Eini Niskanen

Increased fMRI responses during encoding in mild cognitive impairment

Structural and functional magnetic resonance imaging (fMRI) was performed on 21 healthy elderly controls, 14 subjects with mild cognitive impairment (MCI) and 15 patients with mild Alzheimers disease (AD) to investigate changes in fMRI activation in relation to underlying structural atrophy. The fMRI paradigm consisted of associative encoding of novel picture-word pairs. Structural analysis of the brain was performed using voxel-based morphometry (VBM) and hippocampal volumetry. Compared to controls, the MCI subjects exhibited increased fMRI responses in the posterior hippocampal, parahippocampal and fusiform regions, while VBM revealed more atrophy in MCI in the anterior parts of the left hippocampus. Furthermore, the hippocampal volume and parahippocampal activation were negatively correlated in MCI, but not in controls or in AD. We suggest that the increased fMRI activation in MCI in the posterior medial temporal and closely connected fusiform regions is compensatory due to the incipient atrophy in the anterior medial temporal lobe.

Multi-Method Analysis of MRI Images in Early Diagnostics of Alzheimer's Disease

The role of structural brain magnetic resonance imaging (MRI) is becoming more and more emphasized in the early diagnostics of Alzheimers disease (AD). This study aimed to assess the improvement in classification accuracy that can be achieved by combining features from different structural MRI analysis techniques. Automatically estimated MR features used are hippocampal volume, tensor-based morphometry, cortical thickness and a novel technique based on manifold learning. Baseline MRIs acquired from all 834 subjects (231 healthy controls (HC), 238 stable mild cognitive impairment (S-MCI), 167 MCI to AD progressors (P-MCI), 198 AD) from the Alzheimers Disease Neuroimaging Initiative (ADNI) database were used for evaluation. We compared the classification accuracy achieved with linear discriminant analysis (LDA) and support vector machines (SVM). The best results achieved with individual features are 90% sensitivity and 84% specificity (HC/AD classification), 64%/66% (S-MCI/P-MCI) and 82%/76% (HC/P-MCI) with the LDA classifier. The combination of all features improved these results to 93% sensitivity and 85% specificity (HC/AD), 67%/69% (S-MCI/P-MCI) and 86%/82% (HC/P-MCI). Compared with previously published results in the ADNI database using individual MR-based features, the presented results show that a comprehensive analysis of MRI images combining multiple features improves classification accuracy and predictive power in detecting early AD. The most stable and reliable classification was achieved when combining all available features.

Voxel-based morphometry to detect brain atrophy in progressive mild cognitive impairment.

Recent research has shown an increased rate of conversion to dementia in subjects with mild cognitive impairment (MCI) compared to controls. However, there are no specific methods to predict who will later develop dementia. In the present study, 22 controls and 56 MCI subjects were followed on average for 37 months (max. 60 months) and studied with magnetic resonance imaging (MRI) at baseline to assess changes in brain structure associated to later progression to dementia. Voxel-based morphometry (VBM) was used to investigate gray matter atrophy. During the follow-up, 13 subjects progressed to dementia. At baseline, no differences were detected in age or education between the control and MCI subjects, but they differed by several neuropsychological tests. The stable and progressive MCI subjects differed only by CDR sum of boxes scores and delayed verbal recall, which were also significant predictors of conversion to dementia. At the baseline imaging, the MCI subjects showed reduced gray matter density in medial temporal, temporoparietal as well as in frontal cortical areas compared to controls. Interestingly, the progressive MCI subjects showed atrophy in the left temporoparietal and posterior cingulate cortices and in the precuneus bilaterally, and a trend for hippocampal atrophy when compared to the stable MCI subjects. We conclude that widespread cortical atrophy is present already two and a half years before a clinical diagnosis of dementia can be set.

The effect of midlife physical activity on structural brain changes in the elderly

Physical activity has been associated with decreased dementia risk in recent studies, but the effects for structural brain changes (i.e. white matter lesions (WML) and/or brain atrophy) have remained unclear. The CAIDE participants were a random population-based sample studied in midlife and re-examined on average 21 years later (n=2000). A subpopulation (n=75; 31 control, 23 MCI, 21 dementia) was MRI scanned at the re-examination. T1-weighted images were used to investigate grey matter (GM) density, and FLAIR-images for WML rating. Persons who actively participated in physical activity at midlife tended to have larger total brain volume (β 0.12; 95% CI 0.17-1.16, p=0.10) in late-life than sedentary persons even after adjustments. GM volume was larger among the active (β 0.19; 95% CI 0.07-1.48, p=0.03), whereas the association between midlife physical activity and larger WM volume became non-significant (β 0.03; 95% CI -0.64 to 0.86, p=0.77) after full adjustments. The differences in the GM density localized mainly in frontal lobes. There was no significant association between midlife physical activity and severe WML later in life after full adjustments (OR 4.20, 95% CI 0.26-69.13, p=0.32).

Motor potentials evoked by navigated transcranial magnetic stimulation in healthy subjects.

Summary: Navigated transcranial magnetic stimulation (TMS) is a tool for targeted, noninvasive stimulation of cerebral cortex. Transcranial stimuli can depolarize neurons and evoke measurable effects which are unique in two ways: the effects are caused directly and without a consciousness of the subject, and, the responses from peripheral muscles provide a direct measure for the integrity of the whole motor pathway. The clinical relevance of the method has not always been fully exposed because localizing the optimal stimulation site and determining the optimal stimulation strength have been dependent on time-consuming experimentation and skill. Moreover, in many disorders it has been uncertain, whether the lack of motor responses is the result of true pathophysiological changes or merely because of unoptimal stimulation. We characterized the muscle responses from human primary motor cortex system by navigated TMS to provide normative values for the clinically relevant TMS parameters on 65 healthy volunteers aged 22 to 81 years. We delivered focal TMS pulses on the primary motor area (M1) and recorded muscle responses on thenar and anterior tibial muscles. Motor threshold, latencies and amplitudes of motor-evoked potentials, and silent period duration were measured. The correction of the motor-evoked potential latency for subjects’ height is provided. In conclusion, we provide a modified baseline of TMS-related parameters for healthy subjects. Earlier such large-scale baseline material has not been available.

Atrophic Enlargement of CSF Volume after Subarachnoid Hemorrhage: Correlation with Neuropsychological Outcome

BACKGROUND AND PURPOSE: Ventricular dilation and sulcal enlargement are common sequelae after aSAH. Our aim was to quantify the late ventricular dilation and volumes of the CSF spaces after aSAH and to determine if they correlate with neurologic and cognitive impairments frequently detected in these patients. MATERIALS AND METHODS: 3D T1-weighted images needed for volumetry were available in 76 patients 1 year after aSAH, along with 75 neuropsychological assessments. Volumes of CSF segments and ICV were quantified by SPM in 76 patients and 30 control subjects to determine CSF/ICV ratios. The mCMI was calculated to roughly evaluate the ventricular dilation. The contributing factors for enlarged ventricles and CSF volumes were reviewed from radiologic, clinical, and neuropsychological perspectives. RESULTS: The mCMI was higher in patients with aSAH (0.23 ± 0.06) compared with control subjects (0.20 ± 0.04; P = .020). In line with these planimetric measurements, the SPM-based CSF/ICV ratios were higher in patients with aSAH (35.58 ± 7.0) than in control subjects (30.36 ± 6.25; P = .001). Preoperative hydrocephalus, higher HH and Fisher grades, and focal parenchymal lesions on brain MR imaging, but not the treatment technique, were associated with ventricular enlargement. The clinical outcome and presence of neuropsychological deficits correlated significantly with CSF enlargement. CONCLUSIONS: Ventricular and sulcal enlargement, together with reduced GM volumes, after aSAH may indicate general atrophy rather than hydrocephalus. Enlarged CSF spaces correlate with cognitive deficits after aSAH. A simple measure, mCMI proved to be a feasible tool to assess the diffuse atrophic brain damage after aSAH.

Brain atrophy and neuropsychological outcome after treatment of ruptured anterior cerebral artery aneurysms: a voxel-based morphometric study

IntroductionCognitive impairment after aneurysmal subarachnoid hemorrhage (aSAH) is frequently detected. Here, we describe the pattern of cerebral (gray matter) atrophy and its clinical relevance after treatment of aSAH caused by a ruptured anterior cerebral artery (ACA) aneurysm.MethodsThirty-seven aSAH patients with ACA aneurysm (17 surgical, 20 endovascular treatment) and a good or moderate clinical outcome (Glasgow Outcome Scale V or IV) and 30 controls underwent brain MRI. Voxel-based morphometric analysis was applied to compare the patients and controls. Patients also underwent a detailed neuropsychological assessment.ResultsThe comparisons between controls and either all patients (n = 37) or the subgroup of surgically treated patients (n = 17) revealed bilateral cortical atrophy in the frontal lobes, mainly in the basal areas. The brainstem, bilateral thalamic and hypothalamic areas, and ipsilateral caudate nucleus were also involved. Small areas of atrophy were detected in temporal lobes. The hippocampus and parahippocampal gyrus showed atrophy ipsilateral to the surgical approach. In the subgroup of endovascularly treated patients (n = 15), small areas of atrophy were detected in the bilateral orbitofrontal cortex and in the thalamic region. Twenty patients (54%) showed cognitive deficits in neuropsychological assessment.ConclusionGroup analysis after aSAH and treatment of the ruptured ACA aneurysm revealed gray matter atrophy, principally involving the frontobasal cortical areas and hippocampus ipsilateral to the surgical approach. Areas of reduced gray matter were more pronounced after surgical than endovascular treatment. Together with possible focal cortical infarctions and brain retraction deficits in individual patients, this finding may explain the neuropsychological disturbances commonly detected after treatment of ruptured ACA aneurysms.

Cortical Thickness Analysis to Detect Progressive Mild Cognitive Impairment: A Reference to Alzheimer’s Disease

Background/Aims: Mild cognitive impairment (MCI) is associated with an increased risk of Alzheimer’s disease (AD). It would be advantageous to be able to distinguish the characteristics of those MCI patients with a high probability to progress to AD if one wishes to monitor the disease development and treatment. Methods: We assessed the baseline MRI and maximum of 7 years clinical follow-up data of 60 MCI subjects in order to examine differences in cortical thickness (CTH) between the progressive MCI (P-MCI) and stable MCI (S-MCI) subjects. CTH was measured using an automatic computational surface-based method. During the follow-up, 15 MCI subjects converted to AD on average 1.9 ± 1.3 years after the baseline examination, while 45 MCI subjects remained stable. Results: The P-MCI group displayed significantly reduced CTH bilaterally in the superior and middle frontal, superior, middle and inferior temporal, fusiform and parahippocampal regions as well as the cingulate and retrosplenial cortices and also in the right precuneal and paracentral regions compared to S-MCI subjects. Conclusions: Analysis of CTH could be used in conjunction with neuropsychological testing to identify those subjects with imminent conversion from MCI to AD several years before dementia diagnosis.

Differences in cortical thickness in healthy controls, subjects with mild cognitive impairment, and Alzheimer's disease patients: a longitudinal study.

In this study, we analyzed differences in cortical thickness (CTH) between healthy controls (HC), subjects with stable mild cognitive impairment (S-MCI), progressive MCI (P-MCI), and Alzheimers disease (AD), and assessed correlations between CHT and clinical disease severity, education, and apolipoprotein E4 (APOE) genotype. Automated CTH analysis was applied to baseline high-resolution structural MR images of 145 subjects with a maximum followup time of 7.4 years pooled from population-based study databases held in the University of Kuopio. Statistical differences in CTH between study groups and significant correlations between CTH and clinical and demographic factors were assessed and displayed on a cortical surface model. Compared to HC group (n = 26), the AD (n = 21) group displayed significantly reduced CTH in several areas of frontal and temporal cortices of the right hemisphere. Higher education and lower MMSE scores were correlated with reduced CTH in the AD group, whereas no significant correlation was found between CDR-SB scores or APOE genotype and CTH. The P-MCI group demonstrated significantly reduced CTH compared to S-MCI in frontal, temporal and parietal cortices even after statistically adjusting for all confounding variables. Ultimately, analysis of CTH can be used to detect cortical thinning in subjects with progressive MCI several years before conversion and clinical diagnosis of AD dementia, irrespective of their cognitive performance, education level, or APOE genotype.

Evolution of Global and Local Grey Matter Atrophy on Serial MRI Scans During the Progression from MCI to AD

Mild cognitive impairment (MCI) often represents a prodromal form of dementia, conferring a significantly higher risk of converting to probable Alzheimers disease (AD). The aim of this study is to characterise the differences of grey matter (GM) distribution and dynamics between progressive and stable MCI subjects during a 2 year period preceding the conversion to AD. We included 48 stable MCI and 12 progressive MCI cases based on the availability of 3 serial scans acquired with approximately 1 year scan interval. For the progressive MCI group, the third scan was acquired at the time of the clinical diagnosis of AD, while the first two scans were acquired approximately 2 and 1 years earlier. For the stable MCI group, the three scans were acquired at approximately 1 year intervals during a period free from significant cognitive decline. We used longitudinal voxel-based morphometry (VBM) for mapping the progression of GM loss over time. For the progressive MCI group, the cross-sectional analysis revealed areas of lower GM volumes in the parahippocampal gyrus, precuneus and posterior cingulate 12 months before the AD diagnosis. For the longitudinal VBM analysis the progressive MCI group revealed increased GM loss in cortical regions belonging to the temporal neocortex, parahippocampal cortex, and cingulate gyrus. The frontal lobe, insula and the cerebellum were also affected. This accelerated atrophy may offer new insights into the understanding of neurodegenerative pathology and the clinical relevance of these changes remains to be verified by subsequent studies.