Simultaneous Evoked Potentials-fMRI acquisition in the rat

Electrophysiological and fMRI recording methods have been used independently to study neural functions. Electrophysiological method has high temporal resolution and fMRI has good spatial views. It would be very helpful if both methods can be utilized on the same animal, preferably simultaneously. However, fMRI use rapidly changing gradient fields and RF pulses, it causes very strong interference in the neural signal. The purpose of the present study was to record blood oxygenation level dependent (BOLD) and somatosensory evoked potentials (SEP) changes simultaneously following electrical forepaw stimulation in alpha-chloralose anesthesized rats. SEP was recorded from glass electrode inserted in the primary somatosensory cortex of the rat. We using twisted and shielded silver wires, and a combined differential pre-amplifier and analog filter processing of neural signal. The artifacts power was minimized by an average of 15.S dB. To minimal distortion due to susceptibility problems caused by drilled holes for intracranial recording, gel was used to cover the holes and nearby skull surface. Under unilateral electrical stimulation of the right and left forepaw, there was no statistically significant difference in the BOLD responses between electrode implanted and non-electrode implanted hemisphere. But activated pixel numbers in the primary somatosensory cortex of the implanted side had about 34% decrease of BOLD signal. Therefore, we have shown here that by several modifications, a simple and feasible methods for simultaneous fMRI and SEP recording experiment for investigating the neural functions is possible.