The brain consists of large neuronal networks that are densely interconnected. Depending on context, task and selective attention, sub-networks become selected such that specific computations are performed, which ultimately lead to appropriate behavioral output. Thereby sensory signals become selectively channeled through the brain. The latter is particularly evident in the visual system during selective attention. It has been hypothesized that coherent oscillations might underlie the selective routing of information through cortex. However, there is still no model available that captures and integrates all relevant experimental results. In particular, it is still not decided if synchronization is in fact causally involved in the gating mechanism or rather an epiphenomenon reflecting increased coupling. In this project we join as neurobiologists, theorists and engineers to attack these questions. To improve experimental access to and control of the networks under investigation we will in parallel develop, test and use a fully implantable, virtually force-free floating multi-contact electrode needle array for chronic intracortical recording and stimulation in the primate cortex. This will allow high resolution electric and visual stimulation as causal instruments to directly manipulate mechanisms putatively underlying the attention dependent selective processing of behaviorally relevant input signals as well as the effective suppression of behaviorally irrelevant signals. Simultaneously the gated signal channels can be characterized by task-irrelevant contrast modulations. This will allow us to critically test the hypothesis that gamma-band synchronization serves as gating mechanism for attention dependent routing of information.