In this paper, a high resolution SQUID system was used for animal experiments. The auditory evoked magnetic fields of three adult mice were measured. Tone bursts of 2 kHz with 10 ms duration was used as the auditory stimuli. The stimuli were presented to the right ear of the mouse through a plastic tube. Magnetic signals were filtered from 1 to 100 Hz and averaged more than 5000 times. The peak of the magnetic fields appeared at the latency about 20 ms and the large peak appeared at the latency 80 ms. The study showed that it is possible to measure the mice magnetoencephalogaphy (MEG) with adequate spatial resolution. Animal MEG measurement may contribute to the further understanding of the physiological basis of the MEG.
In this paper focused an EEG measurement system enable us to eliminate the electromagnetic interaction emitted from TMS. The EEG activities 5 ms after TMS stimulation were successfully measured. Using this special amplifier, we investigated the intensity dependence of brain activation induced by TMS.
To investigate the relationship between neuronal activity and hemodynamics, we carried out a near-infrared spectroscopy (NIRS) study to measure the regional changes of hemoglobin concentration associated with cortical activation in the human sensorimotor cortex (SMI) to both voluntary and nonvoluntary tasks. We measured the hemodynamic evoked responses to voluntary finger movement and nonvoluntary electrical stimulation applied on the fingers (thumb and ring finger, respectively). Measurements were performed on 6 healthy right-handed volunteers using block paradigms and we analyzed both the spatial/temporal features and the magnitude of the optical signal induced by cerebral activation during these protocols. We constantly observed an increase in the cerebral concentration of oxygenated hemoglobin at the cortical side contralateral to the stimulated side. Our findings are in agreement with results in positron emission tomography (PET), functional magnetic resonance imaging (fMRI) and EEG (Electroencephalogram).
Transcranial magnetic stimulation (TMS) is a method to stimulate neurons in the brain. It is necessary to obtain eddy current distributions and determine parameters such as position, radius and bend-angle of the coil to stimulate target area exactly. In this study, we performed FEM-based numerical simulations of eddy current induced by TMS using three-dimentional human head model with inhomogeneous conductivity. We used double-cone coil and changed the coil radius and bend-angle of coil. The result of computer simulation showed that as coil radius increases, the eddy current became stronger everywhere. And coil with bend-angle of 22.5 degrees induced stronger eddy current than the coil with bendangle of 0 degrees. Meanwhile, when the bend-angle was 45 degrees, eddy current became weaker than these two cases. This simulation allowed us to determine appropriate parameter easier.
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