Measurement of magnetic fields and current source localization in auditory cortical activity of rats by a 12-channel dc-SQUID gradiometer

Most of the previously reported studies on the auditory brain function of small animals used invasive techniques, such as the insertion or placement of electrodes in the cortex [1]. The invasive measurement is applied to studies on shortterm experiments because maintaining optimum conditions for a long period of time is difficult in small animals. This study focused on the noninvasive measurement and localization of the auditory cortical activation in the rat brain. The weak auditory evoked magnetic fields of up to 1 pT order with a 7.5 mm spatial resolution were measured using a 12-channel highresolution DC-SQUID magnetometer. The distribution of magnetic fields was analyzed, and the source of the auditory activity was localized by iterative minimum norm estimation (MNE) [2,3]. The global average and the histogram of the current sources were calculated statistically.