Associations between gait speed and brain structure in amnestic mild cognitive impairment: a quantitative neuroimaging study.

BACKGROUND: Patients with amnestic mild cognitive impairment (aMCI) present gait disturbances including slower speed and higher variability when compared to cognitively healthy individuals (CHI). Brain neuroimaging could explore higher levels of motor control. Our purpose was to look for an association between morphometrics and gait parameters in each group. We hypothesized that the relation between morphological cerebral alteration and gait speed are different following the group. METHODS: Fifty-three participants (30 with aMCI and 23 CHI) were recruited in this French cross-sectional study (mean 72 ± 5 years, 38% female). Gait speed and gait variability (coefficients of variation of stride time (STV) and stride length (SLV)) were measured using GAITrite® system. CAT12 software was used to analyse volume and surface morphometry like gray matter volume (GMV) and cortical thickness (CT). Age, gender and education level were used as potential cofounders. RESULTS: aMCI had slower gait speed and higher STV when compared to CHI. In aMCI the full adjusted linear regression model showed that lower gait speed was associated with decreased GMV and lower CT in bilateral superior temporal gyri (p < 0.36). In CHI, no association was found between gait speed and brain structure. Higher SLV was correlated with reduced GMV in spread regions (p < 0.05) and thinner cortex in the middle right frontal gyrus (p = 0.001) in aMCI. In CHI, higher SLV was associated with reduced GMV in 1 cluster: the left lingual (p = 0.041). CONCLUSIONS: These findings indicate that lower gait speed is associated with specific brain structural changes as reduced GMV and CT during aMCI.

Specific age-correlated activation of top hierarchical motor control areas during gait-like plantar stimulation: An fMRI study.

A better understanding of gait disorders that are associated with aging is crucial to prevent adverse outcomes. The functional study of gait remains a thorny issue due to technical constraints inherent to neuroimaging procedures, as most of them require to stay supine and motionless. Using an MRI-compatible system of boots reproducing gait-like plantar stimulation, we investigated the correlation between age and brain fMRI activation during simulated gait in healthy adults. Sixty-seven right-handed healthy volunteers aged between 20 and 77 years old (49.2 ± 18.0 years; 35 women) were recruited. Two paradigms were assessed consecutively: (a) gait-like plantar stimulation and (b) chaotic and not gait-related plantar stimulation. Resulting statistical parametric maps were analyzed with a multiple-factor regression that included age and a threshold determined by Monte-Carlo simulation to fulfill a family-wise error rate correction of p < .05. In the first paradigm, there was an age-correlated activation of the right pallidum, thalamus and putamen. The second paradigm showed an age-correlated deactivation of both primary visual areas (V1). The subtraction between results of the first and second paradigms showed age-correlated activation of the right presupplementary motor area (Brodmann Area [BA] 6) and right mid-dorsolateral prefrontal cortex (BA9-10). Our results show age-correlated activity in areas that have been associated with the control of gait, highlighting the relevance of this simulation model for functional gait study. The specific progressive activation of top hierarchical control areas in simulated gait and advancing age corroborate a progressive loss of automation in healthy older adults.

Normal and pathological imaging of the hippocampus in geriatric patients.

The hippocampus is a small internal temporal cerebral structure which plays a primordial role in memory mechanisms. Magnetic resonance imaging (MRI) is the preferred method for analysing this structure. In older adults, dementia is the major cause of hippocampal anomalies, particularly atrophic anomalies, however, differential diagnoses involving other specific pathologies should also be recognised in this population. Most acute or recent hippocampal damage is detected based on MRI signal abnormalities. The aim of this article is to provide an iconographic review of normal and pathological hippocampal imaging in older adults with degenerative, infectious, vascular, inflammatory, tumoural, toxic, and metabolic disorders.

Vitamin D concentration and focal brain atrophy in older adults: a voxel-based morphometric study.

Vitamin D is involved in brain health and function. Our objective was to determine whether lower 25-hydroxyvitamin D (25OHD) concentration was associated with focal brain volume reduction in older adults. Serum 25OHD concentration was measured among 53 older adults (72 ± 5 years; 38% female; mean 25OHD = 67.3 ± 20.8 nmol/L). Gray matter volume (GMV) was automatically segmented using voxel-based morphometry with CAT12 software. Covariables were age, gender, education, total intracranial volume, and season. Serum 25OHD was positively associated with GMV in left calcarine sulcus (P < 0.05, TFCE, FWE-corrected). We found atrophy of the calcarine sulcus with lower 25OHD concentrations in older adults.

(Re)organisation of the somatosensory system after early brain lesion: A lateralization index fMRI study.

OBJECTIVE: To evaluate the relationship between neural (re)organization of the somatosensory cortex and impairment of sensory function (2-point discrimination [2PD]) in individuals with unilateral cerebral palsy. METHODS: We included 21 individuals with unilateral cerebral palsy. 2PD thresholds were evaluated on thumb pads, and activation of the somatosensory cortex was recorded by functional MRI (fMRI) during passive movements of the affected hand. A lateralization index (LI) was calculated for the primary sensory (S1) and secondary sensory (S2) cortices and the correlation between the LI and 2PD thresholds was analysed. RESULTS: We found a significant negative correlation between the 2PD thresholds and the S2 LI (r=-0.5, one-tailed P-value=0.01) and a trend towards a negative correlation with the S1 LI (r=-0.4, one-tailed P-value=0.05). CONCLUSION: High levels of activation in the contralesional hemisphere were associated with high levels of sensory impairment in individuals with unilateral cerebral palsy. The interhemispheric (re)organization of the somatosensory system may not effectively compensate for somatosensory impairment.

[Normal and pathological hippocampal imaging in geriatric patients]. / Imagerie normale et pathologique de l'hippocampe en gériatrie.

The hippocampus is a small internal temporal cerebral structure, which plays a primordial role in the mechanisms of memory. Magnetic resonance imaging (MRI) is the reference imaging modality for the hippocampal analysis. In older adults, dementia represents the majority of hippocampal diseases, but other specific pathologies must be known in the differential diagnosis. Many hippocampal abnormalities are represented by a loss of substance (atrophy). However, most acute or recent hippocampal damage is detected by MRI signal abnormalities. The aim of this article is to offer a pictorial review of the normal and pathological hippocampal aspects of older adults, during degenerative, infectious, vascular, inflammatory, tumoral, toxic and metabolic disorders.

Brain Activity during Mental Imagery of Gait Versus Gait-Like Plantar Stimulation: A Novel Combined Functional MRI Paradigm to Better Understand Cerebral Gait Control.

Human locomotion is a complex sensorimotor behavior whose central control remains difficult to explore using neuroimaging method due to technical constraints, notably the impossibility to walk with a scanner on the head and/or to walk for real inside current scanners. The aim of this functional Magnetic Resonance Imaging (fMRI) study was to analyze interactions between two paradigms to investigate the brain gait control network: (1) mental imagery of gait, and (2) passive mechanical stimulation of the plantar surface of the foot with the Korvit boots. The Korvit stimulator was used through two different modes, namely an organized ("gait like") sequence and a destructured (chaotic) pattern. Eighteen right-handed young healthy volunteers were recruited (mean age, 27 ± 4.7 years). Mental imagery activated a broad neuronal network including the supplementary motor area-proper (SMA-proper), pre-SMA, the dorsal premotor cortex, ventrolateral prefrontal cortex, anterior insula, and precuneus/superior parietal areas. The mechanical plantar stimulation activated the primary sensorimotor cortex and secondary somatosensory cortex bilaterally. The paradigms generated statistically common areas of activity, notably bilateral SMA-proper and right pre-SMA, highlighting the potential key role of SMA in gait control. There was no difference between the organized and chaotic Korvit sequences, highlighting the difficulty of developing a walking-specific plantar stimulation paradigm. In conclusion, this combined-fMRI paradigm combining mental imagery and gait-like plantar stimulation provides complementary information regarding gait-related brain activity and appears useful for the assessment of high-level gait control.

Feasibility and validity of monitoring subarachnoid hemorrhage by a noninvasive MRI imaging perfusion technique: Pulsed Arterial Spin Labeling (PASL).

BACKGROUND AND PURPOSE: To evaluate the validity of pulsed arterial spin labeling (PASL) imaging with cerebral blood flow (CBF) quantification for monitoring subarachnoid hemorrhage (SAH); to describe changes in the perfusion signal in the absence of or following several classic complications. MATERIALS AND METHODS: Fifteen patients and 14 healthy volunteers were assigned to SAH and control populations, respectively. ASL imaging was performed three times: between Day 0 (D0, i.e., day of onset of SAH symptoms) and D3, between D7 and D9 and between D12 and D14. ASL points were classified as complicated (symptomatic vasospasm, intraparenchymal hematoma or severe intracranial hypertension) or uncomplicated. Perfusion and CBF maps were generated after automated processing. The inversion time (TI) was fixed at 1800 ms. RESULTS: CBF mean value of Day0-3 uncomplicated SAH patients (47 ± 11.7 mL/min/100g) was significantly higher than that of the volunteers (36.5 ± 7.6 mL/min/100g; P=0.014). In a case-by-case analysis, we observed a global or regional hypoperfusion pattern when SAH was complicated by vasospasm or severe intracranial hypertension, particularly at the junctional areas. Furthermore, we have faced major vascular artefacts, visible as serpiginous high signals and related to the retention of labeled protons in arteries concerning by angiographic vasospasm. CONCLUSION: PASL is an interesting perfusion technique to non-invasively highlight perfusion changes in complicated SAH and can provide a new element in the decision to perform urgent endovascular treatment. However, the increase in arterial transit time makes the Buxton quantification model inapplicable and leads to false high CBF values in the single-TI PASL technique.