Techniques for improving stereotaxic accuracy in Macaca fascicularis.

Sources of stereotaxic variability in long-tailed macaques (Macaca fascicularis) were examined by X-ray techniques. Accuracy in the vertical dimension can be improved significantly by measuring from the top of the brain rather than from the Frankfurt plane established by external bony landmarks. Even greater accuracy in both the vertical and anterior-posterior dimensions can be attained by rotating the cranium in the stereotaxic instrument to bring the intercommissural line, as defined by ventriculography, into a plane parallel to the horizontal stereotaxic plane, thus approximating the orientation of the brain as represented in both of the brain atlases currently available for this species. An adjustable eyebar spacer, which allows the cranium to be rotated in the stereotaxic instrument, is described.