P 57. Continuous theta burst stimulation in a cognitive task: Virtual lesion comparable to 1 Hz TMS?

Abstract

Introduction Repetitive transcranial magnetic stimulation (rTMS) in form of theta burst stimulation (TBS) is a potent tool to modulate motor cortex function. Several studies demonstrate effects of TBS on non-motor cortical areas. However, it is not yet clear whether TBS can change network properties in any cortical area. Objectives To compare continuous TBS with 1 Hz rTMS as a tool to induce a virtual lesion in a cortical region. We chose the left superior temporal cortex and tested responses in a lexical decision task. Materials and methods Four groups with 20 subjects each were stimulated. In the 3 experimental groups the stimulation site, the posterior part of the left superior temporal sulcus (Brodmann areas 22 and 21) was identified in an individual anatomical MRI scan and coil position was adjusted with neuronavigation. Stimulation was either 20 min of 1 Hz rTMS at 100% resting motor threshold (RMT) or continuous TBS (600 pulses), with intensities of 80% or 90% active motor threshold (AMT), respectively. The TMS-control group was stimulated at right medial prefrontal cortex (Brodmann area 9) with 1 Hz rTMS. After stimulation subjects accomplished a lexical decision task consisting of 100 German words and 100 pseudowords of comparable word length (6 letters on average). Overall duration was about 20 min. In an additional fifth group of 20 subjects the lexical decision task was performed without TMS. Reaction times and error rates were analyzed. Results Reaction times were not influenced by cTBS applied with 80% AMT, but prolonged for about 80 ms with 90% AMT compared to the no stimulation condition. An increase of 140 ms was found after 1 Hz rTMS. The effect lasted for the whole task, but declined from first to second half of the experiment. Non-specific effects after stimulation of right medial prefrontal cortex were not observed. Conclusion The direct comparison of cTBS and 1 Hz rTMS suggest that both stimulation pattern can induce virtual lesions in left superior temporal cortex and impair semantic processing. We suppose that cTBS could replace 1 Hz rTMS in this field since application is faster and it is more comfortable to the subjects.