Structural and functional bases of visuospatial associative memory in older adults

Predictive value of phospho-tau/total-tau ratio in amyloid-negative Mild Cognitive Impairment

BACKGROUND

In patients with Mild Cognitive Impairment and normal biomarkers of amyloid-β deposition, prognostication remains challenging.

METHODS

We aimed at identifying clinical features, patterns of brain atrophy, and risk of subsequent conversion to dementia in a clinical cohort of consecutive patients with Mild Cognitive Impairment and normal CSF amyloid-β_1-42 presenting to our Cognitive Neurology Clinic who were followed prospectively over an average of 25 months. We stratified them as Converters/Non-Converters to dementia based on clinical follow-up and compared baseline clinical features, CSF biomarkers, and pattern of atrophy on MRI data between groups.

RESULTS

Among 111 eligible patients (mean age 65,61 years; 56,8% were male), 41 patients developed a clinical diagnosis of dementia. Subjects with low baseline p/t-tau had twofold risk of future conversion compared to high p/t-tau ratio subjects (HR = 2.0, p = 0.026). When stratifying converters according to CSF p/t-tau ratio cut off value (0,17), those with values lower than the cut-off had significantly more MRI atrophy at baseline relative to Non-Converters in limbic structures.

CONCLUSION

In Mild Cognitive Impairment patients with negative CSF amyloid biomarker, CSF p/t-tau ratio may be useful to identify those at greater risk of subsequent conversion, possibly because of TDP43-related underlying pathology.

Impact of low-frequency rTMS on functional connectivity of the dentate nucleus subdomains in schizophrenia patients with auditory verbal hallucination

Despite low-frequency repetitive transcranial magnetic stimulation (rTMS) is effective in treating schizophrenia patients with auditory verbal hallucinations (AVH), the underlying neural mechanisms of the effect still need to be clarified. Using the cerebellar dentate nucleus (DN) subdomain (dorsal and versal DN) as seeds, the present study investigated resting state functional connectivity (FC) alternations of the seeds with the whole brain and their associations with clinical responses in schizophrenia patients with AVH receiving 1 Hz rTMS treatment. The results showed that the rTMS treatment improved the psychiatric symptoms (e.g., AVH and positive symptoms) and certain neurocognitive functions (e.g., visual learning and verbal learning) in the patients. In addition, the patients at baseline showed increased FC between the DN subdomains and temporal lobes (e.g., right superior temporal gyrus and right middle temporal gyrus) and decreased FC between the DN subdomains and the left superior frontal gyrus, right postcentral gyrus, left supramarginal gyrus and regional cerebellum (e.g., lobule 4-5) compared to controls. Furthermore, these abnormal DN subdomain connectivity patterns did not persist and decreased FC of DN subdomains with cerebellum lobule 4-5 were reversed in patients after rTMS treatment. Linear regression analysis showed that the FC difference values of DN subdomains with the temporal lobes, supramarginal gyrus and cerebellum 4-5 between the patients at baseline and posttreatment were associated with clinical improvements (e.g., AVH and verbal learning) after rTMS treatment. The results suggested that rTMS treatment may modulate the neural circuits of the DN subdomains and hint to underlying neural mechanisms for low-frequency rTMS treating schizophrenia with AVH.

Eliciting Implicit Awareness in Alzheimer’s Disease and Mild Cognitive Impairment: A Task-Based Functional MRI Study

Background

Recent models of anosognosia in dementia have suggested the existence of an implicit component of self-awareness about one’s cognitive impairment that may remain preserved and continue to regulate behavioral, affective, and cognitive responses even in people who do not show an explicit awareness of their difficulties. Behavioral studies have used different strategies to demonstrate implicit awareness in patients with anosognosia, but no neuroimaging studies have yet investigated its neural bases.

Methods

Patients with amnestic mild cognitive impairment and dementia due to Alzheimer’s disease underwent functional magnetic resonance imaging (fMRI) during the execution of a color-naming task in which they were presented with neutral, negative, and dementia-related words (Dementia-Related Emotional Stroop).

Results

Twenty-one patients were recruited: 12 were classified as aware and 9 as unaware according to anosognosia scales (based on clinical judgment and patient-caregiver discrepancy). Behavioral results showed that aware patients took the longest time to process dementia-related words, although differences between word types were not significant, limiting interpretation of behavioral results. Imaging results showed that patients with preserved explicit awareness had a small positive differential activation of the posterior cingulate cortex (PCC) for the dementia-related words condition compared to the negative words, suggesting attribution of emotional valence to both conditions. PCC differential activation was instead negative in unaware patients, i.e., lower for dementia-related words relative to negative-words. In addition, the more negative the differential activation, the lower was the Stroop effect measuring implicit awareness.

Conclusion

Posterior cingulate cortex preserved response to dementia-related stimuli may be a marker of preserved implicit self-awareness.

Late-life cognitive decline is associated with hippocampal volume, above and beyond its associations with traditional neuropathologic indices

INTRODUCTION

Reduced hippocampal volume is associated with late-life cognitive decline, but prior studies have not determined whether this association persists after accounting for Alzheimer's disease (AD) and other neuropathologies.

METHODS

Participants were 531 deceased older adults from community-based cohort studies of aging who had undergone annual cognitive evaluations. At death, brain tissue underwent neuropathologic examination and magnetic resonance imaging (MRI). Linear mixed models examined whether hippocampal volume measured via MRI accounted for variation in decline rate of global cognition and five cognitive domains, above and beyond neuropathologic indices.

RESULTS

Demographics and indices of AD, cerebrovascular disease, Lewy body disease, hippocampal sclerosis, TDP-43, and atherosclerosis accounted for 42.6% of the variation in global cognitive decline. Hippocampal volume accounted for an additional 5.4% of this variation and made similar contributions in four of the five cognitive domains.

DISCUSSION

Hippocampal volume is associated with late-life cognitive decline, above and beyond contributions from common neuropathologic indices.

The importance of the ventromedial prefrontal cortex for associative memory in older adults: A latent structural equation analysis

Older adults show relatively minor age-related decline in memory for single items, while their memory for associations is markedly reduced. Inter-individual differences in memory function in older adults are substantial but the neurobiological underpinnings of such differences are not well understood. In particular, the relative importance of inter-individual differences in the medio-temporal lobe (MTL) and the lateral prefrontal cortex (PFC) for associative and item recognition in older adults is still ambiguous. We therefore aimed to first establish the distinction between inter-individual differences in associative memory (recollection-based) performance and item memory (familiarity-based) performance in older adults and subsequently link these two constructs to differences in cortical thickness in the MTL and lateral PFC regions, in a latent structural equation modelling framework. To this end, a sample of 160 older adults (65-75 years old) performed three intentional item-associative memory tasks, of which a subsample (n ​= ​72) additionally had cortical thickness measures in MTL and PFC regions of interest available. The results provided support for a distinction between familiarity-based item memory and recollection-based associative memory performance in older adults. Cortical thickness in the ventro-medial prefrontal cortex was positively correlated with associative recognition performance, above and beyond any relationship between item recognition performance and cortical thickness in the same region and between associative recognition performance and brain structure in the MTL (parahippocampus). The findings highlight the relative importance of the ventromedial prefrontal cortex in allowing for intentional recollection-based associative memory functioning in older adults.

Sex Matters: Hippocampal Volume Predicts Individual Differences in Associative Memory in Cognitively Normal Older Women but Not Men

The hippocampus plays a prominent role in associative memory by supporting relational binding and recollection processes. Structural atrophy in the hippocampus is likely to induce associative memory deficits in older adults. Previous studies have primarily focused on average age-related differences in hippocampal structure and memory performance. To date, however, it remains unclear whether individual differences in hippocampal morphometry underlie differential associative memory performance, and whether there are sex differences in the structural correlates of associative memory in healthy older adults. Here, we used voxel-based morphometry (VBM) to examine the extent to which gray matter volume (GMV) of the hippocampus predicts associative memory performance in cognitively normal older adults. Seventy-one participants completed a cued recall paired-associative learning test (PALT), which consists of novel associations and semantically related associations, and underwent magnetic resonance imaging (MRI). We observed worse associative memory performance and larger variability for novel associations than for semantically related associations. The VBM results revealed that higher scores on associative memory for novel associations were related to greater hippocampal GMV across all older adults. When considering men and women separately, the correlation between hippocampal GMV and associative memory performance for novel associations reached significance only in older women. These findings suggest that hippocampal structural volumes may predict individual differences in novel associative memory in older women but not men.

Decreased activity with increased background network efficiency in amnestic MCI during a visuospatial working memory task

Recent studies have demonstrated the working memory impairment in patients with amnestic mild cognitive impairment (aMCI). However, the neurophysiological basis of the working memory deficit in aMCI is poorly understood. The aim of this study was to explore the abnormal activity during encoding and recognition procedures, as well as the reorganization of the background network maintaining the working memory state in aMCI. Using event-related fMRI during a visuospatial working memory task with three recognition difficulty levels, the task-related activations and network efficiency of the background network in 17 aMCI patients and 19 matched controls were investigated. Compared with cognitively healthy controls, patients with aMCI showed significantly decreased activity in the frontal and visual cortices during the encoding phase, while during the recognition phase, decreased activity was detected in the frontal, parietal, and visual regions. In addition, increased local efficiency was also observed in the background network of patients with aMCI. The results suggest patients with aMCI showed impaired encoding and recognition functions during the visuospatial working memory task, and may pay more effort to maintain the cognitive state. This study extends our understanding of the impaired working memory function in aMCI and provides a new perspective to investigate the compensatory mechanism in aMCI.

Visual memory profiling with CANTAB in mild cognitive impairment (MCI) subtypes

OBJECTIVE

Although visual memory has been shown to be impaired in amnestic mild cognitive impairment (aMCI), the differences between MCI subtypes are not well defined. The current study attempted to investigate visual memory profiles in different MCI subtypes.

METHODS

One hundred and seventy volunteers aged older than 50 years performed several visual memory tests included in the CANTAB battery. Participants were classified into four groups: (1) multiple domain aMCI (mda-MCI) (32 subjects); (2) single domain aMCI (sda-MCI)(57 subjects); (3) multiple domain non amnestic MCI (mdna-MCI) (32 subjects); and (4) controls (54 healthy individuals without cognitive impairment). Parametric and non parametric analyses were performed to compare the groups and to obtain their corresponding memory profiles.

RESULTS

The mda-MCI group exhibited impairments in both dimensions of episodic memory (recognition and recollection/recall), and also in learning and working memory, whereas the sda-MCI only showed impairment in recollection-delayed recall and learning. The mdna-MCI group displayed impairment in working memory but good preservation of learning and episodic memory.

CONCLUSION

The CANTAB visual memory profiles may contribute to better cognitive characterization of patients with different MCI subtypes, allowing comparison across several processes involved in visual memory such as attention, recognition, recollection and working memory.

Cerebral cortex involvement in Machado-Joseph disease

BACKGROUND AND PURPOSE

Machado-Joseph disease (MJD/SCA3) is the most frequent spinocerebellar ataxia, characterized by brainstem, basal ganglia and cerebellar damage. Few magnetic resonance imaging based studies have investigated damage in the cerebral cortex. The objective was to determine whether patients with MJD/SCA3 have cerebral cortex atrophy, to identify regions more susceptible to damage and to look for the clinical and neuropsychological correlates of such lesions.

METHODS

Forty-nine patients with MJD/SCA3 (mean age 47.7 ± 13.0 years, 27 men) and 49 matched healthy controls were enrolled. All subjects underwent magnetic resonance imaging scans in a 3 T device, and three-dimensional T1 images were used for volumetric analyses. Measurement of cortical thickness and volume was performed using the FreeSurfer software. Groups were compared using ancova with age, gender and estimated intracranial volume as covariates, and a general linear model was used to assess correlations between atrophy and clinical variables.

RESULTS

Mean CAG expansion, Scale for Assessment and Rating of Ataxia (SARA) score and age at onset were 72.1 ± 4.2, 14.7 ± 7.3 and 37.5 ± 12.5 years, respectively. The main findings were (i) bilateral paracentral cortex atrophy, as well as the caudal middle frontal gyrus, superior and transverse temporal gyri, and lateral occipital cortex in the left hemisphere and supramarginal gyrus in the right hemisphere; (ii) volumetric reduction of basal ganglia and hippocampi; (iii) a significant correlation between SARA and brainstem and precentral gyrus atrophy. Furthermore, some of the affected cortical regions showed significant correlations with neuropsychological data.

CONCLUSIONS

Patients with MJD/SCA3 have widespread cortical and subcortical atrophy. These structural findings correlate with clinical manifestations of the disease, which support the concept that cognitive/motor impairment and cerebral damage are related in disease.

Do the Cambridge Neuropsychological Test Automated Battery episodic memory measures discriminate amnestic mild cognitive impairment?

OBJECTIVE

Although visual recognition memory and visuospatial paired associates learning has been shown to be impaired in amnestic mild cognitive impairment (aMCI), the sensitivity and specificity of the visual memory tests used to identify aMCI are not well defined. The current study attempted to analyze the sensitivity and specificity of three visual episodic memory tests (Pattern Recognition Memory [PRM], Delayed Matching to Sample [DMS], and Paired Associated Learning [PAL]) from the CANTAB, in differentiating aMCI patients from control healthy participants.

METHODS

Seventy seven aMCI patients and 85 cognitive normal controls aged over 50 years performed the PRM, DMS, and PAL tests. Univariate and multivariate logistic regression and receiver operating characteristic curve analyses were used to study the relationships between aMCI and visual memory measures.

RESULTS

The three Cambridge Neuropsychological Test Automated Battery measures significantly predicted aMCI. The optimal predictive model combined the total percent correct responses for PRM and DMS with the PAL total errors (six shapes adjusted), with a sensitivity of 72%, specificity of 83%, and achieved predictive accuracy of 80%.

CONCLUSION

Visual episodic memory tasks such as those involved in the PRM, DMS, and PAL tests (included in the Cambridge Neuropsychological Test Automated Battery) may sensitively discriminate aMCI patients from normal controls. These tests may be useful for correct diagnosis of aMCI.

Resting functional connectivity reveals residual functional activity in Alzheimer's disease

BACKGROUND

Functional magnetic resonance imaging (fMRI) has great potential for measuring mechanisms of functional changes in Alzheimer's disease (AD) and mild cognitive impairment, but task fMRI studies have produced conflicting results, partly due to failure to account for underlying morphological changes and to variations in patients' ability to perform the tasks. Resting fMRI has potential for assessing brain function independently from a task, but greater understanding of how networks of resting functional connectivity relate to the functioning of the brain is needed. We combined resting fMRI and task fMRI to examine the correspondence between these methods in individuals with cognitive impairment.

METHODS

Eighty elderly (25 control subjects, 25 mild cognitive impairment, 30 AD) underwent a combined multimodal magnetic resonance imaging protocol including task fMRI and resting fMRI. Task fMRI data were acquired during the execution of a memory paradigm designed to account for differences in task performance. Structural and physiological confounds were modeled for both fMRI modalities.

RESULTS

Successful recognition was associated with increased task fMRI activation in lateral prefrontal regions in AD relative to control subjects; this overlapped with increased resting fMRI functional connectivity in the same regions.

CONCLUSIONS

Our results show that task fMRI and resting fMRI are sensitive markers of residual ability over the known changes in brain morphology and cognition occurring in AD and suggest that resting fMRI has a potential to measure the effect of new treatments.

Computerized adaptation of The Placing Test for early detection of both mild cognitive impairment and Alzheimer's disease

Changes in the hippocampal system have been proposed as a possible marker of incipient Alzheimer's disease (AD) at the mild cognitive impairment (MCI) stage. The Placing Test (TPT) evaluates the efficiency of the hippocampal system by measuring the ability to remember associations between images and their locations. Our aim was to validate a novel paper-and-pencil (PnP) version of TPT featuring people's faces in color (versus the traditional test carried out with black-and-white images) and a computerized Placing test with categories of objects, faces, and animals (versus a version featuring the categories of objects, faces, and shapes). A total of 78 subjects were divided into 2 groups; each group included 20 normal control subjects, 10 subjects with MCI, and 9 with AD. All subjects underwent TPT. The correlation between the two versions of the test was highly significant (r=.770, p<.001), demonstrating that the transfer of the test format from PnP to computer was acceptable. Computerized object and animal subtests had the highest overall sensitivity and specificity for discriminating MCI from AD, while PnP faces in color discriminated controls from MCI best. Although this was a preliminary assessment on a small sample of subjects, the results of our study demonstrated that total scores on both the traditional and computerized versions of the test discriminate all three diagnostic categories, but the subtests had varying discriminatory abilities.