Study of activated area in the brain as sources of MEG and fMRI

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This research aims at development of functional imaging of the brain which has the feature of the high spatial resolution and the high temporal resolution. The aim of this study is clarifying the relevance of nerve activity and a hemodynamics of the brain, and the relevance of the excitability of the electric activity within a brain, and the MEG and EEG. Moreover, the result obtained by magnetoencephalography and fMRI was compared and investigating change of a spatial and temporal signal and both relevance also inquired as a purpose. For an animal experiment, a high spatial resolution SQUID system was developed. This SQUID system enabled to measure and discriminate the magnetic field pattern under 800 μm resolution. It is possible to measure the magnetic activity at a tissue level with cellular-scale spatial resolution. Using this SQUID system, magnetic Fields produced by the compound nerve action current of the frog's sciatic nerve could be measured. Moreover, measurement of auditory … More evoked magnetic fields of mice within the 2 mm resolution was succeeded. However, it is difficult to estimate the source of MEG, because of the insufficiency of measurement points and low sensitivity. On the other hand, to clarify the relationships between neuronal activity and the hemodynamic response, activations of the primary somatosensory cortex were studied using MEG (magnetoencepahlogram) and fMRI (functional magnetic resonance imaging). Effects of the stimulus intensity of the electrical stimulation to the right thumb were investigated. When the stimulus intensity increased to the pain feeling in the fMRI experiments, a number of activated pixels and signal power which was defined as the integration value of NMR signal were increase steeply, however, this inclination did not correspond to neuronal activity. An increase of blood flow at the SI area continued for a longer duration and spread widely when the subject experienced pain exposed to strong stimulation. Neuronal activity at the SI area caused within 100 ms and did not spread widely even if the subject experienced pain. We also studied the short-term episodic memory using MEG and EEG. Sourece estimation showed a significant activation in the left inferior medial temporal lobe related to intentional encoding prosesses. Less