The pathophysiology of prospective memory failure after diffuse axonal injury - Lesion-symptom analysis using diffusion tensor imaging

<p>Abstract</p> <p>Background</p> <p>Prospective memory (PM) is one of the most important cognitive domains in everyday life. The neuronal basis of PM has been examined by a large number of neuroimaging and neuropsychological studies, and it has been suggested that several cerebral domains contribute to PM. For these activation studies, a constellation of experimental PM trials was developed and adopted to healthy subjects. In the present study, we used a widely used clinical PM assessment battery to determine the lesions attributable to PM failure, with the hypothesis that lesion-symptom analysis using diffusion tensor imaging (DTI) in subjects with diffuse axonal injury (DAI) can reveal the neuronal basis of PM in everyday life.</p> <p>Results</p> <p>Fourteen DAI patients (age: range of 18-36, median 24) participated in this study. PM failure was scored in the range of 0-6 using three sub-tests of the Rivermead Behavioural Memory Test. The PM scores of DAI patients were in the range of 2-6 (median 4.5, inter-quartile range 2.25). The severity of axonal injury following DAI was examined using fractional anisotropy (FA), one of the DTI parameters, at voxel level in each subject. We then obtained clusters correlated with PM failure by conducting voxel-based regression analysis between FA values and PM scores. Three clusters exhibited significant positive correlation with PM score, the left parahippocampal gyrus, left inferior parietal lobe, and left anterior cingulate.</p> <p>Conclusions</p> <p>This is the first lesion-symptom study to reveal the neuronal basis of PM using DTI on subjects with DAI. Our findings suggest that the neuronal basis of PM is in the left parahippocampal gyrus, left inferior parietal lobe, and/or left anterior cingulate. These findings are similar to those of previous activation studies with loading experimental PM tasks.</p

Serial Changes in Delayed Focal Hippocampal Lesions in Patients with Transient Global Amnesia

The etiology of transient global amnesia (TGA) is not well understood. MR studies, including studies using diffusion-weighted imaging (DWI), have been used to investigate the pathophysiology of TGA, and focal hippocampal lesions have been detected in some studies. The aim of this study was to investigate serial changes in MR images from the patients with TGA. In seven TGA patients, serial MRI scans (from the same day of the・ onset to several days after the, onset of symptoms) using a 1.5-T MR unit were prospectively evaluated. Iri four patients, the duration of TGA was over 12 hr. Three of those patients showed small punctate hippocampal hypersensitivity with decreased ADC values on DW images. These lesions were detected in the postacute phase (a time window of 24 - 48 hr after the onset of symptoms). In follow-up studies performed several days after the onset of symptoms, DWI lesions had disappeared in the subacute phase (7-10 days after the TGA episode). The delayed hippocampal lesion on DW images with 1.5-T MRI in patients with TGA appears to be associated with longer duration of symptoms, to persist for several days and to disappear in the chronic phase

Brain activations in errorless and errorful learning in patients with diffuse axonal injury: A functional MRI study

Primary objective: Errorless learning has been reported to be effective in the rehabilitation of patients with impaired cognitive functions following brain injury. This study compared brain activations in errorless learning (EL) and errorful learning (EF) in patients with diffuse axonal injury (DAI) using a functional magnetic resonance imaging (fMRI). Methods and procedures: The participants were 13 patients with DAI. Thirteen healthy individuals were evaluated as a control group. The participants learned words under the EL and EF conditions in advance and performed the recognition task during fMRI scanning. Main outcomes and results: EL in the control group was significantly faster than EF (p = 0.005), but not in the DAI group. EL in the DAI group scored significantly higher than EF (p = 0.026). An fMRI showed significant activations in the posterior cingulate gyrus (BA 31) and precuneus (BA 7) in the control group when EF EL, but in the precuneus (BA 7, 31) and bilateral inferior parietal lobules (BA 39, 40) in the DAI group. Conclusions: These results indicate the disadvantage of EF and advantage of EL to DAI patients. The findings also reflect brain plasticity in patients with DAI in the chronic phase

Fabrication and Microstructure Tuning of a Pyrimidine-Bridged Organoalkoxysilane Membrane for CO₂ Separation

A novel pyrimidine-bridged organoalkoxysilane membrane was developed from 4,6-bis­(3-(triethoxysilyl)-1-propoxy)-1,3-pyrimidine (BTPP) via a sol–gel process. Self-catalyzed and HCl-catalyzed BTPP sols with different water molar ratios were prepared for membrane formation to tailor the microstructure of the BTPP membranes. A higher water molar ratio for the HCl-catalyzed sols led to the formation of a silica network with improved porosity and a well-connected structure. Gas adsorption measurements indicated that BTPP xerogels tended to show a dense silica network due to an organic-rich hybrid structure, and these also showed a higher level of CO₂/N₂ selectivity due to the presence of pyrimidine groups that could conduct special interactions with CO₂. Single-gas permeation testing was performed at different permeation temperatures using gases with different kinetic diameters: He (2.6 Å), H₂ (2.89 Å), CO₂ (3.3 Å), N₂ (3.64 Å), CH₄ (3.8 Å), and SF₆ (5.5 Å). The BTPP membranes showed a sharp kinetic diameter dependence of gas permeance with a higher level of H₂/SF₆ selectivity (>500). In addition, the relatively dense silica network and organic-rich properties of BTPP membranes resulted in activated diffusion for all gases considered, with the exception of SF₆ that could have permeated the BTPP membranes via larger pores or pinholes. CO₂ transport behaviors through BTPP membranes were compared according to activation energies for the permeation (<i>E</i>_p) of CO₂ and by the differences in <i>E</i>_p between CO₂ and N₂ (or CH₄). The BTPP-HCl-240 membrane that demonstrated the most-improved porosity and the best-connected silica network showed a lower <i>E</i>_p for CO₂ and a greater difference in <i>E</i>_p between CO₂ and N₂ (or CH₄). As a result, the BTPP-HCl-240 membrane exhibited great potential in CO₂ separation performance for both CO₂ permeance and CO₂/gas permselectivity. Compared with most of the reported amine-functionalized silica-based membranes, BTPP membranes showed great potential in CO₂ separation performance, which could lead to applications in CO₂ separation processes