Comparing extent of activation: a robust permutation approach

Cerebrovascular function in hypertension: Does high blood pressure make you old?

The majority of individuals over an age of 60 have hypertension. Elevated blood pressure and older age are associated with very similar changes in brain structure and function. We review the parallel brain changes associated with increasing age and blood pressure. This review focuses on joint associations of aging and elevated blood pressure with neuropsychological function, regional cerebral blood flow responses to cognitive and metabolic challenges, white matter disruptions, grey matter volume, cortical thinning, and neurovascular coupling. Treatment of hypertension ameliorates many of these changes but fails to reverse them. Treatment of hypertension itself appears more successful with better initial brain function. We show evidence that sympathetic and renal influences known to increase blood pressure also impact brain integrity. Possible central mechanisms contributing to the course of hypertension and aging are then suggested. An emphasis is placed on psychologically relevant factors: stress, cardiovascular reactions to stress, and diet/obesity. The contribution of some of these factors to biological aging remains unclear and may provide a starting point for defining the independent and interacting effects of aging and increasing blood pressure on the brain.

Executive function in systemic arterial hypertension: A systematic review

Systemic arterial hypertension (SAH) may be associated with worse cognitive performance, especially in tasks that evaluate the executive functions (EF).

OBJECTIVE

we aimed to review the evidence regarding which components of executive functions are most affected in adults with SAH.

METHODS

this systematic review used the PRISMA statement for searching Pubmed, Scielo and Lilacs databases with the keywords "executive function OR executive functioning AND hypertension".

RESULTS

EF tasks were divided into shifting, inhibitory control and updating. A total of 9 cross-sectional and 3 longitudinal studies were selected. Only 3 studies did not report worse performance among SAH patients on EF tasks when compared to normotensive controls. The measures of shifting and inhibitory control were the most frequently investigated and reported as altered among SAH individuals, assessed mainly by the Stroop Test and Trail-Making Test part B, respectively.

CONCLUSION

inhibitory control and shifting are the EF components most influenced by SAH. The results of this review may contribute to the devising of hypotheses about mechanisms underlying these cognitive impairments.

Disrupted Frontoparietal Network Mediates White Matter Structure Dysfunction Associated with Cognitive Decline in Hypertension Patients

Some previous reports have suggested that hypertension is a risk factor for dementia and cognitive impairments. Using behavioral data from 1007 elderly human subjects (405 hypertensive patients) of Han ethnicity from Beijing, China, the present study aimed to assess the effects of hypertension on cognitive performance and explore related neuronal changes via advanced resting-state functional magnetic resonance imaging and diffusion tensor imaging data from 84 of these subjects (44 hypertensive patients). Cognitively, we found that patients with hypertension showed decreased executive functions and attention compared with those with normotension in the large sample. In magnetic resonance imaging scan sample, using independent component analysis to examine the functional connectivity difference between the two groups, we found that the frontoparietal networks in the hypertensive group exhibited altered patterns compared with the control group, mainly in the inferior parietal lobe, left inferior frontal lobe, and precuneus. Using tract-based spatial statistics to investigate the between-group structural difference, we found that the hypertensive group showed significantly reduced integrity of white matter in the bilateral superior longitudinal fasciculus. Importantly, using the mediation analysis, we found that the functional connectivity of the frontoparietal networks mediates the impact of white matter on executive function in the hypertensive group. The results demonstrate that hypertension targets a specific pattern of cognitive decline, possibly due to deficits in the white matter and functional connectivity in frontal and parietal lobes. Our findings highlight the importance of brain protection in hypertension.

SIGNIFICANCE STATEMENT

Hypertension is a risk factor for cognitive decline and dementia. However, the neural mechanism underlying cognitive decline in hypertension is largely unknown. We studied the relationship among cognitive decline, brain functional, and structural changes in hypertensive patients via advanced resting-state functional magnetic resonance imaging and diffusion tensor imaging data in a Chinese cohort. Hypertensive patients showed executive dysfunction, along with disrupted functional connectivity in frontoparietal (FP) networks and reduced integrity of white matter in the bilateral superior longitudinal fasciculus. Importantly, the functional connectivity changes mediate the impact of white matter alterations on cognitive decline in the hypertensive group. Our findings provide a better understanding of the mechanism of cognitive decline in hypertension and highlight the importance of brain protection in hypertension.

From Brain to Behavior: Hypertension's Modulation of Cognition and Affect

Accumulating evidence from animal models and human studies of essential hypertension suggest that brain regulation of the vasculature is impacted by the disease. Human neuroimaging findings suggest that the brain may be an early target of the disease. This observation reinforces earlier research suggesting that psychological factors may be one of the many contributory factors to the initiation of the disease. Alternatively or in addition, initial blood pressure increases may impact cognitive and/or affective function. Evidence for an impact of blood pressure on the perception and experience of affect is reviewed vis-a-vis brain imaging findings suggesting that such involvement in hypertensive individuals is likely.

Brain function, cognition, and the blood pressure response to pharmacological treatment

OBJECTIVE

To extend evidence suggesting that essential hypertension influences neuropsychological performance and that brain function before treatment is related to the success of pharmacological lowering of blood pressure (BP).

METHODS

A voxel-based examination of the whole brain was conducted among 43 hypertensive patients treated for 1 year with assessment pre and post treatment, using positron emission tomography and neuropsychological testing.

RESULTS

Neuropsychological performance improved over the year of treatment but was unrelated to change in regional cerebral blood flow (rCBF). Neither mean resting rCBF nor responsivity to a working memory task changed significantly with treatment. However, patients with greater lowering of systolic BP during treatment showed increased rCBF responsivity to a working memory task in medial and orbital frontal areas and decreased rCBF responsivity in mid frontal, parietal, thalamus, and pons (as well as lower thalamic rCBF pretreatment). Improved working memory performance over the treatment period was related to decreased responsivity in medial frontal, medullary, and parietal areas. Patients showing greater lowering of BP with treatment seemed to reduce excitatory and enhance inhibitory coupling between memory processing and BP more than those with less treatment success.

CONCLUSION

Degree of treatment success for both BP and cognitive performance among hypertensives is related to differing patterns of rCBF. Overall, the results emphasize the relevance of brain function to the treatment of hypertension.

Is the brain the essential in hypertension?

The brain is typically considered a target for late stage hypertensive disease due to the high prevalence of stroke among hypertensive patients. Research is reviewed, however, that suggests that the brain is implicated in the initiation of high blood pressure and is itself altered by early disease processes. A substantial literature establishes neural control of the vasculature and kidney as candidate etiological factors in essential hypertension. This research, largely done in animals, is now supplemented by behavioral and brain imaging studies in humans. This review suggests that the brain and vasculature may be independently and concurrently targeted by the factors inducing essential hypertension. Early stage hypertension is associated with cognitive deficits, altered cerebral blood flow support for cognitive processing, and decreased grey matter in specific cortical regions. Pharmacological reversal of hypertension is less successful in patients with premature brain aging and fails to reverse either the progression of functional or structural changes within the cerebral cortex. Furthermore, magnetic resonance imaging Blood Oxygen Level-Dependent (BOLD) responses during psychological challenge differ between normotensive individuals at risk and those not at risk for hypertension because of their exaggerated blood pressure responses to psychological challenge. Further examination of mechanisms of action and early influences of the disease on the brain are required to understand the pathophysiological mechanisms having concurrent influences on the brain and the peripheral vasculature.

Transient hypertension concurrent with forepaw stimulation enhances functional MRI responsiveness in infarct and peri-infarct regions

Although functional magnetic resonance imaging (fMRI) is gaining use as a tool to assess cerebral recovery following various insults, the effects of potential confounders such as hypertension are poorly defined. We hypothesized that after stroke, transient hypertension during an fMRI study could produce a detected activation unrelated to neuronal activity within the infarct. Thus, the effect of norepinephrine induced increases in blood pressure (BP) on the fMRI response to forepaw stimulation were investigated in controls or 1 week after transient middle cerebral artery occlusion in rats. Images were smoothed spatially and voxels correlating to either forepaw stimulation or the change in BP time courses were analyzed. Transient hypertension increased the signal intensity and numbers of voxels correlating to the BP time courses within and adjacent to the ischemic infarct and these exceeded the response in the contralateral hemisphere or in controls. With left paw stimulation at normotension, there was a loss of activation in right sensory-motor cortex -- a region with necrosis and disruption of cerebral vessels. As BP increased left paw stimulation also resulted in the detection of activation in the infarcted sensory-motor cortex and peri-infarct regions. Thus, BP changes synchronous with tasks in fMRI studies can result in MR signal changes consistent with a loss of cerebral blood flow (CBF) autoregulation rather than neuronal activation in necrotic brain. After stroke, the use of stressful tasks associated with BP changes in fMRI studies should be limited or the BP change should be considered as a potential source of MR signal changes.

Classification of functional brain images with a spatio-temporal dissimilarity map

Classification of subjects into predefined groups, such as patient vs. control, based on their functional MRI data is a potentially useful procedure for clinical diagnostic purposes. This paper presents an automated method for classifying subjects into groups based on their functional MRI data. The proposed methodology provides general framework using preprocessed time series for the whole brain volume. Using a training set of two groups of subjects, the new methodology identifies spatio-temporal features that distinguish the groups and uses these features to categorize new subjects. We demonstrate the method using simulations and a clinical application that classifies individuals into schizotypy and control groups.

Verbal and spatial working memory in older individuals: A positron emission tomography study

Recent reviews of a substantial number of studies have partially resolved questions concerning the brain regions used by working memory for manipulation and representation. We report a large single experiment in middle-aged to older adults (n = 89), classified by hypertensive status. Our design addresses the question of regions related to manipulation and representation, most particularly comparing spatial and verbal working memory. A control, memory search, and 2-back running memory task were performed with identical stimuli and responses during whole-brain 15O water positron emission tomography (PET) scans. Letter or spatial position instructions created verbal or spatial working memory versions of the tasks. We assessed agreement with the literature using regions of interest that were defined by clusters of activation empirically derived from the literature by Wager and Smith (Wager, T.D. and Smith, E.E., Neuroimaging studies of working memory: a meta-analysis, Cognitive, Affective and Behavioral Neuroscience, 3 (2003) 255-274). Our results largely confirmed conclusions from the review on the organization of working memory into dorsal prefrontal manipulation and ventrolateral prefrontal maintenance areas and representation in dorsal and ventral paths. Specific verbal versus spatial comparisons were also concordant with prior work establishing posterior lateralized representation for different contents by working memory. The similarity of results between this older sample and results derived by others from younger participants is notable.