FUNCTIONAL IMPACT OF CEREBRAL PROJECTION SYSTEMS

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.