A chamber and artificial dura method for long-term optical imaging in the monkey

Optical imaging over extended periods of time in non-human primates presents serious challenges because the dura mater must be removed to expose the cortical surface. We present a novel nylon imaging chamber with a transparent artificial dura implant, which allows repeated, long-term optical recordings from the cortex. The cylinder of the chamber is inserted into a cranial trephination and held in place with a minimum of screws and acrylic cement. A round patch of artificial dura with a perpendicular wall protects the cortical surface and slows re-growth of dural tissue within the chamber. A cap, manufactured from the same material as the cylinder, is screwed into the chamber and seals it completely. Over a period of 1-4 months, the chamber required a minimum of maintenance and stayed infection-free without local antibiotic application. We repeatedly performed optical imaging in the same animal with the advantages of shortened preparation time. To permit precise alignment and comparison of maps obtained from different imaging sessions, we developed a program that calculated a 2-dimensional spatial transformation between maps of different magnifications, translations, and distortions. We suggest that these methods provide a practical solution to long-term optical imaging in the anesthetized or alert monkey. The exclusive use of non-metallic materials offers the benefit of a lighter and more compact implant, and the possibility to perform MRI scans after chamber implantation.