Extended local access fibers: adjustable treatment of deep sites in the brain

We describe a minimally invasive method for administering diffusible substances to computer-targeted regions of the primate brain. Treatments enter the brain by diffusion or under pressure from the portion of a curvilinear implant that lies within the region of interest. During the implantation surgery, a guide-tube cannula is passed through a cranial burr-hole and concentric, telescoping needles are extended from the cannula in sequence to trace a pre-planned course through brain tissue. After the leading end of the longest needle emerges through another burr-hole, the surgeon fastens a hollow dialysis fiber to its tip and draws the fiber into the brain by retracting the telescoping device in an orderly sequence. The surgery affects brain tissue only along the course of the fiber, causing about the same acute damage as the stereotactic introduction of an ordinary straight needle. The 'extended local access fiber' is relatively soft, flexible, and biocompatible. It remains permanently in the brain, with its semipermeable portion lodged in the target region. Leading and trailing portions are accessible from outside the brain. Experiments indicate a broad range of possible trajectories and confirm that substances delivered by access fiber can have physiological effects even 10 weeks after implantation.