S.L. Bressler*, M. Ding, H. Liang and M. Kaminski

Center for Complex Systems & Brain Sciences, Florida Atlantic U., Boca Raton, FL 33431

Evidence from a number of sources indicates that a large-scale network of interconnected cortical and subcortical areas subserves the ability to direct attention to behaviorally relevant targets in extrapersonal space. Highly trained rhesus macaque monkeys performed a visual pattern discrimination task. Each trial was initiated when the monkey depressed a lever with the preferred hand. Computer-generated presentation of the visual stimulus began approximately 115 msec later. Surface-to-depth local event-related field potentials were recorded at distributed sites in the hemisphere contralateral to the performing hand on thousands of trials. We performed dynamic spectral analysis of the field potentials based on Adaptive MultiVariate AutoRegressive modeling. Spectral power, ordinary coherence and phase, multiple coherence, partial coherence, and directed transfer function measures were used to characterize the dynamics of field potential interdependency during the prestimulus period when the monkeys were attending to the computer screen in anticipation of stimulus presentation. The results indicate that a large-scale network of distributed cortical areas is coordinated in anticipation of stimulus appearance. This coordination occurs in the 20-30 Hz frequency range and involves sites in posterior parietal, somatosensory, and motor areas. Following stimulus presentation, this network undergoes a transition in which some of its component sites are recruited into another network that arises initially in visual cortical areas that perform visual feature processing functions. Supported by NSF Grant IBN9723240 and NIMH Grants MH58190 and MH42900.