Background
The present study used magnetoencephalography (MEG) to investigate the neural substrates for modified version of Treisman’s visual search task.
Methods
Two volunteers who gave informed consent participated MEG experiment. One was 27- year old male and another was 24-year-old female. All were right handed. Experiment were performed using a 306-channel biomagnetometer (Neuromag LTD). There were three task conditions in this experiment. The first was searching an open circle among seven closed circles (open condition). The second was searching a closed circle among seven uni-directionally open circles (closed condition). And the third was searching a closed circle among seven eight-directionally open circles (random (closed) condition). In one run, participants performed one task condition so there were three runs in one session of experiment. During one session, 128 trials were performed during every three runs. One participant underwent one session of experiment. The participant pressed button when they found targets. Magnetic source localization images were generated using software programs that allowed for interactive identification of a common set of fiduciary points in the MRI and MEG coordinate frames.
Results
In each participant we can found activations of anterior cingulate, primary visual and association cortices, posterior parietal cortex and brain areas in the vicinity of thalamus.
Conclusions
we could find activations corresponding to anterior and posterior visual attention systems.

Magnetoencephalography (MEG), the measurement of magnetic field produced by neuronal current associated with normal and pathologic brain activities, is a totally noninvasive method for localizing functional regions of the brain. During the past several years, may clinical research centers are working to expand various fundamental functional brain regions, which can be easily localized, as well as to characterize magnetic abnormalities which accompany a wide variety of cerebral disease. At present, MEG is used in a number of clinical centers throughout the world for the presurgical functional localization of eloquent cortex, and for the non-invasive localization of epileptiform activity. And also, non-invasiveness means that it can be used for screening and repetitive of follow-up measurement without concern for adverse effects. As procedures for activating various functional brain regions are standardized, and as the effects of specific cerebral disease on the MEG are carefully documented in controlled studies, the number of routine neurological applications for MEG will increase significantly. In this paper, the basic principles of MEG are reviewed briefly with its clinical application to neurologic disease.

Background
s: MEG can measure the task-specific neurophysiologic activity with good spatial and time resolution. Language lateralization using noninvasive method has been a subject of interest in resective brain surgery. We purposed to develop a paradigm for language lateralization using MEG and validate its feasibility.
Methods: Magnetic fields were obtained in 12 neurosurgical candidates and one volunteer for language tasks, with a 306 channel whole head MEG. Language tasks were word listening, reading and picture naming. We tested two word listening paradigms:semantic decision of meaning of abstract nouns, and recognition of repeated words. The subjects were instructed to silently name or read, and respond with pushing button or not. We decided language dominance according to the number of acceptable equivalent current dipoles (ECD) modeled by sequential single dipole, and the mean magnetic field strength by root mean square value, in each hemisphere. We collected clinical data including Wada test.
Results: Magnetic fields evoked by word listening were generally distributed in bilateral temporoparietal areas with variable hemispheric dominance. Language tasks using visual stimuli frequently evoked magnetic field in posterior midline area, which made laterality decision difficult. Response during task resulted in more artifacts and different results depending on responding hand. Laterality decision with mean magnetic field strength was more concordant with Wada than the method with ECD number of each hemisphere.
Conclusions: Word listening task without hand response is the most feasible paradigm for language lateralization using MEG. Mean magnetic field strength in each hemisphere is a proper index for hemispheric dominance.