Dynamics of electron-phonon scattering: crystal- and angular-momentum transfer probed by resonant inelastic x-ray scattering

Experimentally, we observe angular-momentum transfer in electron-phonon scattering, although it is commonly agreed that phonons transfer mostly linear momentum. Therefore, the incorporation of angular momentum to describe phonons is necessary already for simple semiconductors and bears significant implications for the formation of new quasiparticles in correlated functional materials. Separation of linear and angular-momentum transfer in electron-phonon scattering is achieved by highly selective excitations on the femtosecond time scale of resonant inelastic x-ray scattering.

Spin-orbit mediated interference in the radiative and nonradiative channels of the La 4d core resonances

Symmetrical fluorescence yield profiles and asymmetrical electron yield profiles of the preresonances at the La N_{IV,V} x-ray absorption edge are experimentally observed in LaPO_{4} nanoparticles. Theoretical studies show that they are caused by interference effects. The spin-orbit interaction and the giant resonance produce symmetry entangled intermediate states that activate coherent scattering and alter the spectral distribution of the oscillator strength. The scattering amplitudes of the electron and fluorescence decays are further modified by the spin-orbit coupling in the final 5p;{5}epsilonl and 5p;{5}4f;{1} states.

Imaging short- and long-term training success in chronic aphasia

Background

To date, functional imaging studies of treatment-induced recovery from chronic aphasia only assessed short-term treatment effects after intensive language training. In the present study, we show with functional magnetic resonance imaging (fMRI), that different brain regions may be involved in immediate versus long-term success of intensive language training in chronic post-stroke aphasia patients.

Results

Eight patients were trained daily for three hours over a period of two weeks in naming of concrete objects. Prior to, immediately after, and eight months after training, patients overtly named trained and untrained objects during event-related fMRI. On average the patients improved from zero (at baseline) to 64.4% correct naming responses immediately after training, and treatment success remained highly stable at follow-up. Regression analyses showed that the degree of short-term treatment success was predicted by increased activity (compared to the pretraining scan) bilaterally in the hippocampal formation, the right precuneus and cingulate gyrus, and bilaterally in the fusiform gyri. A different picture emerged for long-term training success, which was best predicted by activity increases in the right-sided Wernicke's homologue and to a lesser degree in perilesional temporal areas.

Conclusion

The results show for the first time that treatment-induced language recovery in the chronic stage after stroke is a dynamic process. Initially, brain regions involved in memory encoding, attention, and multimodal integration mediated treatment success. In contrast, long-term treatment success was predicted mainly by activity increases in the so-called 'classical' language regions. The results suggest that besides perilesional and homologue language-associated regions, functional integrity of domain-unspecific memory structures may be a prerequisite for successful (intensive) language interventions.

Excessive Daytime Sleepiness Is a Common Symptom in Fabry Disease

Fabry disease (FD) is an X-linked lysosomal storage disorder characterized by a deficient activity of the enzyme α-galactosidase A, resulting in a vasculopathic involvement of various organ systems, e.g. cerebral structures. Marked cerebral vasculopathy with subsequent white matter lesions (WML) are a frequent finding in FD patients. Recent studies discussed an association between cerebral white matter changes and sleep-related disturbances of breathing, which may lead to excessive daytime sleepiness (EDS). A 56-year-old Caucasian female FD patient with EDS was admitted to our sleep laboratory. Overnight polysomnography showed a Cheyne-Stokes respiration pattern with significant O(2) desaturation. MR imaging revealed confluent WML including the brain stem, but no renal or cardiac involvement. We then evaluated the clinical data of 49 genetically proven FD patients (27 males; mean age 43 years) from our FD centre. With a frequency of 68%, EDS exceeds the prevalence of other common symptoms of FD (angiokeratomas 61%; acroparaesthesia 51%; renal involvement 29%; cardiac involvement 27%), and the prevalence of chronic fatigue (48%). EDS was independently associated with the physical component summary of the SF-36 data (corrected R(2) = -0.323, p < 0.001). EDS and age explained a quarter of variance in mental component summary (corrected R(2) = -0.253, p < 0.001). We conclude that EDS is a common and underdiagnosed symptom in FD patients, accompanied by a significant impact on quality of life. EDS might be caused by central breathing disorders due to an affection of brain regions associated with respiratory control in FD.

Kondo-cluster-glass state near a ferromagnetic quantum phase transition

We report on a comprehensive study of CePd(1-x)Rh(x) (0.6 <or= x <or= 0.95) poly- and single crystals close to the ferromagnetic instability by means of low-temperature ac susceptibility, magnetization, and volume thermal expansion. The signature of ferromagnetism in this heavy-fermion system can be traced from 6.6 K in CePd down to 25 mK for x = 0.87. Despite pronounced non-Fermi-liquid effects in both specific heat and thermal expansion, the Grüneisen ratio does not diverge as T --> 0, providing evidence for the absence of a quantum critical point. Instead, a peculiar "Kondo-cluster-glass" state is found for x >or= 0.65, and the non-Fermi-liquid effects in the specific heat, ac susceptibility, and magnetization are compatible with the quantum Griffiths phase scenario.

New non-magnetically ordered heavy-fermion system CeTiGe

Investigations of the susceptibility, electrical resistivity, specific heat and thermopower of CeTiGe at low temperatures show that this compound is a Kondo lattice system with an enhanced Sommerfeld coefficient γ≈0.3 J K(-2) mol(-1) and where the whole J = 5/2 multiplet is involved in the formation of the ground state. No magnetic order was observed down to 0.4 K. In the temperature range below 10 K we observed Fermi-liquid behavior as indicated by a ρ(T)∼T(2) dependence in the electrical resistivity and a linear specific heat and thermopower. Because of these results we classify CeTiGe as a moderate heavy-fermion system with a non-magnetic ground state.

Structural correlates of functional language dominance: a voxel-based morphometry study

BACKGROUND AND PURPOSE

The goal of this study was to explore the structural correlates of functional language dominance by directly comparing the brain morphology of healthy subjects with left- and right-hemisphere language dominance.

METHODS

Twenty participants were selected based on their language dominance from a cohort of subjects with known language lateralization. Structural differences between both groups were assessed by voxel-based morphometry, a technique that automatically identifies differences in the local gray matter volume between groups using high-resolution T1-weighted magnetic resonance images.

RESULTS

The main findings can be summarized as follows: (1) Subjects with right-hemisphere language dominance had significantly larger gray matter volume in the right hippocampus than subjects with left-hemisphere language dominance. (2) Leftward structural asymmetries in the posterior superior temporal cortex, including the planum temporale (PT), were observed in both groups.

CONCLUSIONS

Our study does not support the still prevalent view that asymmetries of the PT are related in a direct way to functional language lateralization. The structural differences found in the hippocampus underline the importance of the medial temporal lobe in the neural language network. They are discussed in the context of recent findings attributing a critical role of the hippocampus in the development of language lateralization.

Pattern and progression of white-matter changes in a case of posterior cortical atrophy using diffusion tensor imaging

BACKGROUND

The progression of white-matter changes in a case of posterior cortical atrophy (PCA) was examined over a period of 15 months using diffusion tensor imaging (DTI) and the association with neuropsychological variables was studied.

PATIENT AND METHODS

A PCA patient was observed over a period of 15 months. DTI and volumetric magnetic resonance imaging were obtained at visit 1 and 15 months later. Fractional anisotropy (FA) and volumetric changes were compared with findings in a typical case of Alzheimer disease (AD) and in 65 healthy volunteers, and the association of neuropsychological deficits with these changes was studied.

RESULTS

Reduction in FA was focused on the occipital lobe in the early stages of PCA. During the 15-month period, the FA values of the PCA patient tended to align with the FA ratios of the AD patient, with a more pronounced FA reduction in the parietal lobes, as opposed to a stable FA level in the occipital lobe. In addition to the DTI changes, clinical and neuropsychological symptoms deteriorated further. Brain volumes (grey matter, white matter and total normalised brain volume) of the PCA patient were substantially decreased compared with the control group, but loss of tissue volumes showed only marginal progression between visit 1 and 2.

CONCLUSIONS

The findings suggest that PCA starts as distinct clinical syndrome but in its later course might turn into a final pathway shared with AD. DTI might be helpful in detecting changes in cerebral white matter during disease progression in PCA patients.

Anterior cingulate reflects susceptibility to framing during attractiveness evaluation

Human cognitive decisions can be strongly susceptible to the manner in which options are presented ('framing effect'). Here we investigated the neural basis of response adjustments induced by changing frames during intuitive decisions. Evidence exists that the anterior cingulate cortex plays a general role in behavioral adjustments. We hypothesized, therefore, that the anterior cingulate cortex is also involved in the 'framing effect'. Our hypothesis was tested by using a binary attractiveness judgment task ('liking' versus 'nonliking') during functional magnetic resonance imaging. We found that the framing-related anterior cingulate cortex activity predicted how strongly susceptible an individual was to a biased response. Our results support the hypothesis that paralimbic processes are crucial for predicting an individual's susceptibility to framing.

Diffusion-Tensor Imaging at 3 T

OBJECTIVE

Fractional anisotropy (FA) is a powerful measure to study the integrity of the cerebral white matter in vivo. However, because clinical FA assessments are frequently based on single slice evaluations, intra- and interindividual comparisons are highly dependent on image alignment. We attempted to develop an observer-independent, fully automated technique for quantitative FA assessment.

MATERIALS AND METHODS

We employed whole brain diffusion tensor imaging at 3 T with an echo planar imaging sequence (isotropic spatial resolution 1.8 mm) on 4 patients (2x Alzheimer disease, 1x microangiopathy, 1x paraneoplastic disease) and 2 normal control groups (group "young," age 19-32 years; group "old," age 59-69 years). The images were spatially normalized to the standard brain template of the Montreal Neurologic Institute. We introduced a fractional anisotropy index (FAI) as a single measure for the mean tissue anisotropy in certain brain regions of interest. The regions of interest were defined by masks in relation to the Montreal Neurologic Institute coordinate space. We varied the spatial extent of the masks. Confidence intervals of the FAIs for both control groups were calculated.

RESULTS

We found the resulting FAIs to be highly robust against considerable mask variations (product-moment correlation: r > 0.97). The FAIs of the 4 patients presented with neurologic conditions associated with white matter alterations significantly fell outside the confidence intervals for normal FA.

CONCLUSION

FAIs based on mean fractional anisotropy values obtained from isotropic whole-head high-field diffusion tensor imaging by fully automated algorithms represent a robust and observer-independent measure for the comparative assessment of white matter integrity, ideally suited for further statistical treatments.

The association between scalp hair-whorl direction, handedness and hemispheric language dominance: is there a common genetic basis of lateralization?

The hemispheres of the human brain are functionally asymmetric. The left hemisphere tends to be dominant for language and superior in the control of manual dexterity. The mechanisms underlying these asymmetries are not known. Genetic as well as environmental factors are discussed. Recently, atypical anticlockwise hair-whorl direction has been related to an increased probability for non-right-handedness and atypical hemispheric language dominance. These findings are fascinating and important since hair-whorl direction is a structural marker of lateralization and could provide a readily observable anatomical clue to functional brain lateralization. Based on data on handedness and hair-whorl direction, Amar Klar proposed a genetic model ("random-recessive model") in that a single gene with two alleles controls both handedness and hair-whorl orientation (Klar, A.J.S., 2003. Human handedness and scalp hair-whorl direction develop from a common genetic mechanism. Genetics 165, 269-276). The present study was designed to further investigate the relationship between scalp hair-whorl direction with handedness and hemispheric language dominance. 1212 subjects were investigated for scalp hair-whorl direction and handedness. Additionally, we determined hemispheric language dominance (as assessed by a word generation task) in a subgroup of 212 subjects using functional transcranial Doppler sonography (fTCD). As for the single attributes - hair-whorl direction, handedness, and language dominance - we reproduced previously published results. However, we found no association between hair-whorl direction and either language dominance or handedness. These results strongly argue against a common genetic basis of handedness or language lateralization with scalp hair-whorl direction. Inspection of hair patterns will not help us to determine language dominance.

A new technique to evaluate the ability of cryoprotectors to prevent premature acrosome reaction in human spermatozoa

Acrosome reaction (AR) induced by low temperature has been used to evaluate sperm function; it correlates adequately with the fertilization percentages in vitro. In this study, the technique of AR induction by low temperature was used to evaluate the effect in the protection of the acrosome by cryopreservatives normally used in human semen cryopreservation. Donor sperm selected by use of the migration sedimentation technique was incubated in human tubal fluid medium, added to dimethyl sulphoxide 1 m, ethylene glycol 0.75 m, glycerol 1 m, incubated at 4 degrees C and 20 degrees C (as a control) for 18 h, and then for 3 h at 37 degrees C in a cell incubator. The AR was evaluated by triple stain in 100 viable spermatozoa. The effect of cryopreservatives on acrosome preservation in samples incubated for 18 h at 4 degrees C was as follows: 78% intact acrosome for glycerol, 77.8% intact acrosome for dimethyl sulphoxide and 96.2% intact acrosome for ethylene glycol (P < 0.0025 compared with glycerol and dimethyl-sulphoxide). The sperm samples incubated with cryopreservatives for 18 h at 20 degrees C did not show an increase in the percentage of AR in samples incubated with glycerol and ethylene glycol, while a significant variation was observed in the sample incubated with dimethyl sulphoxide (P < 0.001). Additional incubation for 3 h at 37 degrees C significantly increased the AR only in the sample incubated with glycerol (P < 0.001). Acrosome preservation is essential in the fertilization process and the evaluation of acrosome reaction induction by low temperature test was satisfactory. This test proves that ethylene glycol presents a greater protective effect on the acrosome preservation of human spermatozoa.

Non-Fermi liquid states in the pressurized CeCu2(Si1-xGex)2 system: two critical points

In the archetypal strongly correlated electron superconductor CeCu2Si2 and its Ge-substituted alloys CeCu2(Si1-xGex)2 two quantum phase transitions--one magnetic and one of so far unknown origin-can be crossed as a function of pressure. We examine the associated anomalous normal state by detailed measurements of the low temperature resistivity (rho) power-law exponent alpha. At the lower critical point (at pcl, 1<or=alpha<or=1.5) alpha depends strongly on Ge concentration x and thereby on disorder level, consistent with a Hlubina-Rice-Rosch scenario of critical scattering off antiferromagnetic fluctuations. By contrast, alpha is independent of x at the upper quantum phase transition (at pc2, alpha approximately equal to 1), suggesting critical scattering from local or q=0 modes, in agreement with a density- or valence-fluctuation approach.

Transcranial magnetic stimulation—a sandwich coil design for a better sham

OBJECTIVE

To improve the quality of TMS studies by developing a new sham condition.

METHODS

We describe a novel and easily arranged TMS set-up of two standard TMS coils and a magnetic shield, stacked like a sandwich. In a first step we compare the magnetic field in the sham and verum conditions. In a second step we ask six subjects to rate the stimulation intensity.

RESULTS

The magnetic field in the sham mode is reduced to about one eighth of that during verum stimulation. The attenuation of the magnetic field is not limited to the actual stimulation site but also effective at neighbouring brain areas, avoiding direct and indirect stimulation via connected neural pathways. This also minimizes stimulation of the skin, but as a consequence allows subjects to distinguish between verum and sham conditions when these are contrasted directly. The position of the coil system and the acoustic sensations are indistinguishable between sham and verum condition. Subjects are not able to discriminate TMS position and condition by external cues.

CONCLUSIONS

The proposed TMS setup is simple and allows verum and sham TMS without interaction of the researcher. If used with the magnetic shield, the magnetic field in the brain is attenuated most.

SIGNIFICANCE

With the sandwich TMS coil system it is possible to improve the quality of TMS studies.

Evidence for a neural correlate of a framing effect: Bias-specific activity in the ventromedial prefrontal cortex during credibility judgments

BACKGROUND

Neural processes within the medial prefrontal cortex play a crucial role in assessing and integrating emotional and other implicit information during decision-making. Phylogenetically, it was important for the individual to assess the relevance of all kinds of environmental stimuli in order to adapt behavior in a flexible manner. Consequently, we can in principle not exclude that environmental information covertly influences the evaluation of actually decision relevant facts ("framing effect").

OBJECTIVE

To test the hypothesis that the medial prefrontal cortex is involved into a framing effect we employed functional magnetic resonance imaging (fMRI) during a binary credibility judgment task.

METHODS

Twenty-one subjects were asked to judge 30 normalized news magazine headlines by forced answers as "true" or "false". To confound the judgments by formally irrelevant framing information we presented each of the headlines in four different news magazines characterized by varying credibility. For each subject the susceptibility to the judgment confounder (framing information) was assessed by magazine-specific modifications of the answers given.

RESULTS

We could show that individual activity changes of the ventromedial prefrontal cortex during the judgments correlate with the degree of an individual's susceptibility to the framing information.

CONCLUSION

We found (i) a neural correlate of a framing effect as postulated by behavioral decision theorists that (ii) reflects interindividual differences in the degree of the susceptibility to framing information.

Scalp position and efficacy of transcranial magnetic stimulation

OBJECTIVE

To assess the impact of the scalp site on the biological effects of TMS.

METHODS

We performed high-resolution, three-dimensional whole head magnetic resonance imaging (MRI) in a healthy subject, systematically measured the scalp-to-cortex distance across the head and calculated the resulting electric field in the superficial cortex.

RESULTS

The variability in scalp-to-cortex distance led to differences in calculated cortical electric field strengths of a factor of two. A major portion of this variability was explained by a lateral to medial gradient with scalp-to-cortex distances being greatest close to the midline and smallest towards the temporal coordinates.

CONCLUSIONS

Because of the medio-lateral gradient in scalp-to-cortex distance interventions tailored on the basis of effects of TMS in the motor system will systematically induce stronger than expected electric currents when performed laterally to the motor spot.

SIGNIFICANCE

The biological effects of TMS outside the motor spot may be markedly different from those observed in the motor system and this should be taken into account to optimize TMS for the evaluation or treatment of neuropsychiatric disorders.

Atypical hemispheric dominance for attention: functional MRI topography

The right hemisphere is predominantly involved in tasks associated with spatial attention. However, left hemispheric dominance for spatial attention can be found in healthy individuals, and both spatial attention and language can be lateralized to the same hemisphere. Little is known about the underlying regional distribution of neural activation in these 'atypical' individuals. Previously a large number of healthy subjects were screened for hemispheric dominance of visuospatial attention and language, using functional Doppler ultrasonography. From this group, subjects were chosen who were 'atypical' for hemispheric dominance of visuospatial attention and language, and their pattern of brain activation was studied with functional magnetic resonance imaging during a task probing spatial attention. Right-handed subjects with the 'typical' pattern of brain organization served as control subjects. It was found that subjects with an inverted lateralization of language and spatial attention (language right, attention left) recruited left-hemispheric areas in the attention task, homotopic to those recruited by control subjects in the right hemisphere. Subjects with lateralization of both language and attention to the right hemisphere activated an attentional network in the right hemisphere that was comparable to control subjects. The present findings suggest that not the hemispheric side, but the intrahemispheric pattern of activation is the distinct feature for the neural processes underlying language and attention.

Nonlinear responses within the medial prefrontal cortex reveal when specific implicit information influences economic decision making

BACKGROUND AND PURPOSE

The authors used functional magnetic resonance imaging (fMRI) to investigate how individual economic decisions are influenced by implicit memory contributions.

METHODS

Twenty-two participants were asked to make binary decisions between different brands of sensorily nearly undistinguishable consumer goods. Changes of brain activity comparing decisions in the presence or absence of a specific target brand were detected by fMRI.

RESULTS

Only when the tar get brand was the participant's favorite one did the authors find reduced activation in the dorsolateral prefrontal, posterior parietal, and occipital cortices and the left premotor area (Brodmann areas [BA] 9, 46, 7/19, and 6). Simultaneously, activity was increased in the inferior precuneus and posterior cingulate (BA 7), right superior frontal gyrus (BA 10), right supramarginal gyrus (BA 40), and, most pronounced, in the ventromedial prefrontal cortex (BA 10).

CONCLUSIONS

For products mainly distinguishable by brand information, the authors revealed a nonlinear winner-take-all effect for a participant's favorite brand characterized, on one hand, by reduced activation in brain areas associated with working memory and reasoning and, on the other hand, increased activation in areas involved in processing of emotions and self-reflections during decision making.

Crossed cerebro-cerebellar language dominance

In addition to its traditional role in motor control, the cerebellum has been implicated in various cognitive and linguistic functions. Lesion, anatomic, and functional imaging studies indicate a link between left frontal language regions and the right cerebellum. To probe the specificity of this circuit, we examined the association between language-related lateralized activation of the frontal cortex with lateralized activation of the cerebellum. Functional magnetic resonance imaging (fMRI) was carried out during letter-cued word generation in 14 healthy subjects: 7 subjects displayed typical left-hemisphere and 7 subjects displayed atypical right-hemisphere language dominance. We found activation of the cerebellar hemisphere contralateral to the language-dominant cerebral hemisphere in each subject. The cerebellar activation was confined to the lateral posterior cerebellar hemisphere (lobule VI, VII B, Cr I, Cr II). This study demonstrates that crossed cerebral and cerebellar language dominance is a typical characteristic of brain organization. The functional significance of the reported activations can now be tested in patients with lesions of the lateral posterior cerebellum.

Hippocampus activity differentiates good from poor learners of a novel lexicon

Language proficiency is a key to academic and workplace success for native and non-native speakers. It is largely unknown, however, why some people pick up languages more easily than others. We used event-related functional magnetic resonance imaging (e-fMRI) to elucidate which brain regions are modulated during the acquisition of a novel lexicon and which of these learning-related activity changes correlated with general semantic language knowledge. Fourteen healthy young subjects learned a novel vocabulary of 45 concrete nouns via an associative learning principle over the course of five blocks during e-fMRI. As a control condition, subjects took part in a structurally identical "No-Learning" condition lacking any learning principle. Overall, increasing vocabulary proficiency was associated with (intercorrelated) modulations of activity within the left hippocampus and the left fusiform gyrus, regions involved in the binding and integration of multimodal stimuli, and with an increasing activation of the left inferior parietal cortex, the presumed neural store of phonological associations. None of these activity changes were observed during the control condition. Furthermore, subjects who showed less suppression of hippocampal activity over learning blocks scored higher on semantic knowledge in their native language and learned the novel vocabulary more efficiently. Our findings indicate that (a) the successful acquisition of a new lexicon depends on correlated amplitude changes between the left hippocampus and neocortical regions and (b) learning-related hippocampus activity is a stable marker of individual differences in the ability to acquire and master vocabularies.