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Anatomical reconstruction of a rhesus macaque skull and brain based on a structural magnetic resonance image. Red dots indicate stereotaxic locations of electrodes implanted on the surface of the skull beneath the scalp and muscle tissue to measure the electroencephalogram (EEG) . The goal of this research is to compare directly human and monkey EEG and event-related potentials (Woodman et al. 2007). This surgical method allows accurate comparisons between EEGs by ensuring that the underlying electrical signals propagate through similar layers of tissue and bone in both species. The electrode locations mimic the international 10-20 electrode coordinate system used in human EEG research (Jasper, 1958). First, a template of the adapted macaque 10-20 system was created by measuring electrode distances on a model skull. Second, stereotaxic positions of each proposed electrode location were recorded with accuracy in tens of microns, along with the locations of several anatomical landmarks. Third, during surgical implantation, the same anatomical landmarks were located allowing the electrode template to be rescaled to fit the size of the subjects skull. Finally, the anatomical landmarks measured during the procedure were located in a MRI taken prior to the operation, and used to guide virtual placement of electrodes based on surgical records. The voltages recorded from these electrodes while monkeys perform cognitively demanding tasks will allow researchers in Jeffrey Schall and Geoff Woodman's laboratories to construct scalp surface potential maps and perform dipole source localization necessary to understand how intracranial measures recorded from monkeys relate to extracranial measures recorded from humans.

David Godlove
2010 VRN Cover Award