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Experience can affect human gray matter volume. The behavioral correlates of individual differences in such brain changes are not well understood. In a group of Swedish individuals studying Italian as a foreign language, we investigated associations among time spent studying, acquired vocabulary, baseline performance on memory tasks, and gray matter changes. As a way of studying episodic memory training, the language learning focused on acquiring foreign vocabulary and lasted for 10weeks. T1-weighted structural magnetic resonance imaging and cognitive testing were performed before and after the studies. Learning behavior was monitored via participants' use of a smartphone application dedicated to the study of vocabulary. A whole-brain analysis showed larger changes in gray matter structure of the right hippocampus in the experimental group (N=33) compared to an active control group (N=23). A first path analyses revealed that time spent studying rather than acquired knowledge significantly predicted change in gray matter structure. However, this association was not significant when adding performance on baseline memory measures into the model, instead only the participants' performance on a short-term memory task with highly similar distractors predicted the change. This measure may tap similar individual difference factors as those involved in gray matter plasticity of the hippocampus.

Accumulating evidence suggests that engagement in leisure activities is associated with favorable trajectories of cognitive aging, but little is known about brain changes related to both activities and cognition. White matter microstructure shows experience-dependent plasticity and declines in aging. Therefore, we investigated the role of change in white matter microstructure in the activities-cognition link. We used repeated assessments of engagement, perceptual speed, and white matter microstructure (probed with diffusion tensor imaging) in a population-based sample of individuals over 80 years without dementia (n = 442, Mage = 85.1; n = 70 for diffusion tensor imaging; 2 occasions 3 years apart). Using multivariate latent change modeling, we observed positive correlations among changes in predominantly social activities, white matter microstructure, and perceptual speed. Interindividual differences in change in white matter microstructure statistically accounted for the association between change in leisure activities and change in perceptual speed. However, as analyses are based on observational data from 2 measurement occasions, causality remains unclear.

SummaryThe question of how we experience ownership of an entire body distinct from the external world is a fundamental problem in psychology and neuroscience [1–6]. Earlier studies suggest that integration of visual, tactile, and proprioceptive information in multisensory areas [7–11] mediates self-attribution of single limbs. However, it is still unknown how ownership of individual body parts translates into the unitary experience of owning a whole body. Here, we used a “body-swap” illusion [12], in which people experienced an artificial body to be their own, in combination with functional magnetic resonance imaging to reveal a coupling between the experience of full-body ownership and neural responses in bilateral ventral premotor and left intraparietal cortices, and left putamen. Importantly, activity in the ventral premotor cortex reflected the construction of ownership of a whole body from the parts, because it was stronger when the stimulated body part was attached to a body, was present irrespective of whether the illusion was triggered by stimulation of the hand or the abdomen, and displayed multivoxel patterns carrying information about full-body ownership. These findings suggest that the unitary experience of owning an entire body is produced by neuronal populations that integrate multisensory information across body segments.

Magnetic susceptibility provides an important contrast mechanism for MRI. Increasingly, susceptibility-based contrast is being exploited to investigate brain tissue microstructure and to detect abnormal levels of brain iron as these have been implicated in a variety of neuro-degenerative diseases. However, it remains unclear to what extent magnetic susceptibility-related contrast at high field relates to actual brain iron concentrations. In this study, we performed susceptibility weighted imaging as a function of field strength on healthy brains in vivo and post-mortem brain tissues at 1.5 T, 3 T and 7 T. Iron histology was performed on the tissue samples for comparison. The calculated susceptibility-related parameters R(2)(*) and signal frequency shift in four iron-rich regions (putamen, globus pallidus, caudate, and thalamus) showed an almost linear dependence (r>or=0.90 for R(2)(*); r>or=0.83 for phase, p

Diffusion tensor mapping with MRI can noninvasively track neural connectivity and has great potential for neural scientific research and clinical applications. For each diffusion tensor imaging (DTI) data acquisition scheme, the diffusion tensor is related to the measured apparent diffusion coefficients (ADC) by a transformation matrix. With theoretical analysis we demonstrate that the noise performance of a DTI scheme is dependent on the condition number of the transformation matrix. To test the theoretical framework, we compared the noise performances of different DTI schemes using Monte-Carlo computer simulations and experimental DTI measurements. Both the simulation and the experimental results confirmed that the noise performances of different DTI schemes are significantly correlated with the condition number of the associated transformation matrices. We therefore applied numerical algorithms to optimize a DTI scheme by minimizing the condition number, hence improving the robustness to experimental noise. In the determination of anisotropic diffusion tensors with different orientations, MRI data acquisitions using a single optimum b value based on the mean diffusivity can produce ADC maps with regional differences in noise level. This will give rise to rotational variances of eigenvalues and anisotropy when diffusion tensor mapping is performed using a DTI scheme with a limited number of diffusion-weighting gradient directions. To reduce this type of artifact, a DTI scheme with not only a small condition number but also a large number of evenly distributed diffusion-weighting gradients in 3D is preferable.

BOLD (blood oxygenation level-dependent) and FAIR (flow-sensitive alternating inversion recovery) imaging techniques were used to investigate the oxygenation and hemodynamic responses of human brain during repeated challenges of breath holding and prolonged single breath holding. The effects of different breathing techniques on BOLD and FAIR image contrasts were carefully examined. With a periodic breath-holding paradigm of 30 s, global changes in gray matter were observable both in T*2-weighted and FAIR images. T*2-weighted images showed 1-4% relative signal intensity increases, while FAIR images demonstrated relative cerebral blood flow (CBF) increase up to 30-70%. The activated pixels depicted in FAIR images were about three times less than those seen in T*2-weighted images. With prolonged breath holding, it was observed that signal intensities in T*2-weighted and FAIR images were dependent on the breathing techniques used. Breath holding after expiration gave rise to immediate signal intensity increases in T*2-weighted and FAIR images, whereas breath holding performed after deep inspiration signals showed a biphasic change both in flow and T*2-weighted. T*2-weighted and FAIR signals showed a transient decrease before rising above the baseline level.

Retention aid systems are commonly used in the papermaking process to flocculate the fine matericals in cellulose fiber suspensions. The addition of polymeric flocculants such as cationic polyacrylamide (C-PAM) also increases the fiber flocculation and the shear strength of the fiber flocs. The break-up process of fiber flocs in highly turbulent flow is of great importance to produce paper with an even fiber distribution. In this study, phase flow encoded nuclear magnetic resonance (NMR) imaging was used to study the pipe flow behavior of cellulose fiber suspensions when cationic polyacrylamide had been added. Axial velocity profiles were measured at different mean bulk flow rates. The mean velocity profiles for turbulent flow were analyzed in terms of the power-law. It was demonstrated that at low shear rates the polymeric flocculant induces phase separation in a dilute fiber suspension, while at high shear rates, polymer induced flocculation reduces turbulent intensities of the flow. Flow encoded NMR images were recorded for the fully turbulent flow of a 0.5 wt.% hardwood fiber suspension at different times (0.5–9.0 min) after polymer addition. Immediately after addition a steady plug flow profile was observed. After 9 min the flow is fully turbulent. This indicates that the polymer macromolecules are disrupted quickly in turbulent flow.

Flow behaviour of aqueous polyacrylamide solutions in a straight circular pipe of 26.2 mm in diameter was investigated by using phase flow encoded nuclear magnetic resonance imaging (NMRI). Premixed polyacrylamide solutions of four different concentrations. i.e. 1 000, 500, 300, and 200 wt. ppm were studied. The mean axial velocity profiles of the dilute polyacrylamide solutions were measured at various mean bulk flow rates up to 800 mm s−1. Laminar flows to unsteady turbulent flows through a transition flow regime were observed. For turbulent flows, the mean velocity profiles and the streamwise turbulence intensities were obtained by using a time-averaged NMRI method. The rheological behavior of the polyacrylamide solutions, that is the shear stress dependence on the shear rate, was also characterized by using the velocity profile data from NMRI together with pressure drop measurements. The results were compared with independently measured rheological data from a cone-and-plate viscometer.

Fiber suspensions of different types of wood pulp were studied by using the pulsed gradient spin-echo NMR technique. Water in pores inside the fibers can be discriminated from bulk water by using this method, since the diffusion of fiber water is restricted when the diffusion time is sufficiently long. The amount of fiber water in a suspension is linearly correlated to the fiber concentration of the suspension. From this linear correlation, the average pore volume of the pulp fibers studied was rigorously estimated to be 1.6 ± 0.3 cm 3 /g of cellulose fibers, which independently confirmed the results from solute exclusion studies. Furthermore, the self-diffusion coefficients of bulk water and fiber water were also determined. The self-diffusion coefficient of bulk water shows a concentration dependence due to the obstruction and hydration effects, but the self-diffusion coefficient of fiber water is constant in the concentration range studied.

The self-diffusion of water sorbed in wood pulp cellulose fibers was studied by using the pulsed gradient spin-echo (PGSE) method. The observed echo attenuation profiles deviate significantly from those of bulk liquids and can be decomposed into two components: one with a self-diffusion coefficient independent of the diffusion time, and one with an apparent diffusion coefficient that depends on the diffusion time. The relative amplitude of these two components for the different diffusion times used in the PGSE experiment is nearly constant. We attribute the two components to bulk water between cellulose fibers and to water in pores within the fibers, respectively. From the relative amplitude of the components and the known water content in the samples, the amount of water in pores inside the fibers was calculated to 1.4 g/g of cellulose fibers. The self-diffusion coefficient of the bulk water between the fibers is lower than that of neat water. This reduction is mainly caused by the obstruction effect of the cellulose fibers whereas the hydration effect is of minor importance. The apparent self-diffusion coefficient of water trapped in pores inside fibers is approximately one-third of that of the bulk water between fibers when the diffusion time is 12 ms and is reduced further by another factor of 3 when the diffusion time is increased to 80 ms. By using a sheet sample and applying the magnetic field gradient perpendicular or parallel to the sheet it was found that the diffusional motion of water in pores is anisotropic. These results indicate that the pores are elongated along the fiber axis having lengths ranging from a few micrometers up to 20 μm.

The authors regret that the following corrections were left off the original manuscripts: 1. Page 1263, Eq. (1) should be: y 1⁄4 14:62 1− exp −0:04x ð Þ f g þ 4:6 2. Page 1263, right column, in the paragraph that starts with: “Fig. 7A shows the relationship between...”, the sentence “The best-fit lines to the data are given by:...” should be written as: The best fit lines to the data are given by: y=0.058x+10.75 (at 1.5 T), y=0.120x+14.12 (at 3 T) and y=0.319x+19.79 (at 7 T), where x is the iron concentration in ppm and y is the R2⁎ in Hz. 3. Page 1264, Fig. 7(A). The three fitted equations should be: y 1⁄4 0:319xþ 19:79 y 1⁄4 0:120xþ 14:12 y 1⁄4 0:058xþ 10:75 4. Page 1266, Acknowledgments should be: We thank Dr. Matusuda Kant, M.D., Ph.D. and Suan Fulton The authors would like to apologise for any inconvenience caused.