Materials and Methods 1 Animal Subjects

Anesthesia was induced by ketamine (10 mg/kg IM) and atropine (0.04 mg/kg SC) and maintained using 1-2% isoflurane. Pulse and arterial oxygen saturation were measured using a magnet-compatible pulseoximeter. Blood pressure was determined on demand using a remotely triggerable pediatric cuff (Invivo Research, Orlando, FL). Respiration was monitored by direct sight of the animal’s chest and by observation of a respiration bladder placed in line with the endotrachial tube. Cortical recording chambers were filled with a solution of 5 mg/mL gadopentetate dimeglumine (trade name Magnevist from Berlex Laboratories, Wayne, NJ).

IV.2.3.2 MR Imaging

Magnetic resonance (MR) imaging was performed on a 3 T Siemens Trio scanner with 40 mT/m gradients (200 µs rise time) using an 8-channel high-resolution head array coil (MRI

Devices, Waukesha, WI) as a transceiver. Anatomical images were acquired using a slice- selective saturation recovery magnetization-prepared rapid-acquisition gradient echo sequence (TR 1400 ms, TE 3.49 ms, TI 670 ms, 12 deg flip angle, 170 Hz/Px bandwidth.) 160 images were acquired sagittally with 0.7 mm slice thickness using an in plane field of view of 168 x 168 mm on a 256 x 256 base matrix, yielding a final native voxel resolution of 0.656 x 0.656 x 0.7 mm. These images were realigned via multi-planar reformat to recording chamber landmarks using Siemens Syngo software (version MR 2003T DHHS.) This rotated volume was resliced at 0.7 mm spacing along the z-axis of the chamber and visualized using the AFNI software package (Cox, 1996a). 3D rendering was accomplished using the BrainVoyager software suite (Brain Innovation, Netherlands.)

IV.2.4 Results

Magnetic resonance imaging of three macaque monkeys (R, S and T) was performed after each animal had been a subject in multiple electrophysiological recording experiments. Monkey T was imaged to determine the orientation of electrodes placed within a single lateral recording chamber. Monkeys R and S each had two recording chambers, a midline chamber placed anterior to the intra-aural line and a parietal chamber. Here, the relative position of each animal’s midline/anterior chamber is compared. Although all animals had numerous metallic implants, not limited to anchor screws, headposts and electrical connectors, all artifacts produced by these materials were sufficiently far from the chamber to produce little or no difficulty in interpreting the images. All image volumes were aligned to the long axis of the recording chamber and zeroed to the chamber center to

73 facilitate use by the researcher in determining chamber coordinates of a single penetration.

For monkey T, an image was chosen deep ( ~7 mm) to the surface of cortex which provided clear presentation of the superior temporal and lateral sulci (Figure IV.2.1.) The site of electrode recording was determined to be on the surface of the superior temporal gyrus adjacent to the most posterior aspect of the lateral sulcus. A rendered surface of the animal’s head confirms the extreme lateral positioning of the chamber and aids in the visualization of the recording site (Figure IV.2.2.)

Electrode tracks from monkeys R and S are depicted in cross section (Figures IV.2.3 and IV.2.4) and by a deep plane (Figures IV.2.5 and IV.2.6). The cross-sectional images show the extent of the chamber walls and the central axis of the chambers, representing the span of cortical surface on either side of the midline available for recording. The deep planes represent the whole area of the chamber shown in reference to the surrounding sulci. For monkeys R and S, deep levels (~8-10 mm) were chosen to clearly show the arcuate, primary and central sulci. Three-dimensional rendering of each animal (Figures IV.2.7 and IV.2.8) allows the recording sites to be compared easily and with additional physiologic cues.

IV.2.5 Summary

Anatomical imaging using a 3T Siemens Trio MRI system was performed on three macaque monkeys previously used in cortical electrophysiology experiments. All three

subjects had a previously mounted head restraint containing a recording chamber. For the purposes of imaging, the chamber was filled with a gadolinium contrast agent (as gadopentetate dimeglumine) which facilitated visualization of the inner volume. Images were reconstructed in plane with the axis of the chamber and rendered in 2D flat slices and 3D whole head reconstructions. Projections of the extent of the chamber walls were used to determine the central point of the chamber, which would directly correspond to microdrive coordinates used in experimental placement of the electrode. Multiple sites of electrode positions could be discerned by examination of the images for small susceptibility defects left along the track of a recording penetration. Comparison between animals with chambers thought to be positioned similarly allows for the clear and precise determination of variations of placement and anatomy between the subjects. For measurements taken at the surface of cortex, a deep plane was used for actual localization due to the ease in viewing the relative positions of surrounding landmarks. The 3D rendered images sacrifice an orthogonal presentation of the image plane for additional information such as easy visualization of the anterior-posterior orientation which may aid a viewer. Additionally, visualization of recording chambers placed at extreme angles may benefit from the 3D reconstruction as 2D images are likely to be wholly different from commonly understandable stereotaxic sections.

IV.2.6 Acknowledgement

Thanks go to Betty Gillikin, Kelsie Pejara and Lea Martin for assistance with animal handling. Steve Flaherty provided technical assistance during the scanning sessions. This

75 work was funded in part by a James G Boswell Professorship, a medical scientist training program grant from the National Institutes of Health and the UCLA Aesculapians, and an ARCS Fellowship.