The National Institute on Aging and the Alzheimer's Association charged a workgroup with the task of revising the 1984 criteria for Alzheimer's disease (AD) dementia. The workgroup sought to ensure that the revised criteria would be flexible enough to be used by both general healthcare providers without access to neuropsychological testing, advanced imaging, and cerebrospinal fluid measures, and specialized investigators involved in research or in clinical trial studies who would have these tools available. We present criteria for all-cause dementia and for AD dementia. We retained the general framework of probable AD dementia from the 1984 criteria. On the basis of the past 27 years of experience, we made several changes in the clinical criteria for the diagnosis. We also retained the term possible AD dementia, but redefined it in a manner more focused than before. Biomarker evidence was also integrated into the diagnostic formulations for probable and possible AD dementia for use in research settings. The core clinical criteria for AD dementia will continue to be the cornerstone of the diagnosis in clinical practice, but biomarker evidence is expected to enhance the pathophysiological specificity of the diagnosis of AD dementia. Much work lies ahead for validating the biomarker diagnosis of AD dementia.

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The diagnosis of dementia due to Alzheimer’s disease: Recommendations from the National Institute on Aging-Alzheimer’s Association workgroups on diagnostic guidelines for Alzheimer's disease

We review evidence for partially segregated networks of brain areas that carry out different attentional functions. One system, which includes parts of the intraparietal cortex and superior frontal cortex, is involved in preparing and applying goal-directed (top-down) selection for stimuli and responses. This system is also modulated by the detection of stimuli. The other system, which includes the temporoparietal cortex and inferior frontal cortex, and is largely lateralized to the right hemisphere, is not involved in top-down selection. Instead, this system is specialized for the detection of behaviourally relevant stimuli, particularly when they are salient or unexpected. This ventral frontoparietal network works as a 'circuit breaker' for the dorsal system, directing attention to salient events. Both attentional systems interact during normal vision, and both are disrupted in unilateral spatial neglect.

Control of goal-directed and stimulus-driven attention in the brain

Co-Planar Stereotaxic Atlas of the Human Brain—3-Dimensional Proportional System: An Approach to Cerebral Imaging, J. Talairach, P. Tournoux. Georg Thieme Verlag, New York (1988), 122 pp., 130 figs. DM 268

Thirty years of brain imaging research has converged to define the brain’s default network—a novel and only recently appreciated brain system that participates in internal modes of cognition Here we synthesize past observations to provide strong evidence that the default network is a specific, anatomically defined brain system preferentially active when individuals are not focused on the external environment Analysis of connectional anatomy in the monkey supports the presence of an interconnected brain system Providing insight into function, the default network is active when individuals are engaged in internally focused tasks including autobiographical memory retrieval, envisioning the future, and conceiving the perspectives of others Probing the functional anatomy of the network in detail reveals that it is best understood as multiple interacting subsystems The medial temporal lobe subsystem provides information from prior experiences in the form of memories and associations that are the building blocks of mental simulation The medial prefrontal subsystem facilitates the flexible use of this information during the construction of self-relevant mental simulations These two subsystems converge on important nodes of integration including the posterior cingulate cortex The implications of these functional and anatomical observations are discussed in relation to possible adaptive roles of the default network for using past experiences to plan for the future, navigate social interactions, and maximize the utility of moments when we are not otherwise engaged by the external world We conclude by discussing the relevance of the default network for understanding mental disorders including autism, schizophrenia, and Alzheimer’s disease

/pdf/the-brain-s-default-network-anatomy-function-and-relevance-3sxu9umxjl.pdf

The Brain's Default Network Anatomy, Function, and Relevance to Disease

: The concept of attention as central to human performance extends back to the start of experimental psychology, yet even a few years ago, it would not have been possible to outline in even a preliminary form a functional anatomy of the human attentional system. New developments in neuroscience have opened the study of higher cognition to physiological analysis, and have revealed a system of anatomical areas that appear to be basic to the selection of information for focal (conscious) processing. The importance of attention is its unique role in connecting the mental level of description of processes used in cognitive science with the anatomical level common in neuroscience. Sperry describes the central role that mental concepts play in understanding brain function. As is the case for sensory and motor systems of the brain, our knowledge of the anatomy of attention is incomplete. Nevertheless, we can now begin to identify some principles of organization that allow attention to function as a unified system for the control of mental processing. Although many of our points are still speculative and controversial, we believe they constitute a basis for more detailed studies of attention from a cognitive-neuroscience viewpoint. Perhaps even more important for furthering future studies, multiple methods of mental chronometry, brain lesions, electrophysiology, and several types of neuro-imaging have converged on common findings.

/pdf/the-attention-system-of-the-human-brain-w797wllpat.pdf

The Attention System of the Human Brain

Positron emission tomography (PET) is a nuclear medicine technique that allows the in vivo regional quantitation o f human biochemical and physiological processes. PET was originally developed and used f or research purposes and only recently has it beenused for clinical application. Indeed, due to the interest o f industry in this technology, largely automated instrumentation has recently become commercially available at an acceptable cost. At the same time, following validation o f a large number o f subjects presenting with various pathologies, precisediagnostic protocols have been optimized. The power o f PET is in its unique ability to visualize biochemical processes. Its potential is highly enhanced when used in conjunction with other imaging techniques such as CT or MRI, in order to correlate morphology and funcion. The correlation with other techniques in the domain o felectrophysiology, such as EEG and ECG, is also essential to understand the ralationship between these conventionalphysiological signals and the biochemical measurements obtained with PET. The main features and applications o f PET are reviewed in this paper, with particular emphasis on the diagnosis of coronary artery disease, cerebrovascular and cerbral degenerative disease, epilepsy, an d tumors. Our experience on the organization o f a clinical PET/Cyclotron center is also described. Given the incidence o fthe diseaseas that can be conveniently examined by PET, a population of approximately two million is the adequate basis for a PET center. The gain in terms o f knowledge o f precise biochemical process over a vast population can be seen as a long term investment for public health.

http://link.springer.com/content/pdf/10.1007/978-94-011-2584-0_10.pdf

Clinicalaspects of positron emission tomography

Genetic endophenotypes mark the onset, clinical characteristics and disease severity in neurodegenerative diseases. The C9orf72 hexanucleotide repeat expansion (C9orf72RE) is the most common genetic cause of behavioural variant of frontal–temporal dementia (bvFTD). Dysfunctions in executive processes and social cognition represent the core symptoms of bvFTD, essential for clinical diagnosis. The presence of an extensive symptomatic overlap with psychiatric disorders, particularly for impaired social cognition is responsible for frequent misdiagnosis in the early phase of disease. Of relevance, bvFTD and psychiatric brain disorders share involvement of frontal–subcortical neuronal circuits, as confirmed by functional imaging studies.1 It is conceivable that C9orf72RE, and …

https://jnnp.bmj.com/content/jnnp/early/2021/11/23/jnnp-2021-328335.full.pdf

Daniela Perani

Papers

Clinicalaspects of positron emission tomography

Neurogenetic markers may influence behavioural phenotypes, far away from the disease onset.

Effective connectivity within the neural system for object-directed action representation during aware and unaware tool processing

Sporadic Fatal Insomnia presenting with agrypnia excitata and rapidly progressive dementia: a case report