Typically, anatomical connections have been traced by injecting pathwa
y-tracing chemicals into restricted portions of the brain. After a few
days, the brains are fixed and the transported chemicals identified i
n histological sections. Orthograde tracers move forward along axons f
rom cell body to axon terminals and retrograde tracers move backwards
along axons from terminals to parent cell body. The use of both types
of tracers has revealed origins and terminations of pathways and a mas
sively complex network of connections between numerous functionally an
d anatomically distinct cerebral cortical and subcortical regions. In
the monkey visual system alone more than 300 connections have been des
cribed between the 32 visual cortical areas. Even so, in the network d
escriptions neither anatomical strengths nor functional impacts of ind
ividual connections are identified. Yet, there is no doubt that knowle
dge about both aspects of connectivity is essential for developing acc
urate descriptions of network operations. We describe a new combinatio
n of a metabolic mapping and a reversible deactivation technique in an
animal model to assess the functional impact of cerebral connections.