Do you see what I see? Sex differences in the discrimination of facial emotions during adolescence

During adolescence social relationships become increasingly important. Establishing and maintaining these relationships requires understanding of emotional stimuli, such as facial emotions. A failure to adequately interpret emotional facial expressions has previously been associated with various mental disorders that emerge during adolescence. The current study examined sex differences in emotional face processing during adolescence. Participants were adolescents (n = 1951) with a target age of 14, who completed a forced-choice emotion discrimination task. The stimuli used comprised morphed faces that contained a blend of two emotions in varying intensities (11 stimuli per set of emotions). Adolescent girls showed faster and more sensitive perception of facial emotions than boys. However, both adolescent boys and girls were most sensitive to variations in emotion intensity in faces combining happiness and sadness, and least sensitive to changes in faces comprising fear and anger. Furthermore, both sexes overidentified happiness and anger. However, the overidentification of happiness was stronger in boys. These findings were not influenced by individual differences in the level of pubertal maturation. These results indicate that male and female adolescents differ in their ability to identify emotions in morphed faces containing emotional blends. The findings provide information for clinical studies examining whether sex differences in emotional processing are related to sex differences in the prevalence of psychiatric disorders within this age group.

Combined white matter imaging suggests myelination defects in visual processing regions in schizophrenia

Diverse pathological changes occur in the white matter (WM) of patients with schizophrenia. Various microstructural alterations including a reduction in axonal number or diameter, reduced myelination, or poor coherence of fibers could account for these changes. Abnormal integrity of macromolecules such as myelin ('dysmyelination') can be studied by applying multiple modalities of WM imaging such as diffusion tensor imaging (DTI) and magnetization transfer imaging (MTI) in parallel. Using ultra-high field (7 Tesla) MTI in 17 clinically stable patients with schizophrenia and 20 controls, we evaluated the voxelwise distribution of macromolecular WM abnormalities. Patients had a significant reduction in magnetization transfer ratio (MTR) in WM adjacent to visual processing regions and inferior temporal cortex (Cohen's d=1.54). Among the regions showing MTR reduction, a concurrent reduction in fractional anisotropy (FA) occurs proximal to the lingual gyrus. Multiple regression analysis revealed that the degree of FA reduction in the putatively 'dysmyelinated' regions in patients predicted impaired processing speed (PS; β=0.74; P=0.003), a core cognitive dysfunction in schizophrenia. In controls, MTR/FA in the occipito-temporal regions were not associated with PS. Our findings suggest that dysmyelination in visual processing regions is present in patients with schizophrenia with greatest cognitive and functional impairment. Combined DTI/MTI deficits in the occipito-temporal region may be an important variable when considering potential treatment targets for improving cognitive function in schizophrenia.

Cortical lesion load correlates with diffuse injury of multiple sclerosis normal appearing white matter

BACKGROUND

Degeneration of central nervous system normal appearing white matter (NAWM) underlies disability and progression in multiple sclerosis (MS). Axon loss typifies NAWM degeneration.

OBJECTIVE

The objective of this paper is to assess correlation between cortical lesion load and magnetisation transfer ratio (MTR) of the NAWM in MS. This was in order to test the hypothesis that cortical lesions cause NAWM degeneration.

METHODS

Nineteen patients with MS underwent 7 Tesla magnetisation-prepared-rapid-acquisition-gradient-echo (MPRAGE), and magnetisation transfer ratio (MTR) brain magnetic resonance imaging (MRI). Cortical lesions were identified using MPRAGE and MTR images of cortical ribbons. White matter lesions (WMLs) were segmented using MPRAGE images. WML maps were subtracted from white matter volumes to produce NAWM masks. Pearson correlation was calculated for NAWM MTR vs cortical lesion load, and WML volumes.

RESULTS

Cortical lesion volumes and counts all had significant correlation with NAWM mean MTR. The strongest correlation was with cortical lesion volumes obtained using MTR images (r = -0.6874, p = 0.0006). WML volume had no significant correlation with NAWM mean MTR (r = -0.08706, p = 0.3615).

CONCLUSION

Our findings are consistent with the hypothesis that cortical lesions cause NAWM degeneration. This implicates cortical lesions in the pathogenesis of NAWM axon loss, which underpins long-term disability and progression in MS.

Exposure classification of MRI workers in epidemiological studies

We estimate that there are about 100,000 workers from different disciplines, such as radiographers, nurses, anesthetists, technicians, engineers, etc., who can be exposed to substantial electromagnetic fields (compared to normal background levels) around magnetic resonance imaging (MRI) scanners. There is a need for well-designed epidemiological studies of MRI workers but since the exposure from MRI equipment is a very complex mixture of static magnetic fields, switched gradient magnetic fields, and radiofrequency electromagnetic fields (RF EMF), it is necessary to discuss how to assess the exposure in epidemiological studies. As an alternative to the use of job title as a proxy of exposure, we propose an exposure categorization for the different professions working with MRI equipment. Specifically, we propose defining exposure in three categories, depending on whether people are exposed to only the static field, to the static plus switched gradient fields or to the static plus switched gradient plus RF fields, as a basis for exposure assessment in epidemiological studies.

Fatal outcome of a hepatitis B virus transfusion-transmitted infection

BACKGROUND AND OBJECTIVES

In 2008, hepatitis B virus (HBV) DNA testing was not yet mandatory for the screening of blood donations in Switzerland. At that time, HBsAg was the only specific mandatory marker for HBV. The importance of high sensitivity for HBV NAT screening is shown.

MATERIALS AND METHODS

Donor and recipient of a transfusion-transmitted HBV infection were followed up. Multiple samples were tested for HBV serological and molecular markers.

RESULTS

At donation, the donor appeared healthy, HBsAg was negative and had a normal ALAT level. Ten weeks later, clinical symptoms suggested acute HBV infection as was confirmed with positive HBsAg, HBeAg, anti-HBc IgG, anti-HBc IgM and anti-HBe. The archived sample from the original donation was negative for anti-HBc, but positive for HBV DNA (17 IU/ml). A recipient transfused with the red cell concentrate was HBV DNA positive (3100 IU/ml) 3 months post-transfusion. After five months, HBsAg, HBeAg, anti-HBc and HBV DNA (1.1 x 10(11) IU/ml) were positive. Two weeks later, the patient died from complications associated with HBV infection and his underlying bone marrow disease.

CONCLUSIONS

The present case illustrates the importance of introducing highly sensitive HBV NAT screening strategy to prevent possible HBV transfusion-transmitted infections from donors with low viral load.

The change in cerebrovascular reactivity between 3 T and 7 T measured using graded hypercapnia

Mapping cerebrovascular reactivity (CVR) to hypercapnia is important both clinically and for improved understanding of the haemodynamic properties of the BOLD effect. In this work, BOLD/R2 CVR was investigated by using a device which provided small, repeatable and stable steps in PETCO2, whilst maintaining a steady PETO2 level. Significant CVR was observed in both grey and white matter at both 3 and 7 T, whilst an approximately linear relationship found between R2 CVR and field strength has implications for BOLD models and calibration. Grey matter R2 CVR was 0.066+/-0.004 s(-1) mm Hg(-1) at 3 T and 0.141+/-0.008 s(-1) mm Hg(-1) at 7 T. White matter R2 CVR was 0.021+/-0.003 s(-1) mm Hg(-1) at 3 T and 0.040+/-0.007 s(-1) mm Hg(-1) at 7 T.

Investigating the effect of blood susceptibility on phase contrast in the human brain

Recent work has shown a dramatic contrast between GM and WM in gradient echo phase images at high field (7 T). Although this contrast is key to the exploitation of phase in imaging normal and pathological tissue, its origin remains contentious. Several sources for this contrast have been considered including iron content, myelin, deoxy-hemoglobin, or water-macromolecule interactions. Here we quantify the contribution of intravascular dHb to the GM/WM contrast in the human brain at 7 T by modulating the susceptibility of the blood using a paramagnetic contrast agent. By carrying out high resolution, dynamic, gradient echo imaging before, during and after the injection of the contrast agent, we were able to follow the change in GM/WM phase contrast and to monitor simultaneously the susceptibility of the blood. Using these data in conjunction with the known susceptibility of venous blood we estimate the upper bound for the relative contribution of dHb in the vasculature to the measured GM/WM phase contrast to be 0.48 Hz for GM close to the pial surface, and 0.27 Hz for deeper GM. These values are up to 20% of the GM/WM phase difference observed in the human brain at 7 T. Furthermore, we found that the fractional blood volume differences required to account for the observed GM/WM phase contrast are 1.3% and 0.7% for GM close to the pial surface and for deeper GM, respectively.

Phase vs. magnitude information in functional magnetic resonance imaging time series: toward understanding the noise

Although it has been shown that the phase of the MR signal from the brain is particularly prone to variation due to respiration, the overall physiological information contained in phase time series is not well understood. Here, we explore the different physiological processes contributing to the phase time series noise, identify their spatiotemporal characteristics and examine their relationship to BOLD-related and non-BOLD-related physiological noise in the magnitude time series. This was performed by manipulating the contribution of physiological noise to the total signal variance by modulating the TE and voxel volume, and using a short TR in order to adequately sample physiological signal fluctuations. The phase and magnitude signals were compared both before and after removal of signal fluctuations at the primary respiratory and cardiac frequencies with RETROICOR. We found that the temporal phase noise increased with TE at a faster rate than predicted by 1/TSNR as a result of physiological noise. As suggested by previous studies, the primary contributor to phase physiological noise was respiration-related effects which were manifested at a large scale (>1 cm). Notably, RETROICOR removed respiration-related large-scale artifacts and this resulted in considerable improvements in the temporal phase stability (7-90%). Physiological noise in the magnitude time series after RETROICOR consisted of low-frequency BOLD-related fluctuations (<0.13 Hz) localized to gray matter and the vasculature, and fluctuations in the vasculature correlated with slow (<0.1 Hz) variations in respiration volume and cardiac rhythm. Physiological noise in the phase signal after RETROICOR also occurred in frequencies below 0.13 Hz and was consistent with (1) residual large-scale magneto-mechanical effects correlated with slow variations in respiration volume and cardiac rhythm over time, and (2) local scale (<1 cm) effects localized in gray matter and vasculature most likely due to vascular dephasing mediated by a BOLD susceptibility change. While BOLD-related magnitude noise exhibited a TE dependence similar to BOLD, the 'BOLD-related' noise in the phase data increased with increasing TE and thus caused the overall phase noise to increase at a faster rate with TE than predicted by 1/TSNR. Interestingly, the spatial specificity of this effect was more evident for the higher resolution phase data, as opposed to the magnitude data, suggesting that at a higher spatial resolution the phase signal may contain more information on physiological processes than the magnitude signal.

Exposure to alternating electromagnetic fields and effects on the visual and visuomotor systems

Acute effects on the visual and visuo-motor systems by exposure to electromagnetic fields (EMFs) at a frequency and amplitude similar to those produced by MR imaging gradient coils were assessed. 40 volunteers were exposed in random order to three, time varying, magnetic field gradients (0, 20 and 10 mT m(-1)r.m.s.). The waveform was 50 cycles of a 490 Hz sinusoidal waveform repeated every second with a total duration of 10 min for each trial. The EMFs were generated using an in-house designed and built magnetic gradient coil and waveform generator. During each trial, a test battery assessing the visual sensory (FACT) and visuo-motor (Pursuit Aiming II and visual tracking) neurobehavioral domains was completed by all volunteers. The sequence of these tests was assigned at random for each volunteer. Performance in these tests was analysed using linear mixed effects models adjusted for confounding factors collected in a pre-trial questionnaire. Variability of the estimates was assessed using a delete-1 jack-knife procedure. There was a trend for visuo-motor accuracy to be reduced (p = 0.06) by 1% during high exposure, but not at medium exposure. There was a weaker trend for visual contrast sensitivity to be improved by 12% and 21% during medium and high exposure, respectively, compared with the non-exposed sessions (p = 0.08). These effects did not reach 5% statistical significance within a population of 40 volunteers, but also the magnitude of these effects did not depend on single "extreme" observations.

Cognitive effects of head-movements in stray fields generated by a 7 Tesla whole-body MRI magnet

The study investigates the impact of exposure to the stray magnetic field of a whole-body 7 T MRI scanner on neurobehavioral performance and cognition. Twenty seven volunteers completed four sessions, which exposed them to approximately 1600 mT (twice), 800 mT and negligible static field exposure. The order of exposure was assigned at random and was masked by placing volunteers in a tent to hide their position relative to the magnet bore. Volunteers completed a test battery assessing auditory working memory, eye-hand co-ordination, and visual perception. During three sessions the volunteers were instructed to complete a series of standardized head movements to generate additional time-varying fields ( approximately 300 and approximately 150 mT.s(-1) r.m.s.). In one session, volunteers were instructed to keep their heads as stable as possible. Performance on a visual tracking task was negatively influenced (P<.01) by 1.3% per 100 mT exposure. Furthermore, there was a trend for performance on two cognitive-motor tests to be decreased (P<.10). No effects were observed on working memory. Taken together with results of earlier studies, these results suggest that there are effects on visual perception and hand-eye co-ordination, but these are weak and variable between studies. The magnitude of these effects may depend on the magnitude of time-varying fields and not so much on the static field. While this study did not include exposure above 1.6 T, it suggests that use of strong magnetic fields is not a significant confounder in fMRI studies of cognitive function. Future work should further assess whether ultra-high field may impair performance of employees working in the vicinity of these magnets.