Scalp EEG Monitoring in Rat Model

In one group of rats, scalp electrodes were used to monitor EEG changes during the experiments. To avoid possible stress effects following invasive surgical implantation, we recorded the EEG from 9 mm stainless steel EEG needle electrodes inserted into the scalp during anesthesia so that they were touching the outer table of the skull. This technique is used for EEG monitoring intraoperatively in humans. After rats were anesthetized with 2% isoflurane and IV catheter insertion, two scalp electrodes [Astro-Med/ Grass Technologies] were placed, as shown in Fig 2. We drew a line between the anterior edge of bilateral ears, likely between Bregma and Lambda [25 (link)]. From the midpoint, one electrode was placed anteriorly perpendicular to the line and the other one was placed posteriorly perpendicular to the line. Two EEG channels were recorded, the first one from an electrode placed over the anterior portion of the brain, and a second electrode placed over the posterior portion of the brain. The EMG was obtained from an electrode placed over the left shoulder, all referenced to an electrode placed near the snout. A ground electrode was placed on the dorsal neck. These three channels were recorded with an A/D rate of 500 Hz/channel, with a 0.05–100 Hz bandpass and 12 dB/octave roll-off. Potentials were amplified with a Neuroscan SYNAMPS 2 system (Compumedics, Inc., Charlotte, NC).