1. An apparatus for targeting delivery of a treatment chemical to a target region of the brain of a subject, the apparatus comprising: a storage medium on which is stored digital representations of one or more subject-specific selective visual stimuli that selectively stimulate blood flow to the target area of the brain when viewed by the subject; and an electronic display device coupled to the storage medium and configured for converting the stored digital representations to images viewable by the eye of the subject; wherein the one or more selective visual stimuli were determined by exposing the subject to a plurality of potential stimuli; measuring, for each potential stimulus, the blood flow response to multiple regions of the brain of the subject, including the target area and one or more non-target areas; comparing the blood flow responses to the potential stimuli, and selecting as selective stimuli one or more of the potential stimuli that result in relatively more blood flow to the target area and relatively less blood flow to at least one of the one or more non-target areas when the subject is exposed thereto.