Putting the puzzle together: From motor to language function

Speaker: Dr Carolin Weiss Lucas - University of Cologne, Germany

The advantages and challenges of combining non-invasive functional mapping techniques and dMRI for understanding functional networks.

The integration of different functional localiser methods such as functional magnetic resonance imaging (fMRI) and neuronavigated transcranial magnetic stimulation (TMS) with advanced structural imaging techniques such as diffusion MRI have helped not only to gain deeper insights into the network functionality of the human brain but also to focus the neurosurgeons' view on clinically most relevant brain functions. Aiming at function-preserving but gross-total resection of intrinsic brain tumours, the use of non-invasive functional localizer techniques and, in particular, TMS allows for accurate delineation of the primary motor cortex (M1), as compared to the gold standard of intraoperative, direct cortical stimulation. Moreover, using TMS for optimised definition of the cortical seeding regions of interest for tractography of the cortico-spinal tract is of particular benefit in the presence of brain tumours. As compared to the mapping of upper and lower limb motor functions, however, the accurate localisation of higher cognitive functions such as language are far more challenging, being based on immediate inhibitory TMS effects during “online” task performance. Despite the attempts of several groups to integrate language mapping techniques based on repetitive TMS (5-10 Hz pulse repetition rate) into presurgical diagnostics, their clinical benefit is yet questionable due to several limitations of the current methodology. Here, evidence from preclinical studies combining fMRI and different repetitive TMS pulse designs suggest that higher rTMS repetition rates might allow for more efficient online inhibition of task performance and, thus, significant reduction of discomfort by using lower stimulation intensities. The validity of such language mapping results, however, remains to be investigated in clinical studies.