Normalization of rCBF pattern in senile dementia of the Alzheimer's type

Altered cerebral blood flow in older adults with Alzheimer's disease: a systematic review

The prevalence of Alzheimer's disease is projected to reach 13 million in the U.S. by 2050. Although major efforts have been made to avoid this outcome, so far there are no treatments that can stop or reverse the progressive cognitive decline that defines Alzheimer's disease. The utilization of preventative treatment before significant cognitive decline has occurred may ultimately be the solution, necessitating a reliable biomarker of preclinical/prodromal disease stages to determine which older adults are most at risk. Quantitative cerebral blood flow is a promising potential early biomarker for Alzheimer's disease, but the spatiotemporal patterns of altered cerebral blood flow in Alzheimer's disease are not fully understood. The current systematic review compiles the findings of 81 original studies that compared resting gray matter cerebral blood flow in older adults with mild cognitive impairment or Alzheimer's disease and that of cognitively normal older adults and/or assessed the relationship between cerebral blood flow and objective cognitive function. Individuals with Alzheimer's disease had relatively decreased cerebral blood flow in all brain regions investigated, especially the temporoparietal and posterior cingulate, while individuals with mild cognitive impairment had consistent results of decreased cerebral blood flow in the posterior cingulate but more mixed results in other regions, especially the frontal lobe. Most papers reported a positive correlation between regional cerebral blood flow and cognitive function. This review highlights the need for more studies assessing cerebral blood flow changes both spatially and temporally over the course of Alzheimer's disease, as well as the importance of including potential confounding factors in these analyses.

Effects of interventions on cerebral perfusion in the Alzheimer's disease spectrum: A systematic review

Cerebral perfusion dysfunctions are seen in the early stages of Alzheimer's disease (AD). We systematically reviewed the literature to investigate the effect of pharmacological and non-pharmacological interventions on cerebral hemodynamics in randomized controlled trials involving AD patients or Mild Cognitive Impairment (MCI) due to AD. Studies involving other dementia types were excluded. Data was searched in April 2021 on MEDLINE, Embase, and Web of Science. Risk of bias was assessed using Cochrane Risk of Bias Tool. A meta-synthesis was performed separating results from MCI and AD studies. 31 studies were included and involved 310 MCI and 792 CE patients. The MCI studies (n = 8) included physical, cognitive, dietary, and pharmacological interventions. The AD studies (n = 23) included pharmacological, physical interventions, and phytotherapy. Cerebral perfusion was assessed with PET, ASL, Doppler, fNIRS, DSC-MRI, Xe-CT, and SPECT. Randomization and allocation concealment methods and subject characteristics such as AD-onset, education, and ethnicity were missing in several papers. Positive effects on hemodynamics were seen in 75 % of the MCI studies, and 52 % of the AD studies. Inserting cerebral perfusion outcome measures, together with established AD biomarkers, is fundamental to target all disease mechanisms and understand the role of cerebral perfusion in AD.

Parametric in vivo brain imaging during activation to examine pathological mechanisms of functional failure in Alzheimer disease

Alzheimer disease (AD) patients demonstrate reduced "resting state" regional cerebral metabolic rates for glucose (rCMRglc) and reduced regional cerebral blood flow (rCBF) in cortical association areas, early and throughout the course of disease. In this paper, we hypothesize that parametric cognitive or passive stimulation, during in vivo brain imaging, can be used to elucidate the pathological basis of these flow and metabolic abnormalities in individual AD patients. Experimental data suggest that sigmoidal relations (nonliner monotonically increasing relations reaching a horizontal asymptote) exist in the normal brain between rCBF or rCMRglc, and a function F(D,P) of task difficulty D (intensity, duration, pattern complexity) and subject performance P (reaction time, accuracy, effort, attention). Pathological mechanism I, under some conditions reversible and involving neural (including synaptic) element dropout or modification with retained capacity for full activation at high values of F(D,P), is expected early in AD and should shift the rising phase of the normal sigmoidal curve to the right. Observed rCBF responses in a face-matching task in mildly-moderately demented AD patients are consistent with mechanism I. Pathological mechanisms II and III, both irreversible and involving neural element dropout with loss of capacity for maximum activation, should alter the sigmoidal brain response at all values of F(D,P), and are expected late in disease. Our hypothesis predicts that activation paradigms with a wide range of F(D,P) values could help to distinguish among the reversible and irreversible pathological mechanisms in AD, and to evaluate drug action on these mechanisms.

Cigarette smoking and cognitive performance

While some investigations into the relationship between smoking and cognitive performance have reported that smoking facilitates performance, other research has come to the opposite conclusion. A review of the literature suggests that this variance in results may be due to differences among studies in design (comparing smokers only with deprived smokers rather than with non-smokers) and also to differences in task demands. Therefore, performance of smokers having just smoked, matched smokers deprived for a brief period, and also non-smokers was contrasted on a series of tasks which ranged from repetitive and perceptually-bound tasks to complex, dynamic tasks dependent upon long-term memory. It was found that while cigarette smoking had no negative effect upon performance for simple perceptual tasks, smoking was found to exert measurable negative effects upon performance for more complex information processing tasks.