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Introduction A previous study ( Hartwigsen et al., 2010 ) has shown that 10 Hz rTMS of the left or right posterior inferior frontal gyrus (IFG) impaired performance in a phonological decision-making task. However, it is unclear whether the neurodisruptive effect of 10 Hz-rTMS is caused by entrainment of alpha-oscillations. To address this issue, the present study investigated the following questions: (1) Are alpha-oscillations in the IFG functionally relevant for phonological processing? (2) Can we enhance alpha activity in the IFG using 10 Hz tACS? and (3) Does enhancement of alpha activity cause behavioral disruption? Methods 24 right-handed, healthy participants (12 male, age range: 18–30 years, mean = 21.96, SD = 3.36) participated in the study. 9 mm2 circular sponge electrodes were placed over the bilateral IFG. In three separate sessions, 1 mA tACS at 10 Hz or 16.18 Hz or sham stimulation were applied for 20 min. Before and after stimulation, 5 min of resting state EEG was recorded. The phonological task required the subjects to indicate via button press whether highly frequent German nouns like ‘Zebra’ consisted of two or three syllables. In a simple control task, participants had to indicate whether an arrow pointed left or right to control for unspecific effects. Results (1) Stimulation was a significant predictor for decision speed in the phonological task (p = .02). Specifically, participants responded faster after 10 Hz relative to sham stimulation, but not after 16.18 Hz. (2) This effect was task specific as tACS did not significantly affect the control task (p = 0.43). (3) Participants had an increase in resting state alpha power (p = .004), which wasn’t modulated by stimulation (p = .70). (4) We found a significant event related desynchronization in the alpha band (p Conclusion The results show an improvement in a phonological word task after applying 10 Hz tACS over the bilateral IFG but not in simple motoric control task. This might be explained by a paradoxical facilitation effect, resulting in an ‘optimal’ level of noise for task processing ( Miniussi et al., 2013 ) or by inhibition of surrounding areas that might be competing for task resources. Since no specific effect on alpha oscillations could be found, further studies will therefore investigate effects of focal online stimulation.

Introduction Semantic integration refers to the influence of previous context on the automatic integration of new information into a sentence during word comprehension. Neuroimaging studies have shown that sentence-level integration of semantic information is associated with activation of a left-lateralized fronto-temporal language network (Baumgaertner et al., 2002). The activation patterns are dependent on the difficulty of semantic integration which can be operationalised on the sentence-level through variation of the terminal word's expectancy, called "cloze probability". With this paradigm we attempted to characterize the properties of the language network relevant for semantic integration through multimodal neuroimaging examining structural and effective connectivity. Methods 17 young and healthy right-handed individuals were examined with functional MRI (fMRI) while they judged aurally presented sentences. Sentences were constructed following the pattern "Der Schreiner baut den … (The Carpenter constructs the …) Tisch (desk=expected)/Turm (tower=unexpected)/Wein (wine=incongruent)/Kirst (pseudo word=anomalous)". In a lexical decision task the subject has to decide if the last word of a sentence is a word ("Tisch"/"Turm"/"Wein") or a pseudo word ("Kirst"). Dynamic causal modeling (DCM) for effective connectivity was calculated for 63 fully connected models between fMRI activation maxima in three regions. Additionally diffusion tensor imaging (DTI) sequences were acquired to assess structural connectivity between these regions. Results Behavioural data show the expected influence of cloze probability on lexical decision reaction times (expected nouns expected and incorrect>expected activation in the left inferior frontal gyrus (IFG) and the superior and medial temporal gyrus (STG/MTG) was increased ( p Discussion These results support the notion of a key contribution of the inferior frontal gyrus and the medial and superior temporal gyrus to semantic integration. DCM network analysis shows inhibitory influences on the pMTG as a consequence of increased difficulty of semantic integration. The functional relevance of these activation patterns and interactions will now be addressed in TMS experiments.

Using non-invasive stimulation techniques in the healthy human brain allows for the investigation of acute focal “lesion” effects that are not confounded by chronic processes mediating functional recovery. In this talk, I will outline how TMS can be used to characterize the involvement of homologous right hemisphere brain regions in language. The first part of my talk focuses on the use of multifocal dual-site “online” TMS approaches in which TMS is applied either unilaterally over homologous areas in the left or right hemisphere or simultaneously to both hemispheres during different language comprehension tasks. Here, online TMS is used to characterize the contribution of the stimulated area to a specific language function. The dual-site TMS approach further offers the possibility to study interhemispheric compensation by comparing the effects of unilateral TMS over either hemisphere with the effects of bilateral stimulation. I will also introduce the “condition-and-perturb” TMS approach which combines the application of offline and online TMS over different nodes within a functional network. This approach allows for the investigation of intact interactions and adaptive short-term reorganisation processes within intrahemispheric language networks. The second part of my talk focuses on the combination of offline TMS (i.e., TMS before a task) and functional MRI to investigate compensatory short-term reorganisation and changes in effective connectivity in the language network.