Gray Matter Volume and Cognitive Performance During Normal Aging. A Voxel-Based Morphometry Study.

Normal aging is characterized by decline in cognitive functioning in conjunction with extensive gray matter (GM) atrophy. A first aim of this study was to determine GM volume differences related to aging by comparing two groups of participants, middle-aged group (MAG, mean age 41 years, N = 16) and older adults (OG, mean age 71 years, N = 14) who underwent an magnetic resonance images (MRI) voxel-based morphometry (VBM) evaluation. The VBM analyses included two optimized pipelines, for the cortex and for the cerebellum. Participants were also evaluated on a wide range of cognitive tests assessing both domain-general and language-specific processes, in order to examine how GM volume differences between OG and MAG relate to cognitive performance. Our results show smaller bilateral GM volume in the OG relative to the MAG, in several cerebral and right cerebellar regions involved in language and executive functions. Importantly, our results also revealed smaller GM volume in the right cerebellum in OG relative to MAG, supporting the idea of a complex cognitive role for this structure. This study provides a broad picture of cerebral, but also cerebellar and cognitive changes associated with normal aging.

Track-weighted imaging for neuroretina: Evaluations in healthy volunteers and ischemic optic neuropathy.

BACKGROUND: The use of MRI-tractography to explore the human neuroretina is yet to be reported. Track-weighted imaging (TWI) was recently introduced as a qualitative tractography-based method with high anatomical contrast. PURPOSE: To explore the human retina in healthy volunteers and patients with anterior ischemic optic neuropathy (AION) using TWI reconstructions. STUDY TYPE: Prospective. POPULATION: Twenty AION patients compared with 20 healthy volunteers. FIELD STRENGTH/SEQUENCE: 3.0T MRI diffusion-weighted imaging (DWI) with b-value of 1000 s/mm2 and 60 diffusion-weighting noncollinear directions. ASSESSMENT: We performed constrained spherical deconvolution from the diffusion-weighted signal and volumetric tractography method, whereby 10 million streamlines are initiated from seed points randomly distributed throughout the orbital area. We then reconstructed TWI maps with isotropic voxel size of 300 µm. STATISTICAL TESTS: We tested the effect of the number of diffusion-weighting directions, ocular laterality, and ocular dominance on healthy retinal fascicles distribution. We then performed factorial analysis of variance to test the effects of the presence/absence of the fascicles on the visual field defect in patients. RESULTS: In healthy volunteers, we found more temporal fascicle in right eyes (P = 0.001), more superior fascicles in dominant eyes (P = 0.014), and fewer fascicles with tractography maps based on 30 directions than those based on 45 directions (P = 9 × 10-8 ) and 60 directions (P = 6 × 10-7 ). Eight out of 20 AION patients presented with complete absence of neuroretinal fascicle, side of the disease, which was correlated with visual field mean deviation at the 6-month visit [F(1,17) = 6.97, P = 0.016]. Seven patients presented with a temporal fascicle in the injured eye; this fascicle presence was linked to visual field mean deviation at the 6-month visit [F(1,17) = 8.43, P = 0.009]. DATA CONCLUSION: In AION patients, the presence of the temporal neuroretinal fascicle in the affected eye provides an objective outcome radiological sign correlated with visual performance. LEVEL OF EVIDENCE: 2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018.

Behavioral evidence for a differential modulation of semantic processing and lexical production by aging: a full linear mixed-effects modeling approach.

The effect of normal aging on lexical production and semantic processing was evaluated in 72 healthy participants. Four tasks were used, picture naming (PN), picture categorization (PC), numerical judgment (NJ), and color judgment (CJ). The dependence of reaction time (RT) and correct responses with age was accounted by mixed-effects models. Participants underwent neuropsychological testing for verbal, executive, and memory functions. The RTs increase significantly with age for all tasks. After parceling out the non-specific cognitive decline, as reflected by the NJ task, the RT for the PN task decreases with age. Behavioral data were interpreted in relation with neuropsychological scores. Our results suggest that (a) naming becomes more automatic and semantic processing slightly more difficult with age, and (b) a non-specific general slowdown of cognitive processing occurs with age. Lexical production remained unaltered, based on compensatory automatic processes. This study also suggests a possible slowdown of semantic processing, even in normal aging.

Aging Modulates the Hemispheric Specialization during Word Production.

Although older adults exhibit normal accuracy in performing word retrieval and generation (lexical production; e.g., object naming), they are generally slower in responding than younger adults. To maintain accuracy, older adults recruit compensatory mechanisms and strategies. We focused on two such possible compensatory mechanisms, one semantic and one executive. These mechanisms are reflected at inter- and intra-hemispheric levels by various patterns of reorganization of lexical production cerebral networks. Hemispheric reorganization (HR) changes were also evaluated in relation to increase naming latencies. Using functional magnetic resonance imaging (fMRI), we examined 27 healthy participants (from 30 years to 85 years) during an object naming task, exploring and identifying task-related patterns of cerebral reorganization. We report two main results. First, we observed a left intra-hemispheric pattern of reorganization, the left anterior-posterior aging (LAPA) effect, consisting of supplementary activation of left posterior (temporo-parietal) regions in older adults and asymmetric activation along the left fronto-temporal axis. This pattern suggests that older adults recruit posterior semantic regions to perform object naming. The second finding consisted of bilateral recruitment of frontal regions to maintain appropriate response times, especially in older adults who were faster performers. This pattern is discussed in terms of compensatory mechanism. We suggest that aging is associated with multiple, co-existing compensation and reorganization mechanisms and patterns associated with lexical production.

MRI of endolymphatic hydrops in patients with Meniere's disease: a case-controlled study with a simplified classification based on saccular morphology.

OBJECTIVES: Endolymphatic hydrops (EH) can be studied in patients by MRI. With the semi-quantitative grading system, previous imaging studies showed discrepancies in the occurrence and grading of EH in patients with Meniere's disease (MD). Here, we compared the inversion of the saccule to utricle area ratio (SURI) with the semi-quantitative method of grading conventionally used to diagnose MD. METHODS: Imaging was carried out on a 3-T MRI scanner. We performed 3D-FLAIR sequences 4 h after a single intravenous dose of contrast agent. Two radiologists independently studied the morphology of the inner ear structures in the healthy subjects and MD patients. Each subject was then graded on the basis of the EH semi-quantitative analysis and on saccular morphology using axial and sagittal reference slices in the vestibule plane. RESULTS: Thirty healthy subjects and 30 MD patients had MRI scans. Using the semi-quantitative method, we found no significant difference in the number of subjects with EH between the two groups. SURI was found in 15 out of 30 MD patients and in none of the 30 healthy subjects. In three MD patients the saccule was not visible. CONCLUSION: SURI is currently the most specific criterion for imaging diagnosis of MD. KEY POINTS: • Half of MD patients presented with inversion of the saccule to utricle ratio. • Saccular analysis is crucial when assessing patients with Meniere's disease. • In some patients, the saccule is not visible, suggestive of intra-labyrinthine fistulae.

The Self-Pleasantness Judgment Modulates the Encoding Performance and the Default Mode Network Activity.

In this functional magnetic resonance imaging (fMRI) study, we evaluated the effect of self-relevance on cerebral activity and behavioral performance during an incidental encoding task. Recent findings suggest that pleasantness judgments reliably induce self-oriented (internal) thoughts and increase default mode network (DMN) activity. We hypothesized that this increase in DMN activity would relate to increased memory recognition for pleasantly-judged stimuli (which depend on internally-oriented attention) but decreased recognition for unpleasantly-judged items (which depend on externally-oriented attention). To test this hypothesis, brain activity was recorded from 21 healthy participants while they performed a pleasantness judgment requiring them to rate visual stimuli as pleasant or unpleasant. One hour later, participants performed a surprise memory recognition test outside of the scanner. Thus, we were able to evaluate the effects of pleasant and unpleasant judgments on cerebral activity and incidental encoding. The behavioral results showed that memory recognition was better for items rated as pleasant than items rated as unpleasant. The whole brain analysis indicated that successful encoding (SE) activates the inferior frontal and lateral temporal cortices, whereas unsuccessful encoding (UE) recruits two key medial posterior DMN regions, the posterior cingulate cortex (PCC) and precuneus (PCU). A region of interest (ROI) analysis including classic DMN areas, revealed significantly greater involvement of the medial prefrontal cortex (mPFC) in pleasant compared to unpleasant judgments, suggesting this region's involvement in self-referential (i.e., internal) processing. This area may be responsible for the greater recognition performance seen for pleasant stimuli. Furthermore, a significant interaction between the encoding performance (successful vs. unsuccessful) and pleasantness was observed for the PCC, PCU and inferior frontal gyrus (IFG). Overall, our results suggest the involvement of medial frontal and parietal DMN regions during the evaluation of self-referential pleasantness. We discuss these results in terms of the introspective referential of pleasantness judgments and the differential brain modulation based on internally- vs. externally-oriented attention during encoding.

BOLD fMRI of cerebrovascular reactivity in the middle cerebral artery territory: A 100 volunteers' study.

BACKGROUND AND PURPOSE: The assessment of cerebrovascular reactivity (CVR) has shown promising results for its use in medical diagnosis and prognosis, especially in patients suffering from severe intracranial arterial stenosis. However, its quantification remains uncertain because of a large variability inherent in brain anatomy and in methodological settings. To overcome this variability, we provide lateralization index (LI) values for CVR within the middle cerebral artery territory to detect CVR impairment. MATERIALS AND METHODS: We assessed CVR in 100 volunteers (41 females; 47.52 ± 21.58 years) without cervico-encephalic arterial stenosis using BOLD-fMRI contrast with a block-design hypercapnic challenge. Averaged end-tidal CO2 was used as a physiological regressor for statistical analyses with a general linear model. We measured %BOLD signal-change in segmented gray matter regions of interest in the middle cerebral artery territory (MCA). We calculated a laterality index according to the following formula: LI=(CVRleft-CVRright)/(CVRleft+CVRright). We tested the effects of methodological settings (i.e. hypercapnic gas, gas administration means, MR acquisition and sex) on %BOLD signal change and LI values with analysis of variance. RESULTS: No adverse effects of the hypercapnic challenge were reported. LI values were independent of experimental conditions. Mean LI calculated in MCA territories was 0.016 ± 0.031, giving the lower and upper limits of 95% (m ± 2SD) of this population distribution at]-0.05; 0.08[. CONCLUSION: LI can effectively help us to overcome measurement variabilities. Therefore, it can be used to detect abnormal asymmetries in CVR and identify patients at higher risk of ischemic stroke.