A METHOD FOR IMPROVING THE ACCURACY OF STEREOTAXIC PROCEDURES IN MONKEYS USING IMPLANTED FIDUCIAL MARKERS IN CT SCANS THAT ALSO SERVE AS ANCHOR POINTS IN A STEREOTAXIC FRAME

We developed a relatively inexpensive method for stereotaxic placement of electrodes or needles in the brains of monkeys. Steel balls were a ffixed to the skulls of monkeys. These balls served as fiducial marker s and were also used as points at which the monkey's skull was held in a modified stereotaxic apparatus. Computed tomography (CT) was used t o establish the location of an injection target with respect to the fi ducial markers. A computer program related the CT coordinates to stere otaxic coordinates. These were used to direct an electrode marker towa rd a target in the hypothalamus. With the marker left in place, the mo nkey was removed from the stereotaxic frame and a second CT scan was p erformed. Corrections for errors in marker placement were made and ret rograde tracers were injected. This procedure was found to be more acc urate and reliable than conventional stereotaxic procedures. The accur acy and repeatability of the technique were also established using a p hantom model of a monkey's skull. Two important advantages of this met hod are that animals can be repeatedly placed into the stereotaxic fra me in precisely the same position and that there are many opportunitie s during the procedure to check for and correct errors. (C) 1997 Elsev ier Science B.V.