the present invention is a method and composition for treatment of ischemic , metabolic , congenital , or degenerative disorders of the central or peripheral nervous system . the composition is formed by encapsulation within an implantable biocompatible polymeric device of one or more compounds which have the effect or replacing or stimulating functions of the nervous system . a variety of biocompatible polymers including both biodegradable and non - degradable polymers can be used to form the implants . an essential feature of the composition is linear release , achieved through manipulation of the polymer composition and form . the selection of the shape , size , drug , polymer , and method for implantation are determined on an individual basis according to the disorder to be treated and the individual patient response . a plethora of neurally active substances can be used to treat or manipulate neurological disorders , including parkinson &# 39 ; s disease , particularly the subset which is refractory or poorly responsive to existing therapies ; alzheimer &# 39 ; s disease ; huntington &# 39 ; s disease ; and trauma , such as spinal cord injury .