Value encoding in the globus pallidus: fMRI reveals an interaction effect between reward and dopamine drive

The external part of the globus pallidus (GPe) is a core nucleus of the basal ganglia (BG) whose activity is disrupted under conditions of low dopamine release, as in Parkinson's disease. Current models assume decreased dopamine release in the dorsal striatum results in deactivation of dorsal GPe, which in turn affects motor expression via a regulatory effect on other nuclei of the BG. However, recent studies in healthy and pathological animal models have reported neural dynamics that do not match with this view of the GPe as a relay in the BG circuit. Thus, the computational role of the GPe in the BG is still to be determined. We previously proposed a neural model that revisits the functions of the nuclei of the BG, and this model predicts that GPe encodes values which are amplified under a condition of low striatal dopaminergic drive. To test this prediction, we used an fMRI paradigm involving a within-subject placebo-controlled design, using the dopamine antagonist risperidone, wherein healthy volunteers performed a motor selection and maintenance task under low and high reward conditions. ROI-based fMRI analysis revealed an interaction between reward and dopamine drive manipulations, with increased BOLD activity in GPe in a high compared to low reward condition, and under risperidone compared to placebo. These results confirm the core prediction of our computational model, and provide a new perspective on neural dynamics in the BG and their effects on motor selection and cognitive disorders

Grundlagen der computerassistierten Chirurgie

Zusammenfassung: Der Einsatz von Navigationssystemen in der orthopädischen Chirurgie und speziell in der Knieendoprothetik findet immer weitere Verbreitung. Dieser Beitrag stellt die grundlegenden technologischen Konzepte vor, auf denen moderne Computerassistenzsysteme beruhen, zeigt ihre Ausprägungen in den aktuell verwendeten Systemen auf und reißt verschiedene Entwicklungen an, die einen Einfluss auf zukünftige Produkte haben könnten. Prinzipiell lassen sich in jedem Navigationssystem 3 Komponenten identifizieren. Das therapeutische Objekt ist diejenige anatomische Struktur, die das Ziel der navigierten Operation darstellt. Das virtuelle Objekt ist ein Abbild des therapeutischen Objekts. Hier können radiologische oder vom Rechner generierte Darstellungen zu Einsatz kommen. Der Navigator schließlich dient zur Erfassung von Position und Lage von Instrumenten und Anatomie und stellt sicher, dass chirurgische Aktionen im Operationsfeld am Navigationsmonitor wiedergegeben werden könne

Soliton excitation in waveguide arrays with an effective intermediate dimensionality

We reveal and observe experimentally significant modifications undertaken by discrete solitons in waveguide lattices upon the continuous transformation of the lattice structure from one-dimensional to two-dimensional. Light evolution and soliton excitation in arrays with a gradually increasing number of rows are investigated, yielding solitons with an effective reduced dimensionality residing at the edge and in the bulk of the lattice.Comment: 14 pages, 5 figures, to appear in Physical Review Letter

Fermion Production in the Background of Minkowski Space Classical Solutions in Spontaneously Broken Gauge Theory

We investigate fermion production in the background of Minkowski space solutions to the equations of motion of $SU(2)$ gauge theory spontaneously broken via the Higgs mechanism. First, we attempt to evaluate the topological charge $Q$ of the solutions. We find that for solutions $Q$ is not well-defined as an integral over all space-time. Solutions can profitably be characterized by the (integer-valued) change in Higgs winding number $\Delta N_H$. We show that solutions which dissipate at early and late times and which have nonzero $\Delta N_H$ must have at least the sphaleron energy. We show that if we couple a quantized massive chiral fermion to a classical background given by a solution, the number of fermions produced is $\Delta N_H$, and is not related to $Q$.Comment: Version to be published. Argument showing that the topological charge of solutions is undefined has been strengthened and clarified. Conclusions unchange

Drosophila Adaptation to Viral Infection through Defensive Symbiont Evolution

Microbial symbionts can modulate host interactions with biotic and abiotic factors. Such interactions may affect the evolutionary trajectories of both host and symbiont. Wolbachia protects Drosophila melanogaster against several viral infections and the strength of the protection varies between variants of this endosymbiont. Since Wolbachia is maternally transmitted, its fitness depends on the fitness of its host. Therefore, Wolbachia populations may be under selection when Drosophila is subjected to viral infection. Here we show that in D. melanogaster populations selected for increased survival upon infection with Drosophila C virus there is a strong selection coefficient for specific Wolbachia variants, leading to their fixation. Flies carrying these selected Wolbachia variants have higher survival and fertility upon viral infection when compared to flies with the other variants. These findings demonstrate how the interaction of a host with pathogens shapes the genetic composition of symbiont populations. Furthermore, host adaptation can result from the evolution of its symbionts, with host and symbiont functioning as a single evolutionary unit.Austrian Science Funds grant: (FWF P27630)

‘Rich’ and ‘poor’ in mentalizing: do expert mentalizers exist?

Mentalization theory is concerned with the capacity to notice, and make sense of, thoughts and feelings in self and others. This development may be healthy or impaired and therefore, by extension, it may be theorized that expertise in mentalizing can exist. Furthermore, a continuum from impairment to expertise should exist within separate dimensions of mentalizing: of self and of others. This study hypothesized that three groups would be distinguishable on the basis of their mentalizing capacities. In a cross-sectional design, Psychological Therapists (‘expert’ mentalizers; n = 51), individuals with a diagnosis of Borderline Personality Disorder (‘poor’ mentalizers; n = 43) and members of the general population (‘non-clinical controls’; n = 35) completed a battery of self-report measures. These assessed the mentalizing of self and of others (using an extended version of the Reflective Function Questionnaire (RFQ18)), alexithymia and cognitive empathy. As hypothesized, Psychological Therapists’ scores were higher than controls on self-mentalizing and control group scores were higher than those with BPD. Cognitive empathy scores in the BPD group indicated markedly lower capacities than the other two groups. Contrary to predictions, no significant differences were found between groups on mentalizing others in RFQ18 scores. The Psychological Therapist and BPD profiles were characterized by differential impairment in self and others but in opposing directions. Results suggest that the RFQ18 can identify groups with expertise in mentalizing. Implications of these results for the effectiveness of psychological therapy and of Psychological Therapists are discussed

Two-dimensional solitons at interfaces between binary superlattices and homogeneous lattices

We report on the experimental observation of two-dimensional surface solitons residing at the interface between a homogeneous square lattice and a superlattice that consists of alternating "deep" and "shallow" waveguides. By exciting single waveguides in the first row of the superlattice, we show that solitons centered on deep sites require much lower powers than their respective counterparts centered on shallow sites. Despite the fact that the average refractive index of the superlattice waveguides is equal to the refractive index of the homogeneous lattice, the interface results in clearly asymmetric output patterns.Comment: 16 pages, 5 figures, to appear in Physical Review