Studying the neural bases of prism adaptation using fMRI:a technical and design challenge

Prism adaptation induces rapid recalibration of visuomotor coordination. The neural mechanisms of prism adaptation have come under scrutiny since the observations that the technique can alleviate hemispatial neglect following stroke, and can alter spatial cognition in healthy controls. Relative to non-imaging behavioral studies, fMRI investigations of prism adaptation face several challenges arising from the confined physical environment of the scanner and the supine position of the participants. Any researcher who wishes to administer prism adaptation in an fMRI environment must adjust their procedures enough to enable the experiment to be performed, but not so much that the behavioral task departs too much from true prism adaptation. Furthermore, the specific temporal dynamics of behavioral components of prism adaptation present additional challenges for measuring their neural correlates. We developed a system for measuring the key features of prism adaptation behavior within an fMRI environment. To validate our configuration, we present behavioral (pointing) and head movement data from 11 right-hemisphere lesioned patients and 17 older controls who underwent sham and real prism adaptation in an MRI scanner. Most participants could adapt to prismatic displacement with minimal head movements, and the procedure was well tolerated. We propose recommendations for fMRI studies of prism adaptation based on the design-specific constraints and our results

Correlation of Diffusion and Metabolic Alterations in Different Clinical Forms of Multiple Sclerosis

Diffusion tensor imaging (DTI) and MR spectroscopic imaging (MRSI) provide greater sensitivity than conventional MRI to detect diffuse alterations in normal appearing white matter (NAWM) of Multiple Sclerosis (MS) patients with different clinical forms. Therefore, the goal of this study is to combine DTI and MRSI measurements to analyze the relation between diffusion and metabolic markers, T2-weighted lesion load (T2-LL) and the patients clinical status. The sensitivity and specificity of both methods were then compared in terms of MS clinical forms differentiation. MR examination was performed on 71 MS patients (27 relapsing remitting (RR), 26 secondary progressive (SP) and 18 primary progressive (PP)) and 24 control subjects. DTI and MRSI measurements were obtained from two identical regions of interest selected in left and right centrum semioval (CSO) WM. DTI metrics and metabolic contents were significantly altered in MS patients with the exception of N-acetyl-aspartate (NAA) and NAA/Choline (Cho) ratio in RR patients. Significant correlations were observed between diffusion and metabolic measures to various degrees in every MS patients group. Most DTI metrics were significantly correlated with the T2-LL while only NAA/Cr ratio was correlated in RR patients. A comparison analysis of MR methods efficiency demonstrated a better sensitivity/specificity of DTI over MRSI. Nevertheless, NAA/Cr ratio could distinguish all MS and SP patients groups from controls, while NAA/Cho ratio differentiated PP patients from controls. This study demonstrated that diffusivity changes related to microstructural alterations were correlated with metabolic changes and provided a better sensitivity to detect early changes, particularly in RR patients who are more subject to inflammatory processes. In contrast, the better specificity of metabolic ratios to detect axonal damage and demyelination may provide a better index for identification of PP patients

The left ventral occipito-temporal response to words depends on language lateralization but not on visual familiarity.

International audienceThe sensitivity of the left ventral occipito-temporal (vOT) cortex to visual word processing has triggered a considerable debate about the role of this region in reading. One popular view is that the left vOT underlies the perceptual expertise needed for rapid skilled reading. Because skilled reading breaks down when words are presented in a visually unfamiliar format, we tested this hypothesis by analyzing vOT responses to horizontally presented words (familiar format) and vertically presented words (unfamiliar format). In addition, we compared the activity in participants with left and right cerebral dominance for language generation. Our results revealed 1) that the vOT activity during reading is lateralized to the same side as the inferior frontal activity during word generation, 2) that vertically and horizontally presented words triggered the same amount of activity in the vOT of the dominant hemisphere, but 3) that there was significantly more activity for vertically presented words in the vOT of the nondominant hemisphere. We suggest that the reading-related activity in vOT reflects the integration of general perceptual processes with language processing in the anterior brain regions and is not limited to skilled reading in the familiar horizontal format

''Absolute'' quantification in magnetic resonance spectroscopy: validation of a clinical protocol in multiple sclerosis

articleMRS allows to measure cerebral metabolites, thus helping to characterize brain disease diagnosis and followup. Metabolite concentration quantification is usually based on metabolite ratio referring to creatine. If this metabolite concentration is supposed to be constant, it may vary in pathological processes. Therefore, ``absolute'' concentration methodology is needed. The aim of this study is to validate a clinical ``absolute'' quantification protocol through the development of an external metabolic phantom, calibration and correction, and the investigation of reproducibility issues. When phantom stability was investigated by a short-term and a long-term reproducibility study, both Standard Deviations (SD) were in agreement with literature values. This ``absolute'' quantification method was applied to patients with Multiple Sclerosis (MS). The results show a significant decrease in both N-Acetyl Aspartate (NAA) and choline concentrations

Caregiving for Patients With Frontotemporal Dementia in Latin America

Latin America is a vast heterogeneous territory where chronic diseases such as mild cognitive impairment or dementia are becoming higher. Frontotemporal dementia (FTD) prevalence in this region is estimated to be around 12-18 cases per thousand persons. However, this prevalence is underestimated given the lack of awareness of FTD even among healthcare professionals. Family members are responsible for the care of patients with FTD at home. These caregivers deliver care despite being ill-equipped and living in the context of austerity policies and social inequities. They often face unsurmountable financial and social burdens that are specific to the region. The most important step to support caregivers in Latin America is to increase awareness of the disease at all levels. Healthcare diplomacy is fundamental to create joint efforts that push policies forward to protect caregivers of FTD patients

High-resolution myocardial perfusion mapping in small animals in vivo by spin-labeling gradient-echo imaging

An ECG and respiration-gated spin-labeling gradient-echo imaging technique is proposed for the quantitative and completely noninvasive measurement and mapping of myocardial perfusion in small animals in vivo. In contrast to snapshot FLASH imaging, the spatial resolution of the perfusion maps is not limited by the heart rate. A significant improvement in image quality is achieved by synchronizing the inversion pulse to the respiration movements of the animals, thereby allowing for spontaneous respiration. High-resolution myocardial perfusion maps (in-plane resolution=234 x 468 microm2) demonstrating the quality of the perfusion measurement were obtained at 4.7 T in a group of seven freely breathing Wistar-Kyoto rats under isoflurane anesthesia. The mean perfusion value (group average +/- SD) was 5.5 +/- 0.7 ml g(-1)min(-1). In four animals, myocardial perfusion was mapped and measured under cardiac dobutamine stress. Perfusion increased to 11.1 +/- 1.9 ml g(-1)min(-1). The proposed method is particularly useful for the study of small rodents at high fields

Subject-Specific Activation of Central Respiratory Centers during Breath-Holding Functional Magnetic Resonance Imaging

International audienceBackground: Voluntary breath-holding (BH) triggers responses from central neural control and respiratory centers in order to restore breathing. Such responses can be observed using functional MRI (fMRI). Objectives: We used this paradigm in healthy volunteers with the view to develop a biomarker that could be used to investigate disorders of the central control of breathing at the individual patient level. Method: In 21 healthy human subjects (mean age±SD, 32.8 ± 9.9 years old), fMRI was used to determine, at both the individual and group levels, the physiological neural response to expiratory and inspiratory voluntary apneas, within respiratory control centers in the brain and brainstem. Results: Group analysis showed that expiratory BH, but not inspiratory BH, triggered activation of the pontine respiratory group and raphe nuclei at the group level, with a significant relationship between the levels of activation and drop in SpO2. Using predefined ROIs, expiratory BH, and to a lesser extent, inspiratory BH were associated with activation of most respiratory centers. The right ventrolateral nucleus of the thalamus, right pre-Bötzinger complex, right VRG, right nucleus ambiguus, and left Kölliker-Fuse-parabrachial complex were only activated during inspiratory BH. Individual analysis identified activations of cortical/subcortical and brainstem structures related to respiratory control in 19 out of 21 subjects. Conclusion: Our study shows that BH paradigm allows to reliably trigger fMRI response from brainstem and cortical areas involved in respiratory control at the individual level, suggesting that it might serve as a clinically relevant biomarker to investigate conditions associated with an altered central control of respiration

Neurodegenerative Disease and the Experience of Homelessness.

Introduction: Today, half of the American homeless population is older than 50 years of age. This shift in age distribution among people experiencing homelessness has challenged our long-held views of the causes of homelessness. Age-related neurological diseases, especially neurodegenerative diseases of the brain (NDDB), may play a role eliciting homelessness in a significant proportion of vulnerable older adults. This article aims to explore relationships between homelessness and NDDB in a cohort of research participants enrolled in observational studies on NDDB at an academic center. Methods: We reviewed charts of the Memory and Aging Center (MAC) of the University of California, San Francisco's database searching for research participants with NDDB that had direct relationship to homelessness. We reviewed all research visits conducted between 2004 and 2018 (N = 5,300). Research participants who had any relationship to homelessness were included in this analysis. NDDB was diagnosed via comprehensive neurological, functional, neuropsychological, and biomarker assessments. Non-parametric tests were used for analysis. Thirteen participants were found to have a direct relationship with homelessness. Seven were female and the median of education was 16 (IR: 12.0-19.5) years. Participants were divided into two groups: Those who experienced homelessness while symptomatic from a NDDB but before formal diagnosis (n = 5, Group 1); and participants with formally diagnosed NDDB who exhibited a new propensity toward homelessness (n = 8, Group 2). Compared to Group 2, participants in Group 1 were younger (p = 0.021) and showed similar results in the neuropsychological evaluation. In both groups, the most prevalent diagnosis was frontotemporal dementia. In Group 1, the majority of participants became homeless in the setting of a fragile socioeconomic situation and informants believed that NDDB contributed or caused their homeless state. In Group 2, a new propensity toward homelessness became manifest in different ways and it stood out that all of these participants were well-supported by family and friends during their illness. Conclusions and Relevance: This case series highlights the role that NDDB may have in precipitating homelessness among vulnerable older adults, particularly in the setting of challenging socioeconomic circumstances and unsupportive living environments. Social ramifications of these findings, particularly pertaining to challenges around rehousing these individuals is discussed

Caracterisation de la substance blanche apparement normale dans la sclerose en plaques par IRM de tenseur de diffusion

articl