Abstract

Introduction

Materials & Methods

Results

Discussion & Conclusion

References

Discussion
Board

We have combined stereotactic Transcranial Magnetic Stimulation (TMS) with High-Resolution EEG (Ilmoniemi et al. 1997, NeuroReport 8, 3537-3540). This combination offers several new possibilities in the study and monitoring of the brain: 1) Direct measurement of the electrophysiological cortical response to TMS, 2) Studies of how TMS-induced functional lesions affect sensory evoked potentials and spontaneous EEG activity, and 3) Real-time monitoring of the effects of TMS or rTMS on TMS-evoked brain activity. Using our 60-channel HR-EEG system designed to function during TMS (Virtanen et al. 1998), we have observed the locally induced activity as well as the spreading of the evoked activity. We have used dipole modeling and minimum-norm estimation to locate the activity at different latencies after the pulse. Strong local EEG deflections are observed just milliseconds after the TMS pulse, while the ipsi- and contralaterally spreading neuronal activity can be seen for a period lasting up to 300 ms or more. The local response provides an index of reactivity of the cortex while distant activity gives a measure of connectivity. We have also demonstrated that TMS stimulation can affect the dynamics of sensory evoked auditory and somatosensory potentials (Karhu et al., in preparation; Tiitinen et al., submitted).

Back to the top.
Poster Number PAilmoniemi0651
Keywords: tms, cortex, connectivity, eeg, magnetic