EEG Microstates in Social and Affective Neuroscience.

Social interactions require both the rapid processing of multifaceted socio-affective signals (e.g., eye gaze, facial expressions, gestures) and their integration with evaluations, social knowledge, and expectations. Researchers interested in understanding complex social cognition and behavior face a "black box" problem: What are the underlying mental processes rapidly occurring between perception and action and why are there such vast individual differences? In this review, we promote electroencephalography (EEG) microstates as a powerful tool for both examining socio-affective states (e.g., processing whether someone is in need in a given situation) and identifying the sources of heterogeneity in socio-affective traits (e.g., general willingness to help others). EEG microstates are identified by analyzing scalp field maps (i.e., the distribution of the electrical field on the scalp) over time. This data-driven, reference-independent approach allows for identifying, timing, sequencing, and quantifying the activation of large-scale brain networks relevant to our socio-affective mind. In light of these benefits, EEG microstates should become an indispensable part of the methodological toolkit of laboratories working in the field of social and affective neuroscience.

Alpha-2 Adrenoreceptor Antagonist Yohimbine Potentiates Consolidation of Conditioned Fear.

BACKGROUND: Hyperconsolidation of aversive associations and poor extinction learning have been hypothesized to be crucial in the acquisition of pathological fear. Previous animal and human research points to the potential role of the catecholaminergic system, particularly noradrenaline and dopamine, in acquiring emotional memories. Here, we investigated in a between-participants design with 3 groups whether the noradrenergic alpha-2 adrenoreceptor antagonist yohimbine and the dopaminergic D2-receptor antagonist sulpiride modulate long-term fear conditioning and extinction in humans. METHODS: Fifty-five healthy male students were recruited. The final sample consisted of n = 51 participants who were explicitly aware of the contingencies between conditioned stimuli (CS) and unconditioned stimuli after fear acquisition. The participants were then randomly assigned to 1 of the 3 groups and received either yohimbine (10 mg, n = 17), sulpiride (200 mg, n = 16), or placebo (n = 18) between fear acquisition and extinction. Recall of conditioned (non-extinguished CS+ vs CS-) and extinguished fear (extinguished CS+ vs CS-) was assessed 1 day later, and a 64-channel electroencephalogram was recorded. RESULTS: The yohimbine group showed increased salivary alpha-amylase activity, confirming a successful manipulation of central noradrenergic release. Elevated fear-conditioned bradycardia and larger differential amplitudes of the N170 and late positive potential components in the event-related brain potential indicated that yohimbine treatment (compared with a placebo and sulpiride) enhanced fear recall during day 2. CONCLUSIONS: These results suggest that yohimbine potentiates cardiac and central electrophysiological signatures of fear memory consolidation. They thereby elucidate the key role of noradrenaline in strengthening the consolidation of conditioned fear associations, which may be a key mechanism in the etiology of fear-related disorders.

Learning dynamics of electrophysiological brain signals during human fear conditioning.

Electrophysiological studies in rodents allow recording neural activity during threats with high temporal and spatial precision. Although fMRI has helped translate insights about the anatomy of underlying brain circuits to humans, the temporal dynamics of neural fear processes remain opaque and require EEG. To date, studies on electrophysiological brain signals in humans have helped to elucidate underlying perceptual and attentional processes, but have widely ignored how fear memory traces evolve over time. The low signal-to-noise ratio of EEG demands aggregations across high numbers of trials, which will wash out transient neurobiological processes that are induced by learning and prone to habituation. Here, our goal was to unravel the plasticity and temporal emergence of EEG responses during fear conditioning. To this end, we developed a new sequential-set fear conditioning paradigm that comprises three successive acquisition and extinction phases, each with a novel CS+/CS- set. Each set consists of two different neutral faces on different background colors which serve as CS+ and CS-, respectively. Thereby, this design provides sufficient trials for EEG analyses while tripling the relative amount of trials that tap into more transient neurobiological processes. Consistent with prior studies on ERP components, data-driven topographic EEG analyses revealed that ERP amplitudes were potentiated during time periods from 33-60 ms, 108-200 ms, and 468-820 ms indicating that fear conditioning prioritizes early sensory processing in the brain, but also facilitates neural responding during later attentional and evaluative stages. Importantly, averaging across the three CS+/CS- sets allowed us to probe the temporal evolution of neural processes: Responses during each of the three time windows gradually increased from early to late fear conditioning, while long-latency (460-730 ms) electrocortical responses diminished throughout fear extinction. Our novel paradigm demonstrates how short-, mid-, and long-latency EEG responses change during fear conditioning and extinction, findings that enlighten the learning curve of neurophysiological responses to threat in humans.

Force chains in crystalline and frustrated packing visualized by stress-birefringent spheres.

Force networks play an important role in the stability of configurations when granular material is packed into a container. These networks can redirect part of the weight of grains inside a container to the side walls. We employ monodisperse stress-birefringent spheres to visualize the contact forces in a quasi-2D and a nearly-2D configuration of these spheres in a thin cuboid cell. The packing structures are particularly simple: a hexagonal lattice in the ground state when the cell width is equal to the sphere diameter, and a frustrated, slightly distorted lattice in thicker cells. The force redistribution is substantially changed by this geometrical modification. In both cases, we observe an 'inverse' Janssen effect with the pressure decreasing from the top to the bottom of the container when the material is loaded with a weight on top of the vessel.

Dynamic light scattering from single macroscopic particles.

Here we present a methodology to characterize the light intensity fluctuations that arise from rotations of individual granular particles. We describe a setup for dynamic light scattering measurements on individual macroscopic particles and isolate the contribution from rotations of the individual particles to the obtained correlation functions. The results show that rotation of granular particles results in a significant contribution to scattered light intensity fluctuations, a phenomenon not considered so far in dynamic light scattering measurements on fluidized granular media. The results presented here may thus form the basis for an extended light scattering methodology for granular media, and improve the selection of granular particles according to their dynamic light scattering signal.

Velocity Distribution of a Homogeneously Cooling Granular Gas.

In contrast to molecular gases, granular gases are characterized by inelastic collisions and require therefore permanent driving to maintain a constant kinetic energy. The kinetic theory of granular gases describes how the average velocity of the particles decreases after the driving is shut off. Moreover, it predicts that the rescaled particle velocity distribution will approach a stationary state with overpopulated high-velocity tails as compared to the Maxwell-Boltzmann distribution. While this fundamental theoretical result was reproduced by numerical simulations, an experimental confirmation is still missing. Using a microgravity experiment that allows the spatially homogeneous excitation of spheres via magnetic fields, we confirm the theoretically predicted exponential decay of the tails of the velocity distribution.

Additional Transition Line in Jammed Asymmetric Bidisperse Granular Packings.

We present numerical evidence for an additional discontinuous transition, upon compression, inside the jammed regime for an asymmetric bidisperse granular packing. This additional transition line separates jammed states with networks of predominantly large particles from jammed networks formed by both large and small particles, and the transition is indicated by a discontinuity in the number of particles contributing to the jammed network. The additional transition line emerges from the curves of jamming transitions and terminates in an end point where the discontinuity vanishes. The additional line is starting at a size ratio around δ=0.22 and grows longer for smaller δ. For δ→0, the additional transition line approaches a limit that can be derived analytically. The observed jamming scenarios are reminiscent of glass-glass transitions found in colloidal glasses.

Fear Extinction Recall Modulates Human Frontomedial Theta and Amygdala Activity.

Human functional magnetic resonance imaging (fMRI) and electroencephalography (EEG) studies, as well as animal studies, indicate that the amygdala and frontomedial brain regions are critically involved in conditioned fear and that frontomedial oscillations in the theta range (4-8 Hz) may support communication between these brain regions. However, few studies have used a multimodal approach to probe interactions among these key regions in humans. Here, our goal was to bridge the gap between prior human fMRI, EEG, and animal findings. Using simultaneous EEG-fMRI recordings 24 h after fear conditioning and extinction, conditioned stimuli presented (CS+E, CS-E) and not presented during extinction (CS+N, CS-N) were compared to identify effects specific to extinction versus fear recall. Differential (CS+ vs. CS-) electrodermal, frontomedial theta (EEG) and amygdala responses (fMRI) were reduced for extinguished versus nonextinguished stimuli. Importantly, effects on theta power covaried with effects on amygdala activation. Fear and extinction recall as indicated by theta explained 60% of the variance for the analogous effect in the right amygdala. Our findings show for the first time the interplay of amygdala and frontomedial theta activity during fear and extinction recall in humans and provide insight into neural circuits consistently linked with top-down amygdala modulation in rodents.

Persistent Anti-Correlations in Brownian Dynamics Simulations of Dense Colloidal Suspensions Revealed by Noise Suppression.

Transport properties of a hard-sphere colloidal fluid are investigated by Brownian dynamics simulations. We implement a novel algorithm for the time-dependent velocity-autocorrelation function (VACF) essentially eliminating the noise of the bare random motion. The measured VACF reveals persistent anti-correlations manifested by a negative algebraic power-law tail t^{-5/2} at all densities. At small packing fractions the simulations fully agree with the analytic low-density prediction, yet the amplitude of the tail becomes dramatically suppressed as the packing fraction is increased. The mode-coupling theory of the glass transition provides a qualitative explanation for the strong variation in terms of the static compressibility as well as the slowing down of the structural relaxation.

Aversive Imagery Causes De Novo Fear Conditioning.

In classical fear conditioning, neutral conditioned stimuli that have been paired with aversive physical unconditioned stimuli eventually trigger fear responses. Here, we tested whether aversive mental images systematically paired with a conditioned stimulus also cause de novo fear learning in the absence of any external aversive stimulation. In two experiments (N = 45 and N = 41), participants were first trained to produce aversive, neutral, or no imagery in response to three different visual-imagery cues. In a subsequent imagery-based differential-conditioning paradigm, each of the three cues systematically coterminated with one of three different neutral faces. Although the face that was paired with the aversive-imagery cue was never paired with aversive external stimuli or threat-related instructions, participants rated it as more arousing, unpleasant, and threatening and displayed relative fear bradycardia and fear-potentiated startle. These results could be relevant for the development of fear and related disorders without trauma.

Granular ionic crystals in a small nutshell.

Ordered two-dimensional arrangements of triboelectrically oppositely charged granular particles have been reported several times, but observations of bulk ordered binary granular particle packings are singular. We attribute this suppression of triboelectrically induced order to the concurrent behaviour of granular particles to pack densest due to gravity. We show that triboelectrically induced order robustly emerges in a container that does not allow for crystallization into a dense packing under gravity. It turns out that the triboelectrically ordered structure follows Pauling's predictions for atomic ionic crystals in many aspects, but also exhibits systematic deviations. We discuss how the emergence of order in an incommensurate container, the deviations from Pauling's predictions and the gravitational potential energy of the particles are connected.

Distinguishing noisy crystalline structures using bond orientational order parameters.

The bond orientational order parameters originally introduced by Steinhardt et al. (Phys. Rev. B 28, 784 (1983)) are a common tool for local structure characterization in soft matter studies. Recently, Mickel et al. (J. Chem. Phys. 138, 044501 (2013)) highlighted problems of the bond orientational order parameters due to the ambiguity of the underlying neighbourhood definition. Here we show the difficulties to distinguish common structures like FCC- and BCC-based structures with the suggested neighbourhood definitions when noise is introduced. We propose a simple improvement to the neighbourhood definition that results in robust and continuous bond orientational order parameters with which we can accurately distinguish crystal structures even when noise is present.

Observational retrospective study on socio-economic and quality of life outcomes in 41 patients with adolescent idiopathic scoliosis 5 years after bracing combined with physiotherapeutic scoliosis-specific exercises (PSSE).

PURPOSE: We analysed socio-economic- and health-related quality of life (primary outcome) and radiological outcome (secondary outcome) 5 years after full time rigid bracing (FTRB) plus physiotherapeutic scoliosis-specific exercises (PSSE) in adolescent idiopathic scoliosis. METHODS: We included 41 patients (38 female and 3 male) treated with FTRB (Chênau brace) and PSSE (Schroth) between 2001 and 2010. The study protocol included a clinical and radiological examination, the completion of the SRS-24 questionnaire and acquisition of data on socio-economic factors (educational and employment status) and physical activity. Descriptive statistics were used to analyse the data; differences between patients with mild (< 30°) and severe curves (30°-50°) regarding hrQoL outcomes were analysed using the Mann-Whitney U Test. RESULTS: Primary outcomes showed full employment (higher education, 39%, and full-time work, 61%) and the majority of the patients (79.9%) performing moderate sports two to four times per week. The SRS-24 questionnaire produced a total mean score (MS) of 4.0 (79.9%). Patients with mild curves had a significantly better total score (MS 4.1 vs. MS 3.8, p = 0.020) and were more satisfied with the treatment (MS 4.3 vs MS 3.9, p = 0.020). As to the secondary outcomes, from start of bracing to follow-up (a mean of 6.7 years after brace weaning), the average Cobb angle changed from 28.6° to 25.6° (range 4°-48°); in 51.2% the curve angles could be maintained after weaning. CONCLUSIONS: Compared with the literature, our results showed similar curve development and hrQoL (pain, self-image and function) and better results regarding satisfaction with treatment. In comparison with the average population, there were no disadvantages as to occupation, education and sports. These slides can be retrieved under Electronic Supplementary Material.

Outcome following excision of the radial head in children with open physes for impaired elbow motion.

BACKGROUND: Only few reports have described the outcome of pediatric patients following radial head resection. Therefore, the aim of the present study was to assess clinical and radiologic outcome of patients with open physes following resection of the radial head. MATERIALS AND METHODS: Skeletally immature patients treated with resection of the radial head were included. Range of motion (ROM) of the elbow joint was compared with preoperative values. Grip strength, pronation and supination strength, and carrier angle were compared with the unaffected side. Radiographs were assessed for signs of arthrosis, radial migration, and perifocal ossification. Disabilities of the Arm, Shoulder and Hand and Mayo Elbow Performance scores were obtained. RESULTS: The study included 7 patients (mean age, 11 years), 5 with post-traumatic and 2 with congenitally impaired elbow joint motion. Mean follow-up was 47 months. Pronation/supination ROM improved significantly (P = .018). Extension/flexion ROM did not improve significantly (P = .122). Although grip strength (P = .027) and pronation strength (P = .028) of the affected side were significantly lower compared with the contralateral side, supination strength did not differ significantly (P = .176). The carrying angle was increased in 3 patients. Significant radial migration occurred (mean, 3 mm; standard deviation [SD], 3 mm; P = .018). Arthrosis was found in 3 patients. The mean Disabilities of the Arm, Shoulder and Hand score was 16.1 (range 8.8-30.8; SD, 10.1) and mean Mayo Elbow Performance Score was 88 (range, 70-100; SD, 12). CONCLUSIONS: Radial head excision may be considered for selected patients with open physes in cases of severe impairment of pronation/supination. However, sequelae such as radial migration, arthrosis, and elevation of the carrying angle should be expected.

Fearfulness, neuroticism/anxiety, and COMT Val158Met in long-term fear conditioning and extinction.

Individual differences in long-term stability of fear memories are of potential relevance for stable dispositions related to threat processing, such as neuroticism/anxiety and fearfulness. As previous research suggests a prominent role of dopamine for the retention of conditioned and extinguished fear, dopaminergic gene polymorphisms may also relate to individual differences in fear stability. While the COMT Val158Met polymorphism causes individual differences in prefrontal dopamine, its associations with human long-term fear extinction are currently unknown. Here, n = 30/29/28 healthy male Val/Val, Val/Met and Met/Met carriers, respectively, underwent a two-day differential conditioning paradigm with fear acquisition and extinction on Day 1 and a recall test on Day 2 with recordings of EEG and ECG. Fearfulness but not neuroticism/anxiety predicted fear bradycardia (i.e., heart period slowing) during Day 1 fear acquisition while it did not affect extinction or Day 2 fear recall. In contrast, COMT Val158Met significantly modulated Day 2 fear recall as evident in fear bradycardia and Late Positive Potential (LPP) amplitudes while it did not affect Day 1 fear or extinction learning. Furthermore, exploratory analyses revealed that individual differences in fear bradycardia during Day 2 extinction recall depended on Day 1 extinction success. Importantly, this contingency was (a) modulated by COMT Val158Met and (b) significantly reduced in high vs. low neuroticism/anxiety. The present study indicates that (a) individual differences in dopaminergic genotypes may affect the long-term stability of fear memories and (b) fearfulness vs. neuroticism/anxiety might play distinct roles in initial fear reactions vs. long-term stability of fear memories, respectively.

Rheology of Inelastic Hard Spheres at Finite Density and Shear Rate.

Considering a granular fluid of inelastic smooth hard spheres, we discuss the conditions delineating the rheological regimes comprising Newtonian, Bagnoldian, shear thinning, and shear thickening behavior. Developing a kinetic theory, valid at finite shear rates and densities around the glass transition density, we predict the viscosity and Bagnold coefficient at practically relevant values of the control parameters. The determination of full flow curves relating the shear stress σ to the shear rate γ[over ˙] and predictions of the yield stress complete our discussion of granular rheology derived from first principles.

Double origin of stochastic granular tribocharging.

The mechanisms underlying triboelectric charging have a stochastic nature. We investigate how this randomness affects the distributions of charges generated on granular particles during either a single or many collisions. The charge distributions we find in our experiments are more heavy-tailed than normal distributions with an exponential decay of the probability, they are asymmetric, and exhibit charges of both signs. Moreover, we find a linear correlation between the width and mean of these distributions. We rationalize these findings with a model for triboelectric charging which combines stochastic charge separation during contact and stochastic charge recombination after separation of the surfaces. Our results further imply that subsequent charging events are not statistically independent.

Medial patellofemoral ligament (MPFL) reconstruction in combination with a modified grammont technique leads to favorable mid-term results in adolescents with recurrent patellofemoral dislocations.

PURPOSE: The aim of the present study is to present the outcome of a cohort of adolescent patients with trochlear dysplasia and elevated tibial tuberosity trochlear groove (TTTG) distance suffering from recurrent patellar dislocation. Treatment consisted of medial patellofemoral ligament (MPFL) reconstruction and a modified Grammont procedure. METHODS: MRI examinations were obtained pre- and postoperatively. Trochlear dysplasia was classified according to Déjour, and TTTG was measured on MRI. The Tegner Activity Scale and the Kujala Knee Score were assessed preoperatively and at follow-up. The Kujala Knee score and the IKDC 2000 knee score were documented at follow-up (median 50, range 20-61 months; SD 16.6). RESULTS: Seven knees of six patients (median age 16.5 years, range 14-17 years) with trochlear dysplasia and elevated TTTG distance (median 17 mm, range 16.1-21.9 mm; SD 2.8) were treated. Trochlear dysplasia was classified as Déjour type A in 1, type B in 5, and type C in 1 knee. The Kujala Knee Score significantly increased from values of 55 (range 17-88; SD 25.9) to 94 (range 73-100; SD 9.1) at follow-up (p = 0.028). TAS improved from preoperative 2 (range 0-7; SD 2.5) to 5 (range 4-9; SD 1.8) at follow-up (p = 0.034). Median IKDC 2000 Knee Score at follow-up was 89 (range 61-100, SD 13.4). No re-dislocations were encountered. CONCLUSION: In selected adolescents with recurrent patellofemoral instability, MPFL reconstruction in combination with a modified Grammont technique yields excellent functional outcome and could, therefore, help to avoid major procedures, such as osteotomies. LEVEL OF EVIDENCE: Therapeutic, Level IV.

Spatial Distributions of Local Elastic Moduli Near the Jamming Transition.

Recent progress on studies of the nanoscale mechanical responses in disordered systems has highlighted a strong degree of heterogeneity in the elastic moduli. In this contribution, using computer simulations, we study the elastic heterogeneities in athermal amorphous solids--composed of isotropic static sphere packings--near the jamming transition. We employ techniques based on linear response methods that are amenable to experimentation. We find that the local elastic moduli are randomly distributed in space and are described by Gaussian probability distributions, thereby lacking any significant spatial correlations, that persist all the way down to the transition point. However, the shear modulus fluctuations grow as the jamming threshold is approached, which is characterized by a new power-law scaling. Through this diverging behavior we are able to identify a characteristic length scale, associated with shear modulus heterogeneities, that distinguishes between bulk and local elastic responses.

Multiple glass singularities and isodynamics in a core-softened model for glass-forming systems.

We investigate the slow dynamics of a simple glass former whose interaction potential is the sum of a hard core and a square shoulder repulsion. According to mode coupling theory, the competition between the two repulsive length scales gives rise to a complex dynamic scenario: besides the fluid-glass line, the theory predicts a glass-glass line in the temperature-packing fraction plane with two end points. Interestingly, for critical values of the square-shoulder parameters, such end points can be accessed from the liquid phase. We verify, via extensive numerical simulations, the existence of both points through the observation of an unconventional subdiffusive/logarithmic dynamical behavior. Unexpectedly, we also discover that the simultaneous presence of two end points generates special loci in the state diagram along which the dynamics is identical at all length and time scales.