Carlos Schönfeldt-Lecuona

In cognitive neuroscience, optically tracked frameless stereotaxic navigation has been successfully used to precisely guide transcranial magnetic stimulation (TMS) to desired cortical areas for brain-mapping purposes. Thereby, potential sources of imprecision are the fixation of a reference frame to the head of the subject and the referencing procedure according to certain landmarks (LM). The aim of our study was to evaluate the accuracy of frameless stereotaxic coil positioning in a standard experimental setting. A parameter for accuracy is the reproducibility of LM coordinates. In order to test the stability of the referencing for stereotaxic positioning within a single TMS session (within-session stability), the coordinates of six predefined facial LM in nine subjects were recorded first after the initial registration and second after a 20 minutes TMS session. The two sets of coordinates were then compared. The reliability of the positioning coordinates between different TMS sessions (inter-session repeatability) was addressed by registering the subjects LM coordinates in two independent TMS sessions. The variance of the recorded coordinates was analyzed. Altogether, LM were registered 1728 times (192 measures per subject). Within-session stability: The mean Euclidean distance (MED) between the LM position coordinates before and after a TMS session was 1.6 mm, when pooling over all LM. Inter-session repeatability: The MED between the LM positions recorded after the reference procedures of two different sessions showed an average deviation of 2.5 mm. In conclusion, optically tracked frameless stereotaxic coil positioning is from the technical viewpoint of high stability and repeatability. It is therefore a precise method for TMS brain mapping studies or for repeated TMS treatments, with the need of topographically exact stimulation.

In der ICD-10 und im DSM-IV werden mehrere Störungen definiert, die durch ein Auftreten physischer Symptome ohne entsprechendes „organisches Korrelat“ charakterisiert sind. Konversionsstörungen (DSM-IV) bzw. dissoziative Störungen (IDC-10) sind historisch eng verbunden mit dem Begriff der Hysterie. Ätiopathogenetisch sind sie weitgehend unverstanden. Anknüpfend an psychoanalytische Erklärungsmodelle, beinhalten die modernen deskriptiven Diagnosesysteme in ihrer Definition weiterhin einen Bezug auf einen vorangehenden seelischen Konflikt. In diesem Artikel werden die aktuellen Erkenntnisse klinischer und epidemiologischer Studien zusammenfassend referiert. Erste funktionell bildgebende Untersuchungen erlauben, Hypothesen über zugrunde liegende Mechanismen neurowissenschaftlich zu untersuchen. Der Einsatz und die Resultate dieser Methoden stellen die traditionelle und oft falsch verstandene Dichotomie zwischen „organischen“ und „psychogenen“ Erkrankungen in Frage. The two international systems of diagnostic classification for psychiatric disorders, ICD-10 and DSM-IV, differentiate a variety of disorders or syndromes characterized by the common feature of the presence of physical symptoms without “organic correlate.” Conversion disorders (DSM) or dissociative disorders (ICD) are historically related to the concept of hysteria. Like psychoanalytical theories, the DSM and ICD refer to a psychological conflict preceding the onset of physical symptoms, although in a purely descriptive manner. The etiology of these disorders is still not very well understood. This article summarizes present knowledge from clinical and epidemiological studies. Functional neuroimaging studies on conversion disorders, although still very rare, allow testing of hypotheses about neuronal mechanisms. Such studies question the traditional and often misinterpreted dichotomy between organic and psychogenic diseases.

Background: There is no agreement on the most effective therapy for motor conversion symptoms. Functional electric stimulation has been successfully used to reverse conversion paralysis. We tested the therapeutic potential of high-frequency repetitive transcranial magnetic stimulation (rTMS) in a 20-year-old patient suffering from a conversion paralysis of the right arm. Method: rTMS was applied to the contralateral motor cortex. Stimulations were performed on working days at a frequency of 15 Hz (train length 2 s; inter-train interval 4 s) yielding 4,000 pulses/day. Results: Within 12 weeks, motor function, hyposensibility and muscle bulk were completely restored. Conclusions: The patient recovered completely during rTMS treatment. In addition to possible psychological effects, rTMS may have had a causal therapeutic effect by strengthening corticocortical connections and thereby priming voluntary movements. Further controlled studies are needed.

Die transkranielle Magnetstimulation (TMS) hat sich in den letzten Jahren aufgrund ihrer guten zeitlichen und zufriedenstellenden räumlichen Auflösung sowie der guten Verträglichkeit und Sicherheit und ihrer einfachen Praktikabilität als Forschungsinstrument in den Neurowissenschaften etabliert. Ein grundlegendes Problem bleibt jedoch die optimale Positionierung der Spule zur gezielten und fokussierten Stimulation. Die initial verwendeten Methoden zur Spulenpositionierung (in Anlehnung an das EEG-10-20-System, orientiert am Motorkortex oder an Landmarken) sind mittlerweile durch exaktere, aber auch kostenintensivere stereotaktische Positionierungsmethoden ergänzt worden. Diese neuen Techniken bedienen sich der Bildgebung, insbesondere der Magnetresonanztomographie. Rahmenlose optisch gesteuerte Neuronavigationssysteme können als komfortable und präzise Methode zur Spulenpositionierung angesehen werden. Unser Beitrag stellt verschiedene TMS-Positionierungsstrategien und -methoden vor. In the past years transcranial magnetic stimulation (TMS) has become etablished as research tool in neurosciences due to its characteristics: high temporal resolution, innocuous effect of the magnetic fields and the easy practicability. One of the main difficulties of this method consists in finding the optimal coil position when trying a focused stimulation. The positioning methods initially used, e.g. oriented to the international EEG 10-20 system, oriented to the motor cortex or using specific landmarks, have been complemented by neuronavigational devises in the last years. These techniques are based on individual imaging data aquired prior to TMS. Optical tracked and frameless neuronavigation appears to be, due to its comfortable use and accuracy, the optimal positioning method for foccused TMS. Our manuscript adresses the issue of different coil positioning strategies, advantages and disadvantages.

Die antidepressive Wirkung der repetitiven transkraniellen Magnetstimulation (rTMS) wurde in den letzten Jahren in zahlreichen Studien untersucht. Das Spektrum der Ergebnisse reicht von der Beurteilung der Methodik als unwirksam bis hin zu Besserungsraten um mehr als 50 %. Ein Vergleich der Ergebnisse verschiedener Arbeitsgruppen wird dadurch erschwert, dass sich die meisten Studien hinsichtlich der Stimulationsparameter, der Patientenauswahlkriterien und weiterer Designaspekte voneinander erheblich unterscheiden. Explizit pathophysiologisch begründete Parameter für eine antidepressiv wirksame Stimulation wurden bisher nicht gefunden; dies sollte Thema künftiger Untersuchungen sein, wobei unterstützend auch funktionell bildgebende Techniken herangezogen werden können. Dieser Artikel bietet eine Übersicht der bisher publizierten Studien, eine kritische Analyse der verschiedenen Stimulationsprotokolle und zeigt mögliche Zukunftsperspektiven der antidepressiven TMS auf. The antidepressant effect of repetitive transcranial magnetic stimulation (rTMS) has been studied intensively over the last years. Numerous studies worldwide yielded variable results ranging from ineffectivity to an efficacy rate of more than 50 % for the reduction of depressive symptoms. A comparison of the effectiveness of TMS across studies is difficult due to the variety of chosen stimulation parameters, different inclusion criteria, and different designs. The discrepancies in results could be partially in account to these factors. From a pathophysiological point of view, there are no empirically justified parameters published carrying out an antidepressant TMS. Further studies are required to find optimal stimulation parameters using complementary methods like functional imaging techniques or regarding other factors that could interfere with its efficacy. An overview of studies published in the last ten years, a critical analysis of stimulation procedures and protocols, and possible future perspectives of this method are reviewed in this article.