Verbal Working Memory and Atherosclerosis in Patients with Cardiovascular Disease: An fMRI study

BACKGROUND AND PURPOSE: Intimal-medial thickening (IMT) of the carotid wall is an accepted peripheral marker of atherosclerosis. It is associated with increased risk for myocardial infarction and stroke, and lower attention-executive-psychomotor functioning. The purpose of this study was to examine the relationship between IMT and brain activity during a verbal working memory (VWM) task in patients with cardiovascular disease (CVD). METHODS: Thirteen CVD patients underwent functional magnetic resonance imaging (fMRI) during a 2-Back VWM task, and B-mode ultrasound of the carotid arteries. IMT was calculated using an automated algorithm based on a validated edge-detection technique. The relationship between IMT and 2-Back-related brain activity was modeled using partial correlations controlling for age and small vessel disease as measured by white matter signal hyperintensities on MRI (WMH). RESULTS: Higher IMT was associated with lower 2-Back-related signal intensity and in the right middle frontal gyrus, independent of age and WMH. CONCLUSIONS: IMT may be one mechanism contributing to brain dysfunction in CVD. The blood oxygenation level-dependent (BOLD) contrast appears to be highly sensitive to peripheral vascular health as measured by IMT. Future studies should examine the sensitivity and specificity of the BOLD response for predicting cognitive decline in CVD.     

FUNCTIONAL MAPPING OF THE HUMAN BRAIN DURING ACUPUNCTURE WITH MAGNETIC RESONANCE IMAGING SOMATOSENSORY CORTEX ACTIVATION

1NTRODUCTIONHegu(Ll4)isoneofthemosteffectiveandmostfrequentlyusedacupointsintraditionalChineseacupuncture.ItisindicatedfOrpaininmanypartsofthebody,butisparticularlyeffec-tiveforheadache,migraine,toothache,sorethroatandotherd1sordersoftheheadandface.Manyanimalexperimentsindicatethathighercentersinthenervoussystemareinvolvedinacupunctureanalgesia["2]butdirectevidenceforhumansubjectsisdifficulttoobtainuntilthere-centadventofpowerfu1andn0n-invasivemeth-odsforneuroimaginginthe9O's.Werecentlya…     

Parafoveal vision reveals qualitative differences between fusiform face area and parahippocampal place area

The center-periphery visual field axis guides early visual system organization with enhanced resources devoted to central vision leading to reduced peripheral performance relative to that of central vision (i.e., behavioral eccentricity effect) for many visual functions. The center-periphery organization extends to high-order visual cortex where, for example, the well-studied face-sensitive fusiform face area (FFA) shows sensitivity to central vision and the place-sensitive parahippocampal place area (PPA) shows sensitivity to peripheral vision. As we have recently found that face perception is more sensitive to eccentricity than place perception, here we examined whether these behavioral findings reflect differences in FFA's and PPA's sensitivities to eccentricity. We assumed FFA would show higher sensitivity to eccentricity than PPA would, but that both regions' modulation by eccentricity would be invariant to the viewed category. We parametrically investigated (fMRI, n = 32) how FFA's and PPA's activations are modulated by eccentricity (≤8°) and category (upright/inverted faces/houses) while keeping stimulus size constant. As expected, FFA showed an overall higher sensitivity to eccentricity than PPA. However, both regions' activation modulations by eccentricity were dependent on the viewed category. In FFA, a reduction of activation with growing eccentricity (“BOLD eccentricity effect”) was found (with different amplitudes) for all categories. In PPA however, qualitatively different BOLD eccentricity effect modulations were found (e.g., at 8° mild BOLD eccentricity effect for houses but a reverse BOLD eccentricity effect for faces and no modulation for inverted faces). Our results emphasize that peripheral vision investigations are critical to further our understanding of visual processing.     

Functional-anatomical validation and individual variation of diffusion tractography-based segmentation of the human thalamus

Parcellation of the human thalamus based on cortical connectivity information inferred from non-invasive diffusion-weighted images identifies sub-regions that we have proposed correspond to nuclei. Here we test the functional and anatomical validity of this proposal by comparing data from diffusion tractography, cytoarchitecture and functional imaging. We acquired diffusion imaging data in eleven healthy subjects and performed probabilistic tractography from voxels within the thalamus. Cortical connectivity information was used to divide the thalamus into sub-regions with highest probability of connectivity to distinct cortical areas. The relative volumes of these connectivity-defined sub-regions correlate well with volumetric predictions based on a histological atlas. Previously reported centres of functional activation within the thalamus during motor or executive tasks co-localize within atlas regions showing high probabilities of connection to motor or prefrontal cortices, respectively. This work provides a powerful validation of quantitative grey matter segmentation using diffusion tractography in humans. Co-registering thalamic sub-regions from 11 healthy individuals characterizes inter-individual variation in segmentation and results in a population-based atlas of the human thalamus that can be used to assign likely anatomical labels to thalamic locations in standard brain space. This provides a tool for specific localization of functional activations or lesions to putative thalamic nuclei.     

Bayesian inference of hemodynamic changes in functional arterial spin labeling data.

The study of brain function using MRI relies on acquisition techniques that are sensitive to different aspects of the hemodynamic response contiguous to areas of neuronal activity. For this purpose different contrasts such as arterial spin labeling (ASL) and blood oxygenation level dependent (BOLD) functional MRI techniques have been developed to investigate cerebral blood flow (CBF) and blood oxygenation, respectively. Analysis of such data typically proceeds by separate, linear modeling of the appropriate CBF or BOLD time courses. In this work an approach is developed that provides simultaneous inference on hemodynamic changes via a nonlinear physiological model of ASL data acquired at multiple echo times. Importantly, this includes a significant contribution by changes in the static magnetization, M, to the ASL signal. Inference is carried out in a Bayesian framework. This is able to extract, from dual-echo ASL data, probabilistic estimates of percentage changes of CBF, R(2) (*), and the static magnetization, M. This approach provides increased sensitivity in inferring CBF changes and reduced contamination in inferring BOLD changes when compared with general linear model approaches on single-echo ASL data. We also consider how the static magnetization, M, might be related to changes in CBV by assuming the same mechanism for water exchange as in vascular space occupancy.     

The effect of model order selection in group PICA

Independent component analysis (ICA) of functional MRI data is sensitive to model order selection. There is a lack of knowledge about the effect of increasing model order on independent components' (ICs) characteristics of resting state networks (RSNs). Probabilistic group ICA (group PICA) of 55 healthy control subjects resting state data was repeated 100 times using ICASSO repeatability software and after clustering of components, centrotype components were used for further analysis. Visual signal sources (VSS), default mode network (DMN), primary somatosensory (S₁), secondary somatosensory (S₂), primary motor cortex (M₁), striatum, and precuneus (preC) components were chosen as components of interest to be evaluated by varying group probabilistic independent component analysis (PICA) model order between 10 and 200. At model order 10, DMN and VSS components fuse several functionally separate sources that at higher model orders branch into multiple components. Both volume and mean z‐score of components of interest showed significant (P < 0.05) changes as a function of model order. In conclusion, model order has a significant effect on ICs characteristics. Our findings suggest that using model orders ≤20 provides a general picture of large scale brain networks. However, detection of some components (i.e., S₁, S₂, and striatum) requires higher model order estimation. Model orders 30–40 showed spatial overlapping of some IC sources. Model orders 70 ± 10 offer a more detailed evaluation of RSNs in a group PICA setting. Model orders > 100 showed a decrease in ICA repeatability, but added no significance to either volume or mean z‐score results. Hum Brain Mapp, 2010. © 2010 Wiley‐Liss, Inc.     

Women and men exhibit different cortical activation patterns during mental rotation tasks

The strongest sex differences on any cognitive task, favoring men, are found for tasks that require the mental rotation of three-dimensional objects. A number of studies have explored functional brain activation during mental rotation tasks, and sex differences have been noted in some. However, in these studies there was a substantial confounding factor because male and female subjects differed in overall performance levels. In contrast, our functional brain activation study examined cortical activation patterns for males and females who did not differ in overall level of performance on three mental rotation tasks. This allowed us to eliminate any confounding influences of overall performance levels. Women exhibited significant bilateral activations in the intraparietal sulcus (IPS) and the superior and inferior parietal lobule, as well as in the inferior temporal gyrus (ITG) and the premotor areas. Men showed significant activation in the right parieto-occitpital sulcus (POS), the left intraparietal sulcus and the left superior parietal lobule (SPL). Both men and women showed activation of the premotor areas but men also showed an additional significant activation of the left motor cortex. No significant activation was found in the inferior temporal gyrus. Our results suggest that there are genuine between-sex differences in cerebral activation patterns during mental rotation activities even when performances are similar. Such differences suggest that the sexes use different strategies in solving mental rotation tasks.     

Three‐dimensional MR‐encephalography: Fast volumetric brain imaging using rosette trajectories

MR‐Encephalography (MREG) is a technique that allows real time observation of functional changes in the brain that appears within 100 msec. The high sampling rate is achieved at the cost of some spatial resolution. The article describes a novel imaging method for fast three‐dimensional‐MR‐encephalography whole brain coverage based on rosette trajectories and the use of multiple small receiver coils. The technique allows the observation of changes in brain physiology at very high temporal resolution. A highly undersampled three‐dimensional rosette trajectory is chosen, to perform single shot acquisition of k‐space data within 23 msec. By using a 32‐channel head coil array and regularized nonuniform Fourier transformation reconstruction, the spatial resolution is sufficient to detect even subtle centers of activation (e.g. human MT+). The method was applied to visual block design paradigms and compared with echo planar imaging‐based functional MRI. As a proof‐of‐principle of the method's ability to detect local differences in the hemodynamic response functions, the analyzed MR‐encephalography data revealed a spatially dependent delay of the arrival of the blood oxygenation level dependent response within the visual cortex. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.     

Defining the brain systems of lust,romantic attraction,and attachment

Mammals and birds have evolved three primary, discrete, interrelated emotion–motivation systems in the brain for mating, reproduction, and parenting: lust, attraction, and male–female attachment. Each emotion–motivation system is associated with a specific constellation of neural correlates and a distinct behavioral repertoire. Lust evolved to initiate the mating process with any appropriate partner; attraction evolved to enable individuals to choose among and prefer specific mating partners, thereby conserving their mating time and energy; male–female attachment evolved to enable individuals to cooperate with a reproductive mate until species-specific parental duties have been completed. The evolution of these three emotion–motivation systems contribute to contemporary patterns of marriage, adultery, divorce, remarriage, stalking, homicide and other crimes of passion, and clinical depression due to romantic rejection. This article defines these three emotion–motivation systems. Then it discusses an ongoing project using functional magnetic resonance imaging of the brain to investigate the neural circuits associated with one of these emotion–motivation systems, romantic attraction.     

Complex‐valued analysis of arterial spin labeling–based functional magnetic resonance imaging signals

Cerebral blood flow‐dependent phase differences between tagged and control arterial spin labeling images are reported. A biophysical model is presented to explain the vascular origin of this difference. Arterial spin labeling data indicated that the phase difference is largest when the arterial component of the signals is preserved but is greatly reduced as the arterial contribution is suppressed by postinversion delays or flow‐crushing gradients. Arterial vasculature imaging by saturation data of activation and hypercapnia conditions showed increases in phase accompanying blood flow increases. An arterial spin labeling functional magnetic resonance imaging study yielded significant activation by magnitude‐only, phase‐only, and complex analyses when preserving the whole arterial spin labeling signal. After suppression of the arterial signal by postinversion delays, magnitude‐only and complex models yielded similar activation levels, but the phase‐only model detected nearly no activation. When flow crushers were used for arterial suppression, magnitude‐only activation was slightly lower and fluctuations in phase were dramatically higher than when postinversion delays were used. Although the complex analysis performed did not improve detection, a simulation study indicated that the complex‐valued activation model exhibits combined magnitude and phase detection power and thus maximizes sensitivity under ideal conditions. This suggests that, as arterial spin labeling imaging and image correction methods develop, the complex‐valued detection model may become helpful in signal detection. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.