Side effects of transcranial magnetic stimulation biased task performance in a cognitive neuroscience study

Transcranial magnetic stimulation (TMS) is increasingly used as a research tool for functional brain mapping in cognitive neuroscience. Despite being mostly tolerable, side effects of TMS could influence task performance in behavioural TMS studies. In order to test this issue, healthy subjects assessed the discomfort caused by the stimulation during a verbal working memory task. We investigated the relation between subjective disturbance and task performance. Subjects were stimulated during the delay period of a delayed-match-to-sample task above cortical areas that had been identified before to be involved in working memory. Task performance and subjective disturbance due to side effects were monitored. The subjects' grade of discomfort correlated with the error rates: the higher the discomfort, the more errors were made. Conclusively, TMS side effects may bias task performance in cognitive neuroscience studies and may thereby lead to misinterpretation of results. We emphasize the importance of controlling side effects of the stimulation as a source of biasing effects in TMS studies

Tomophobia, the phobic fear caused by an invasive medical procedure - an emerging anxiety disorder: a case report

<p>Abstract</p> <p>Introduction</p> <p>Tomophobia refers to fear or anxiety caused by forthcoming surgical procedures and/or medical interventions.</p> <p>Case presentation</p> <p>We present the case of a 69-year-old Caucasian man who refused urgently indicated medical intervention because of severe tomophobia.</p> <p>Conclusion</p> <p>Due to the rising number of surgical interventions in modern medicine, as well as the high number of unrecognised cases of tomophobia, this common but underdiagnosed anxiety disorder should be highlighted.</p

Transcranial magnetic stimulation in motor conversion disorder: a short case series

The neurophysiologic mechanisms involved in nonorganic paralysis are unclear. Because there is no established standard therapy, the authors investigated the effect of repetitive transcranial magnetic stimulation (rTMS) in four patients with nonorganic limb paralysis. Within the framework of a treatment trial, the patients were treated over a period of 5-12 weeks with rTMS applied to the contralateral motor cortex. Stimulation frequency was 15 Hz, train length 2 seconds, intertrain interval 4 seconds; daily total number of stimuli 4000. In one patient, motor function was completely restored; two patients experienced a marked improvement correlating with rTMS treatment. By contrast, one patient who had been diagnosed as a malingerer did not improve. Apart from possible favorable psychological factors that could partly explain the rTMS-associated effects, high-frequency rTMS might have enhanced or substituted an insufficient input to the motor cortex from failing frontal executive areas, and thereby opened the way to a learning process that lead to the reacquisition of limb use. rTMS may have a therapeutic effect in motor conversion disorder and may help elucidate neurophysiologic aspects of this condition. The potential benefit of rTMS in motor conversion disorder should be evaluated in larger, controlled samples

Continous theta-burst stimulation over the dorsal premotor cortex interferes with associative learning during object lifting

When lifting objects of different mass, humans scale grip force according to the expected mass. In this context, humans are able to associate a sensory cue, such as a colour, to a particular mass of an object and link this association to the grip forces necessary for lifting. Here, we study the role of the dorsal premotor cortex (PMd) in setting-up an association between a colour cue and a particular mass to be lifted. Healthy right-handed subjects used a precision grip between the index finger and thumb to lift two different masses. Colour cues provided information about which of the two masses subjects would have to lift. Subjects first performed a series of lifts with the right hand to establish a stable association between a colour cue and a mass, followed by 20sec of continuous high frequency repetitive trancranial magnetic stimulation using a recently developed protocol (continuous theta-burst stimulation, cTBS) over (i) the left primary motor cortex, (ii) the left PMd and (iii) the left occipital cortex to be commenced by another series of lifts with either the right or left hand. cTBS over the PMd, but not over the primary motor cortex or O1, disrupted the predictive scaling of isometric finger forces based on colour cues, irrespective of whether the right or left hand performed the lifts after the stimulation. Our data highlight the role of the PMd to generalize and maintain associative memory processes relevant for predictive control of grip forces during object manipulation

Accuracy of stereotaxic positioning of transcranial magnetic stimulation

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