Influence of mild cognitive impairment on visual word recognition

Predicting Scores on the Mini-Mental State Examination (MMSE) from Spontaneous Speech

The aim of this study was to examine the relationship between language components, such as lexical density, length, and content in terms of “Time, Space and Action”, with MMSE scores. For this reason, a group of 33 older participants, without a diagnosis of dementia, was examined, providing information regarding recent and future events. Participants with higher MMSE scores showed higher lexical density, speech length, as well as number of tokens related to Time, Place and Action in their speech. However, these differences only reach the statistical level for lexical density when participants were divided into two groups (MCI and healthy controls). Word frequency was lower for participants with MCI but this difference was not statistically significant. Lastly, lexical density was positively correlated with MMSE scores and predicted MMSE scores. These results could be of interest at the applied level in the screening of MCI.

Same Same But Different: Processing Words in the Aging Brain

Reading is not only one of the most appreciated leisure activities of the elderly but it clearly helps older people to maintain functional independence, which has a significant impact on life quality. Yet, very little is known about how aging affects the neural circuits of the processes that underlie skilled reading. Therefore, the aim of the present study was to systematically investigate the neural correlates of sublexical, orthographic, phonological and lexico-semantic processing in the aging brain. Using functional magnetic resonance imaging, we recorded brain activity of younger (N = 20; 22-35 years) and older (N = 38; 65-76 years) adults during letter identification, lexical decision, phonological decision and semantic categorization. Older and younger adults recruited an identical set of reading-related brain regions suggesting that the general architecture of the reading network is preserved across the lifespan. However, we also observed age-related differences in brain activity in the subcomponents of the reading network. Age-related differences were most prominent during phonological and orthographic processing possibly due to a failure of older adults to inhibit non-optimal reading strategies. Neural effects of aging were also observed outside reading-related circuits, especially in frontal midline regions. These regions might be involved because of their important role in memory, attention and executive control functions and their potential role in resting-state networks.

Drifting through Basic Subprocesses of Reading: A Hierarchical Diffusion Model Analysis of Age Effects on Visual Word Recognition

Reading is one of the most popular leisure activities and it is routinely performed by most individuals even in old age. Successful reading enables older people to master and actively participate in everyday life and maintain functional independence. Yet, reading comprises a multitude of subprocesses and it is undoubtedly one of the most complex accomplishments of the human brain. Not surprisingly, findings of age-related effects on word recognition and reading have been partly contradictory and are often confined to only one of four central reading subprocesses, i.e., sublexical, orthographic, phonological and lexico-semantic processing. The aim of the present study was therefore to systematically investigate the impact of age on each of these subprocesses. A total of 1,807 participants (young, N = 384; old, N = 1,423) performed four decision tasks specifically designed to tap one of the subprocesses. To account for the behavioral heterogeneity in older adults, this subsample was split into high and low performing readers. Data were analyzed using a hierarchical diffusion modeling approach, which provides more information than standard response time/accuracy analyses. Taking into account incorrect and correct response times, their distributions and accuracy data, hierarchical diffusion modeling allowed us to differentiate between age-related changes in decision threshold, non-decision time and the speed of information uptake. We observed longer non-decision times for older adults and a more conservative decision threshold. More importantly, high-performing older readers outperformed younger adults at the speed of information uptake in orthographic and lexico-semantic processing, whereas a general age-disadvantage was observed at the sublexical and phonological levels. Low-performing older readers were slowest in information uptake in all four subprocesses. Discussing these results in terms of computational models of word recognition, we propose age-related disadvantages for older readers to be caused by inefficiencies in temporal sampling and activation and/or inhibition processes.

Where do we stand on the relationship between tau biomarkers and mild cognitive impairment?

We present an editorial on a recent publication by Amlien et al. [2013] in which diffusion tensor imaging (DTI) was used to quantify longitudinal decreases in fractional anisotropy (FA) and increased radial diffusivity (DR) in patients with mild cognitive impairment (MCI). These longitudinal alterations were found to be greater in MCI patients with high cerebrospinal fluid (CSF) tau levels at baseline and greater than healthy controls. Amlien et al. concluded that tau levels were an important early biomarker for predicting rate of disease progression and outcome. The results of this study are an interesting finding for possible predictive use of tau levels in MCI. However, in our assessment, the methodology does not support the conclusion that CSF total tau levels are predictive of MCI progression towards a disease state such as Alzheimer's disease (AD). Further longitudinal study is needed, that includes follow-up neuropsychological assessment and conversion of subjects in the study to AD, to conclude that CSF total tau levels represent a predictive biomarker of MCI progression towards AD.

Staging neurodegenerative disorders: structural, regional, biomarker, and functional progressions

The notion of staging in the neurodegenerative disorders is modulated by the constant and progressive loss of several aspects of brain structural integrity, circuitry, and neuronal processes. These destructive processes eventually remove individuals' abilities to perform at sufficient and necessary functional capacity at several levels of disease severity. The classification of (a) patients on the basis of diagnosis, risk prognosis, and intervention outcome, forms the basis of clinical staging, and (b) laboratory animals on the basis of animal model of brain disorder, extent of insult, and dysfunctional expression, provides the components for the clinical staging and preclinical staging, respectively, expressing associated epidemiological, biological, and genetic characteristics. The major focus of clinical staging in the present account stems from the fundamental notions of Braak staging as they describe the course and eventual prognosis for Alzheimer's disease, Lewy Body dementia, and Parkinson's disease. Mild cognitive impairment, which expresses the decline in episodic and semantic memory performance below the age-adjusted normal range without marked loss of global cognition or activities of daily living, and the applications of longitudinal magnetic resonance imaging, major instruments for the monitoring of either disease progression in dementia, present important challenges for staging concepts. Although Braak notions present the essential basis for further developments, current staging conceptualizations seem inadequate to comply with the massive influx of information dealing with neurodegenerative processes in brain, advanced both under clinical realities, and discoveries in the laboratory setting. The contributions of various biomarkers of disease progression, e.g., amyloid precursor protein, and neurotransmitter system imbalances, e.g., dopamine receptor supersensitivity and interactive propensities, await their incorporation into the existing staging models thereby underlining the ongoing, dynamic feature of the staging of brain disorders.

Physical exercise alleviates debilities of normal aging and Alzheimer's disease

Both healthy aging and the pathologic incidence of disorders associated with aging involve an array of debilities. Physical exercise harnesses implicit and inherent biologic characteristics amenable to the putative interventional influences under clinical, institutional or laboratory conditions. The neurodegenerative and pathophysiologic progressions that constitute Alzheimer's disease (AD), amnestic mild cognitive impairment (aMCI), normal aging, and different animal models of AD have shown the existence of several putative mechanisms. A large variety of moderating factors have demonstrated that the ever-proliferating plethora of neurotrophic factors, neurogenesis as observed through generality of expression and neuronal arborization. The insistent efficacy of brain vascular angiogenesis may delay also the comorbid incidence of depressive disorders with dementia pathology. The pathogenesis of aging may be contained by selective treatments: these diverse conditions, linked to the basis of the aging concept, have been shown, to greater or lesser extents, to respond to a variety of scheduled applications of physical exercise. The range of reports that provide accounts of the mechanisms mediating the positive progressive response to exercise intervention is far-ranging; these studies indicate that subtle changes at molecular, neuronal, vascular and epigenetic levels may exert notable consequence at functional expression and, perhaps most essentially, offer convincing expectancy of significant benefits.

Functional response in ventral temporal cortex differentiates mild cognitive impairment from normal aging

This study sought to identify altered brain activation patterns in amnestic mild cognitive impairment (MCI) that could precede frank task impairment and neocortical atrophy. A high-accuracy lexical decision (LD) task was therefore employed. Both MCI and normal seniors (NS) groups completed the LD task while functional magnetic resonance imaging (fMRI) was performed. Accuracy on the LD task was high (> or =89% correct for both groups), and both groups activated a network of occipitotemporal regions and inferior frontal cortex. However, compared with the NS group, the MCI group showed reduced fMRI activation in these regions and increased activation in bilateral portions of anterior cingluate cortex. The results from a voxel-based morphometry analysis indicated that altered activations in the MCI group were not within regions of atrophy. Receiver operating characteristic curves demonstrated that reduced fMRI response in the left and right midfusiform gyri accurately discriminated MCI from NS. When activation magnitude in both fusiform gyri were included in a single logistic regression model, group classification accuracy was very high (area under the curve = 0.93). These results showed that a disrupted functional response in the ventral temporal lobe accurately distinguishes individuals with MCI from NS, a finding which may have implications for identifying seniors at risk for cognitive decline.