IN-VIVO MICROELECTRODE LOCALIZATION IN THE BRAIN OF THE ALERT MONKEY - A COMBINED RADIOGRAPHIC AND MAGNETIC-RESONANCE-IMAGING APPROACH

A technique is described for in vivo localization of microelectrodes d uring single-unit recording in the alert monkey. Four hollow glass sph eres filled with copper sulfate and iohexol were affixed to the surfac e of the animal's skull prior to the acquisition of a series of corona l magnetic resonance (MR) images. These reference beads were visible i n both X-ray and MR images. Cranial recording chambers were then impla nted bilaterally over the amygdaloid complex. A microelectrode was adv anced to various depths in the subject's brain. At each selected micro electrode site, five radiographs were obtained and a small electrolyti c lesion was made. Based on the data from the radiographs, we computed the position of the microelectrode tip at each site relative to the r eference beads. With a precision of 625 mu m, this method was used to predict the neuroanatomical location of ten microlesions placed in bot h subcortical and cortical structures. Postmortem histological analysi s revealed that the actual location of the lesions closely matched pre dictions arrived at using the X-ray/MRI localization technique. This t echnique thus provides an accurate, reliable and noninvasive method fo r in vivo localization of microelectrode recording sites.