TMS field modelling-status and next steps

In the recent years, an increasing number of studies used geometrically accurate head models and finite element (FEM) or finite difference methods (FDM) to estimate the electric field induced by non-invasive neurostimulation techniques such as transcranial magnetic stimulation (TMS) or transcranial weak current stimulation (tCS; e.g., Datta et al., 2010 and Thielscher et al., 2011). A general outcome was that the field estimates based on these more realistic models differ substantially from the results obtained with simpler head models. This suggests that the former models are indeed needed to realistically capture the field distribution in the brain. However, it is unclear how accurate even these more advanced models are and, in particular, to which extent they allow predicting the physiological outcome of stimulation. An experimental validation of the novel methods for field calculation is thus necessary. Focusing on motor cortex stimulation by TMS, our goal is to explore to which extent the field estimates based on advanced models correlate with the physiological stimulation effects. For example, we aim at testing whether interindividual differences in the field estimates are also reflected in differences in the MEP responses. This would indicate that the field calculations accurately capture the impact of individual macroanatomical features of the head and brain on the induced field distribution, in turn strongly supporting their plausibility. Our approach is based on the SimNIBS software pipeline (www.simnibs.de) that allows for the automatic creation of accurate head models from structural and diffusion-weighted magnetic resonance images (MRI) (Windhoff et al., 2011). This enables us to perform field calculations for multiple subjects, as required in neuroscientific studies. We substantially improved the software in order to improve its usability in a group analysis. At the moment, we are performing field calculations and are acquiring motor mapping data in a group of subjects for a systematic comparison of both data sets. I will give an overview on the status of the SimNIBS project. I will start by summarizing the key findings on how the individual brain anatomy shapes the electric field induced by TMS Thielscher et al., 2011 and Opitz, 2011. The putative link between the modeling results and basic physiological TMS effects is highlighted. I will then introduce the novel features of SimNIBS that include the import of coil positions from neuronavigation systems, improved support for diffusion-weighted MRI and transformation of the estimated fields into MNI space for group analysis. Preliminary results on the comparison between field estimates and motor mapping data will be presented. To summarize, field estimates based on accurate head models have already proven highly useful for a better understanding of the biophysics of non-invasive brain stimulation. The improved software tools now allow for systematic tests of the links between the estimated fields and the physiological effects in multi-subject studies. This will give the knowledge needed, e.g., for a more accurate spatial targeting of specific brain areas by TMS

The Qualification Problem: A solution to the problem of anomalous models

AbstractIntelligent agents in open environments inevitably face the Qualification Problem: The executability of an action can never be predicted with absolute certainty; unexpected circumstances, albeit unlikely, may at any time prevent the successful performance of an action. Reasoning agents in real-world environments rely on a solution to the Qualification Problem in order to make useful predictions but also to explain and recover from unexpected action failures. Yet the main theoretical result known today in this context is a negative one: While a solution to the Qualification Problem requires to assume away by default abnormal qualifications of actions, straightforward minimization of abnormality falls prey to the production of anomalous models. We present an approach to the Qualification Problem which resolves this anomaly. Anomalous models are shown to arise from ignoring causality, and they are avoided by appealing to just this concept. Our theory builds on the established predicate logic formalism of the Fluent Calculus as a solution to the Frame Problem and to the Ramification Problem in reasoning about actions. The monotonic Fluent Calculus is enhanced by a default theory in order to obtain the nonmonotonic approach called for by the Qualification Problem. The approach has been implemented in an action programming language based on the Fluent Calculus and successfully applied to the high-level control of robots

ALPprolog --- A New Logic Programming Method for Dynamic Domains

Logic programming is a powerful paradigm for programming autonomous agents in dynamic domains, as witnessed by languages such as Golog and Flux. In this work we present ALPprolog, an expressive, yet efficient, logic programming language for the online control of agents that have to reason about incomplete information and sensing actions.Comment: 16 page

Agents in proactive environments

Agents situated in proactive environments are acting au-tonomously while the environment is evolving alongside, whether or not the agents carry out any particular actions. A formal framework for simulating and reasoning about this generalized kind of dynamic systems is proposed. The capabilities of the agents are modeled by a set of conditional rules in a temporal-logical format. The environment itself is modeled by an independent transition relation on the state space. The temporal language is given a declarative semantics

Comparing TMS perturbations to occipital and parietal cortices in concurrent TMS-fMRI studies-Methodological considerations

Neglect and hemianopia are two neuropsychological syndromes that are associated with reduced awareness for visual signals in patients' contralesional hemifield. They offer the unique possibility to dissociate the contributions of retino-geniculate and retino-colliculo circuitries in visual perception. Yet, insights from patient fMRI studies are limited by heterogeneity in lesion location and extent, long-term functional reorganization and behavioural compensation after stroke. Transcranial magnetic stimulation (TMS) has therefore been proposed as a complementary method to investigate the effect of transient perturbations on functional brain organization. This concurrent TMS-fMRI study applied TMS perturbation to occipital and parietal cortices with the aim to 'mimick' neglect and hemianopia. Based on the challenges and interpretational limitations of our own study we aim to provide tutorial guidance on how future studies should compare TMS to primary sensory and association areas that are governed by distinct computational principles, neural dynamics and functional architecture

Vergleich der Häufigkeit von spontanen und olfaktorisch evozierten Atemänderungen bei jungen Normosmikern

Die Respirationsolfaktometrie ist eine objektivierende Riechtestung, die häufig im Rahmen von gutachterlichen Fragen durchgeführt wird. Von Januar bis Mai 2013 wurden für die Erstellung der vorliegenden Studie 26 Normosmiker im Alter von 19-35 untersucht. Das Vorgehen gliederte sich in 3 wesentliche Teile: einer Riechtestung mittels Sniffin Sticks, der Beobachtung einer 10-minütigen Ruheatmung und der Untersuchung der Atmung während der Reizung mit Schwefelwasserstoff (2ppm) bzw. Neutralluft. Die Erkenntnis, inwieweit die individuelle Ruheatmung Einfluss auf die Dauer der Respirationsolfaktometrie nimmt und inwiefern es zu respiratorischen Änderungen nach Riechreizung bzw. Neutralluftreizung kommt, war das Ziel dieser Untersuchungen. Schwefelwasserstoff-Reize evozierten signifikant mehr Atemänderungen als Neutralluft-Reize. Nach Neutralluftreizen waren immerhin 20-30% der auf den Reiz folgenden Atemzüge spontan verändert. Spontane Atemänderungen lassen sich in der Regel nicht von evozierten unterscheiden und könnten als Riechwahrnehmung fehlinterpretiert werden. Es sollten deshalb randomisiert Reize mit reinen Riechstoffen und Neutralluftreizen wiederholt in die Ruheatmung appliziert werden, um mehrheitliche Atemänderungen bei olfaktorischer Reizung darstellen zu können