Transcranial magnetic stimulation combined with EEG: a new brain imaging tool

The authors have developed frameless stereotaxy for applying TMS to a given spot in the brain as determined by MRI. They have used high-resolution EEG (HR-EEG) with 60 channels to monitor and locate the TMS-induced activity so that excitability of the different portions of the cortex and connectivity between different areas can be mapped reliably. By using dipole modeling and minimum-norm estimation, the authors have observed both ipsi- and contralateral spreading of neuronal activity after a TMS pulse. They have also demonstrated that TMS stimulation can affect the dynamics of sensory evoked auditory and somatosensory potentials. They expect that the combination of TMS and HR-EEG will offer a powerful tool for basic neuroscience and for clinical diagnosis, for example in the assessment of brain connectivity in patients suffering from neurodegenerative diseases or head injuries.