title: Transcranial magnetic stimulation intensities in cognitive paradigms.
abstract: BACKGROUND
  Transcranial magnetic stimulation (TMS) has become an important experimental tool for exploring the brain's functional anatomy. As TMS interferes with neural activity, the hypothetical function of the stimulated area can thus be tested. One unresolved methodological issue in TMS experiments is the question of how to adequately calibrate stimulation intensities. The motor threshold (MT) is often taken as a reference for individually adapted stimulation intensities in TMS experiments, even if they do not involve the motor system. The aim of the present study was to evaluate whether it is reasonable to adjust stimulation intensities in each subject to the individual MT if prefrontal regions are stimulated prior to the performance of a cognitive paradigm.
  
  
  RESULTS
  Repetitive TMS (rTMS) was applied prior to a working memory task, either at the 'fixed' intensity of 40% maximum stimulator output (MSO), or individually adapted at 90% of the subject's MT. Stimulation was applied to a target region in the left posterior middle frontal gyrus (pMFG), as indicated by a functional magnetic resonance imaging (fMRI) localizer acquired beforehand, or to a control site (vertex). Results show that MT predicted the effect size after stimulating subjects with the fixed intensity (i.e., subjects with a low MT showed a greater behavioral effect). Nevertheless, the individual adaptation of intensities did not lead to stable effects.
  
  
  CONCLUSIONS
  Therefore, we suggest assessing MT and account for it as a measure for general cortical TMS susceptibility, even if TMS is applied outside the motor domain.
authors: Department of Cognitive Neurology, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany.
authors: Jakob A
authors: JA
authors: Kaminski
authors: Franziska M
authors: FM
authors: Korb
authors: Arno
authors: A
authors: Villringer
authors: Derek V M
authors: DV
authors: Ott
mesh_terms: D000328:Adult; D001519:Behavior; D001931:Brain Mapping / Q000379:methods*; D002540:Cerebral Cortex / Q000473:pathology; D016000:Cluster Analysis; D003071:Cognition; D005625:Frontal Lobe / Q000473:pathology; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D008954:Models, Biological; D015233:Models, Statistical; D009044:Motor Cortex / Q000473:pathology; D012044:Regression Analysis; D015203:Reproducibility of Results; D050781:Transcranial Magnetic Stimulation / Q000379:methods*