Sources of pain related responses to posterior tibial nerve stimulation

Brain responses to posterior tibial nerve stimulation were examined in patients who suffered from a proven neuropathic (traumatic) pain. The aim of this study was to learn if these responses could be used for the assessment of persistent pain and its relief in chronic pain patients. Experiments were carried out in five patients, where usual strategies had failed and spinal cord stimulation was applied. It was found that the measured evoked responses, when these patients were in pain, showed additional waves at latencies at around 110 ms and 150 ms after stimulation of the posterior tibial nerve. The magnetic field and electrical potential distributions at these latencies were dipolar and the responses at 110 ms and 150 ms could be ascribed to two equivalent current dipoles situated in two distinct areas in the brain. In patients, who underwent spinal cord stimulation, the additional wave disappeared once the patient was in a pain free condition. For this group of patients the additional waves appear to be related to the perception of pain and this may offer an objective method to assess this kind of pain and study the effects of spinal cord stimulation. Although not mentioned here, similar results were found for median nerve stimulation

The particle-in-cell model for ab initio thermodynamics: implications for the elastic anisotropy of the Earth's inner core

We assess the quantitative accuracy of the particle-in-cell (PIC) approximation used in recent ab initio predictions of the thermodynamic properties of hexagonal-close-packed iron at the conditions of the Earth's inner core. The assessment is made by comparing PIC predictions for a range of thermodynamic properties with the results of more exact calculations that avoid the PIC approximation. It is shown that PIC gives very accurate results for some properties, but that it gives an incorrect treatment of anharmonic lattice vibrations. In addition, our assessment does not support recent PIC-based predictions that the hexagonal c/a ratio increases strongly with increasing temperature, and we point out that this casts doubt on a proposed re-interpretation of the elastic anisotropy of the inner core.Comment: 25 pages, 9 figures, submitted to Physics of the Earth and Planetary Interior

The axial ratio of hcp iron at the conditions of the Earth's inner core

We present ab initio calculations of the high-temperature axial c/a ratio of hexagonal-close-packed (hcp) iron at Earth's core pressures, in order to help interpret the observed seismic anisotropy of the inner core. The calculations are based on density functional theory, which is known to predict the properties of high-pressure iron with good accuracy. The temperature dependence of c/a is determined by minimising the Helmholtz free energy at fixed volume and temperature, with thermal contributions due to lattice vibrations calculated using harmonic theory. Anharmonic corrections to the harmonic predictions are estimated from calculations of the thermal average stress obtained from ab initio molecular dynamics simulations of hcp iron at the conditions of the inner core. We find a very gradual increase of axial ratio with temperature. This increase is much smaller than found in earlier calculations, but is in reasonable agreement with recent high-pressure, high-temperature diffraction measurements. This result casts doubt on an earlier interpretation of the seismic anisotropy of the inner core

Application of activated barrier hopping theory to viscoplastic modeling of glassy polymers

YesAn established statistical mechanical theory of amorphous polymer deformation has been incorporated as a plastic mechanism into a constitutive model and applied to a range of polymer mechanical deformations. The temperature and rate dependence of the tensile yield of PVC, as reported in early studies, has been modeled to high levels of accuracy. Tensile experiments on PET reported here are analyzed similarly and good accuracy is also achieved. The frequently observed increase in the gradient of the plot of yield stress against logarithm of strain rate is an inherent feature of the constitutive model. The form of temperature dependence of the yield that is predicted by the model is found to give an accurate representation. The constitutive model is developed in two-dimensional form and implemented as a user-defined subroutine in the finite element package ABAQUS. This analysis is applied to the tensile experiments on PET, in some of which strain is localized in the form of shear bands and necks. These deformations are modeled with partial success, though adiabatic heating of the instability causes inaccuracies for this isothermal implementation of the model. The plastic mechanism has advantages over the Eyring process, is equally tractable,and presents no particular difficulties in implementation with finite elements.F. Boutenel acknowledges an Erasmus Programme Scholarshi

Enhancing CBT for chronic insomnia: A randomised clinical trial of additive components of mindfulness or cognitive therapy

Although cognitive behavioural therapy (CBT) for insomnia has resulted in significant reductions in symptoms,most patients are not classified as good sleepers after treatment. The present study investigated whether additional sessions of cognitive therapy (CT) or mindfulness-based therapy (MBT) could enhance CBT in 64 participants with primary insomnia. All participants were given four sessions of standard CBT as previous research had identified this number of sessions as an optimal balance between therapist guidance and patient independence. Participants were then allocated to further active treatment (four sessions of CT or MBT) or a no further treatment control. The additional treatments resulted in significant improvements beyond CBT on self-report and objective measures of sleep and were well tolerated as evidenced by no dropouts from either treatment. The effect sizes for each of these additional treatments were large and clinically significant. The mean scores on the primary outcome measure, the Insomnia Severity Index, were 5.74 for CT and 6.69 for MBT, which are within the good-sleeper range. Treatment effects were maintained at follow-up. There were no significant differences between CT and MBT on any outcome measure. These results provide encouraging data on how to enhance CBT for treatment of insomnia

Effective insomnia treatments: Investigation of processes in mindfulness and cognitive therapy

Understanding the underlying mechanisms of recovery from insomnia is an important goal for improving existing treatments. In a randomised controlled trial, 57 participants with insomnia disorder were given either cognitive therapy (CT) or mindfulness-based therapy (MBT) following 4 sessions of CBT. Each participant was assessed on process measures related to CT and MBT. MBT resulted in improvement on mindfulness process measures and the size of the improvement was significantly greater than achieved in the CT condition. Interestingly, CT and MBT both resulted in significant improvement on the cognitive process measures. Treatment outcome on the primary outcome measure (Insomnia Severity Index) was not predicted by type of treatment but was predicted by posttreatment scores on the cognitive process measures. The results suggest that changes in cognitive processes are especially important in treating insomnia, and that there are different therapeutic modalities through which this can be achieved

Whole-head MEG analysis of cortical spatial organization from unilateral stimulation of median nerve in both hands: no complete hemispheric homology

We examined the contralateral hemispheric cortical activity in MEG (151 ch) after unilateral median nerve stimulation of the right and left hand in twenty healthy right-handed subjects. The goal was to establish parameters to describe cortical activity of the hemispheric responses and to study the potential ability to assess differences in volunteers and patients. We focused on the within-subject similarity and differences between evoked fields in both hands. Cortical activity was characterized by the overlay display of waveforms (CWP), number of peak stages, loci of focal maxima and minima in each stage, 3D topographic maps and exemplified equivalent current dipole characteristics. The paired-wise test was used to analyze the hemispheric differences. The waveform morphology was unique across the subjects, similar CWPs were noted in both hemispheres of the individual. The contralateral hemispheric responses showed a well defined temporal–spatial activation of six to seven stages in the 500 ms window. Consistently (in over 80% of subjects), the six stages across the subjects were 20M, 30M, 50M, 70M, 90M, and 150M. A 240M was present in the left hemisphere (LH) in 15/20 subjects and in the right hemisphere (RH) in 10/20. Statistics of the latencies and amplitudes of these seven stages were calculated. Our results indicated that the latency was highly consistent and exhibited no statistical mean difference for all stages. Furthermore, no mean amplitude differences between both hemispheres at each stage were found. The patterns of magnetic fields in both hemispheres were consistent in 70% of the subjects. A laterality index (L.I.) was used for defining the magnetic field amplitude differences between two hemispheres for each individual. Overall, the absolute amplitude of the brain responses was larger in the left than in the right hemisphere in the majority of subjects (16/20), yet a significant portion (4/20) exhibited right dominance of the N20m activity. Each individual exhibited a unique CWP, there was reliable consistency of peak latencies and mean amplitudes in median nerve MEG. Nevertheless, this study indicates the limitations of using the intact hemisphere responses to compare with those from the affected (brain) side and suggests caution in assuming full homology in the cortical organization of both hemispheres. This study provides some results to address clinical issues like which parameter describes individual differences best. Whether a genuine difference is found or whether any difference may simply represent the variability encountered in a normal population