the brain. Measuring hippocampal volume with MRI has provided important information about several neuropsychiatric disorders. We reviewed the literature and selected all English-language, human subject, data-driven papers on hippocampal volumetry, yielding a database of 423 records. Smaller hippocampal volumes have been reported in epilepsy, Alzheimer's disease, dementia, mild cognitive impairment, the aged, traumatic brain injury, cardiac arrest, Parkinson's disease, Huntington's disease, Cushing's disease, herpes simplex encephalitis, Turner's syndrome, Down's syndrome, survivors of low birth weight, schizophrenia, major depression, posttraumatic stress disorder, chronic alcoholism, borderline personality disorder, obsessive-compulsive disorder, and antisocial personality disorder. Significantly larger hippocampal volumes have been correlated with autism and children with fragile X syndrome. Preservation of hippocampal volume has been reported in congenital hyperplasia, children with fetal alcohol syndrome, anorexia nervosa, attention-deficit and hyperactivity disorder, bipolar disorder, and panic disorder. Possible mechanisms of hippocampal volume loss in neuropsychiatric disorders are discussed.

Protocol for volumetric segmentation of medial temporal structures using high-resolution 3-D magnetic resonance imaging

Quantitative analysis of brain structures in normal subjects and in different neurological conditions can be carried out in vivo through magnetic resonance imaging (MRI) volumetric studies. The use of high-resolution MRI combined with image post-processing that allows simultaneous multiplanar view may facilitate volumetric segmentation of temporal lobe structures. We define a protocol for volumetric studies of medial temporal lobe structures using high-resolution MR images and we studied 30 healthy subjects (19 women; mean age, 33 years; age range, 21-55 years). Images underwent field non-homogeneity correction and linear stereotaxic transformation into a standard space. Structures of interest comprised temporopolar, entorhinal, perirhinal, parahippocampal cortices, hippocampus, and the amygdala. Segmentation was carried out with multiplanar assessment. There was no statistically significant left/right-sided asymmetry concerning any structure analyzed. Neither gender nor age influenced the volumes obtained. The coefficient of repeatability showed no significant difference of intra- and interobserver measurements. Imaging post-processing and simultaneous multiplanar view of high-resolution MRI facilitates volumetric assessment of the medial portion of the temporal lobe with strict adherence to anatomic landmarks. This protocol shows no significant inter- and intraobserver variations and thus is reliable for longitudinal studies.

Regional Brain Atrophy Rate Predicts Future Cognitive Decline: 6-year Longitudinal MR Imaging Study of Normal Aging

PURPOSE

To determine if medial temporal lobe (MTL) atrophy rate, assessed by using an automated procedure over the initial time interval of a 6-year, three-time-point longitudinal study, is predictive of future memory decline.

MATERIALS AND METHODS

Healthy elderly subjects (age, >60 years) were administered a comprehensive battery of neuropsychometric tests and underwent magnetic resonance (MR) imaging at baseline and two or more follow-up examinations. The rate of brain atrophy between the baseline and first follow-up examinations was assessed by using an automated procedure that included spatial coregistration of the two images and regional brain boundary shift analysis. At final observation, the 45 subjects were separated into a group of those who did and a group of those who did not show objective evidence of cognitive decline. A forward stepwise logistic regression model was used to identify variables that predicted decline.

RESULTS

Thirty-two subjects remained healthy, and 13 showed cognitive decline. Among subjects who showed cognitive decline, six declined after the second observation. MTL atrophy rate, through its interactions with sex and age, was the most significant predictor of decline. The overall accuracy of prediction was 89% (in 40 of 45 subjects), with 91% specificity (in 29 of 32 subjects) and 85% sensitivity (in 11 of 13 subjects).

CONCLUSION

Among healthy elderly individuals, increased MTL atrophy rate appears to be predictive of future memory decline.

Reduced glucose tolerance is associated with poor memory performance and hippocampal atrophy among normal elderly

Poor glucose tolerance and memory deficits, short of dementia, often accompanies aging. The purpose of this study was to ascertain whether, among nondiabetic, nondemented middle-aged and elderly individuals, poorer glucose tolerance is associated with reductions in memory performance and smaller hippocampal volumes. We studied 30 subjects who were evaluated consecutively in an outpatient research setting. The composition of the participant group was 57% female and 68.6 +/- 7.5 years of age; the participants had an average education of 16.2 +/- 2.3 years, a score on the Mini Mental State Examination of 28.6 +/- 1.5, a glycosylated hemoglobin (HbA1C) of 5.88 +/- 0.74%, and a body mass index of 24.9 +/- 4.1 kg/m(2). Glucose tolerance was measured by an i.v. glucose tolerance test. Memory was tested by using the Wechsler Paragraphs recall tests at the time of administering the i.v. glucose tolerance test. The hippocampus and other brain volumes were measured by using validated methods on standardized MRIs. Decreased peripheral glucose regulation was associated with decreased general cognitive performance, memory impairments, and atrophy of the hippocampus, a brain area that is key for learning and memory. These associations were independent of age and Mini Mental State Examination scores. Therefore, these data suggest that metabolic substrate delivery may influence hippocampal structure and function. This observation may bring to light a mechanism for aging brain injury that may have substantial medical impact, given the large number of elderly individuals with impaired glucose metabolism.

Alzheimer's disease: its diagnosis and pathogenesis

A hypothesis has been presented that links many of the identified and putative risk factors for AD and suggests a mechanism for their action. Crawford (1996, 1998) proposes an association between AD and cerebral blood flow (CBF) by citing evidence that many of the factors that are linked with an increased risk of AD also decrease CBF (e.g., old age, depression, underactivity, head trauma). Similarly, it is suggested factors that increase CBF are associated with a decreased risk of AD (e.g., education, exercise, smoking, NSAIDs). Although the authors acknowledge that reduced CBF is not sufficient to cause AD, the reported positive and negative associations provide tantalizing evidence for a common mode of action for many of the equivocal risk factors reported to date. This hypothesis is also consistent with other data that links microvascular damage and impaired blood flow (de la Torre, 1997, 2000) and low education with increased cerebrovascular disease (Del Ser et al., 1999). Gaining a better understanding of the interaction between AD and vascular disease is of great importance. Not only will it provide insights into the pathogenesis of AD, but it may also provide us with a rare opportunity for the treatment and possible prevention of AD. A great many risk factors for vascular disease have been identified and intervention programs have successfully reduced the incidence of heart disease and stroke. The potential exists to provide the same level of success with AD.

Hippocampal formation glucose metabolism and volume losses in MCI and AD

We used MRI volume sampling with coregistered and atrophy corrected FDG-PET scans to test three hypotheses: 1) hippocampal formation measures are superior to temporal neocortical measures in the discrimination of normal (NL) and mild cognitive impairment (MCI); 2) neocortical measures are most useful in the separation of Alzheimer disease (AD) from NL or MCI; 3) measures of PET glucose metabolism (MRglu) have greater diagnostic sensitivity than MRI volume. Three groups of age, education, and gender matched NL, MCI, and AD subjects were studied. The results supported the hypotheses: 1) entorhinal cortex MRglu and hippocampal volume were most accurate in classifying NL and MCI; 2) both imaging modalities identified the temporal neocortex as best separating MCI and AD, whereas widespread changes accurately classified NL and AD; 3) In most between group comparisons regional MRglu measures were diagnostically superior to volume measures. These cross-sectional data show that in MCI hippocampal formation changes exist without significant neocortical changes. Neocortical changes best characterize AD. In both MCI and AD, metabolism reductions exceed volume losses.

Neuroanatomic substrates of late-life mental disorders

Advances in magnetic resonance imaging (MRI) techniques have made it possible to quantify anatomic brain abnormalities in neuropsychiatric disorders. This review focuses on controlled, quantitative MRI studies in depression, degenerative disorders, and psychosis in the elderly. Although many of the anatomic abnormalities detected are observed across disorders, the patterns of regional involvement may be more selective and disorder specific. We integrate MRI findings with relevant clinical and neurobiologic observations in an attempt to develop a cohesive model of late-life psychiatric illness. Although the model primarily alludes to the pathophysiology of late-life depression, it may have broader biologic implications for other mental disorders in the elderly.

Atrophy of the medial occipitotemporal, inferior, and middle temporal gyri in non-demented elderly predict decline to Alzheimer's disease

Our goal was to ascertain, among normal elderly and individuals with mild cognitive impairment, which temporal lobe neocortical regions predicted decline to dementia of the Alzheimer's type (DAT). Individuals received an MRI at baseline and a clinical and cognitive evaluation at baseline and follow-up. By using the baseline MRI we assessed the anatomical subdivisions of the temporal lobe: anteromedial temporal lobe (hippocampus and parahippocampal gyrus), medial occipitotemporal (fusiform) gyrus, middle and inferior temporal gyri, and superior temporal gyrus. We studied two groups of carefully screened age- and education-matched elderly individuals: 26 normal elderly (NL) and 20 individuals with mild cognitive impairment (MCI). Fourteen individuals (12 from the MCI group and two from the NL group) declined to DAT within the 3.2-year follow-up interval. We used logistic regression analyses to ascertain whether the baseline brain volumes were useful predictors of decline to DAT at follow-up after accounting for age, gender, individual differences in brain size, and other variables known to predict DAT. After accounting for age, gender, and head size, adding the volume of the anteromedial temporal lobe (the aggregate of hippocampus and parahippocampal gyrus) and an index of global atrophy raised the accuracy of overall classification to 80.4%. However, the ability to detect those individuals who declined (sensitivity) was low at 57%. When baseline medial occipitotemporal and the combined middle and inferior temporal gyri were added to the logistic model, the overall classification accuracy reached 95.6% and, most importantly, the sensitivity rose to 92.8%. These data indicate that the medial occipitotemporal and the combined middle and inferior temporal gyri may be the first temporal lobe neocortical sites affected in AD; atrophy in these areas may herald the presence of future AD among nondemented individuals. No other clinical baseline variables examined predicted decline with sensitivities above 71%. The apolipoprotein APOE epsilon4 genotype was not associated with decline.

Normal aging and odor intensity effects on the olfactory event-related potential

Olfactory event-related potentials (OERPs) were recorded in 14 young and 14 older adults, with odor strength of isoamyl acetate manipulated to assess olfactory stimulus intensity. Young participants produced significantly larger N1/P2, N2/P3 amplitudes and shorter N1, P2 and N2 latencies than older participants. Medium- and high-odor concentrations elicited significantly shorter P2 and N2 latencies than the lowest concentration for both age groups. Odor concentration appears to affect the speed of olfactory stimulus information processing regardless of age.

Medial temporal lobe atrophy in stroke patients: relation to pre-existing dementia

OBJECTIVE

The links between stroke and Alzheimer's disease seem to be closer than expected by chance. In a previous study it was shown that up to 16% of patients admitted for stroke had pre-existing dementia. Medial temporal lobe atrophy (MTLA) is strongly associated with Alzheimer's disease. The aim of this study was to determine the prevalence of MTLA and its relation with pre-existing dementia.

METHOD

The study was conducted on 170 consecutive stroke patients (87 women; median age 75 years; 152 infarcts), who underwent non-contrast CT with temporal lobe oriented 2 mm contiguous slices at admission. A cut off point of 11.5 mm was used to differentiate patients with and without MTLA. Pre-existing dementia was assessed using the informant questionnaire on cognitive decline in the elderly (IQCODE) with a cut off score of 104.

RESULTS

Ninety four patients (55.3%) had MTLA, of whom 23 (24.5%) had pre-existing dementia; of 76 patients without MTLA, only four (5.3%) had pre-existing dementia (p=0.0007). The logistic regression analysis with MTLA as dependent variable found the following independent variables: increasing age (p<0.05), and global cerebral atrophy scores (p<0.01). The IQCODE scores just reached significance (p=0.05).

CONCLUSION

Stroke patients with MTLA are more likely to have pre-existing dementia; this suggests that Alzheimer's disease might contribute to the dementia syndrome. A longitudinal follow up is now necessary to determine whether stroke patients with MTLA and without pre-existing dementia are at increased risk of Alzheimer's disease over subsequent years.

Neuroimaging of the aging brain

Age-related white matter injury has been recognized increasingly with the improvement of brain imaging technology. Arteriosclerosis and venous collagenosis, which occur with aging, result in a spectrum of white matter changes that range from periventricular to subcortical and deep white matter hyperintensities best seen on T2 weighted magnetic resonance imaging. These white matter changes are associated not only with aging, but with hypertension and silent infarctions. Loss of brain volume and accumulation of iron in putamen occur with normal, healthy aging. This article discusses the imaging appearance of healthy aging and pathological correlates of similar appearing alterations. The imaging findings of the most common neurodegenerative disorders, Alzheimer's and Parkinson's disease, are highlighted.

Specific hippocampal volume reductions in individuals at risk for Alzheimer's disease

Our goal was to ascertain the involvement of the temporal lobe in the preclinical (not yet diagnosable) stages of dementia of the Alzheimer's type (DAT) by using MRI-derived volumes. We assessed anatomical subdivisions of the temporal lobe on three groups of carefully screened age- and education-matched elderly individuals: 27 normal elderly (NL), 22 individuals with minimal cognitive impairment (MCI), who did not fulfill DAT criteria but were regarded at high risk for future DAT, and 27 DAT individuals. We found hippocampal volume reductions of 14% for the MCI and 22% for the DAT group compared to the NL group. Utilizing regression analyses and after accounting for gender head size-age, generalized atrophy (CSF), and other temporal lobe subvolumes, the hippocampal volume separated NL from MCI individuals, correctly classifying 74%. For NL and MCI groups combined the hippocampal volume was the only temporal lobe subvolume related to delayed recall memory performance. When contrasting MCI and DAT individuals, the fusiform gyrus volume uniquely improved the ability of the hippocampal volume to separate MCI from DAT individuals from 74 to 80%. Our cross-sectional data suggest that, within the temporal lobe, specific hippocampal volume reductions separated the group at risk for DAT from the normal group. By the time impairments are sufficient to allow a diagnosis of DAT to be made, in addition to the medial temporal lobe volume reductions, the lateral temporal lobe is also showing volume reductions, most saliently involving the fusiform gyrus.