Effects of stimulus intensity on fMRI and MEG in somatosensory cortex using electrical stimulation

To clarify the relationship between neuronal activity and the hemodynamic r esponse, activations of the primary somatosensory cortex were studied using MEG(magnetoencepahlogram) and fMRI (functional magnetic resonance Imaging) , Effects of stimulus intensity by electrical stimulation to the right thum b was investigated. We focused on the number of activated pixels, time cour ses of hemodynamic response obtained by fMRI, and dipole moments of neuroma gnetic activity. For fMRI experiments, a number of activated pixels and sig nal power, which was defined as the integrated value of MR signal, greatly increased when an increase in stimulus intensity generated pain. This trend , however, did not correspond to the observed MEG responses. When the stimu lus intensity changed, fMRI responses showed the different tendency of MEG responses.