Commonly used interdependency measures such as cross correlation and spectral coherence do not yield directional information.Phase spectra may be used for that purpose only under very ideal conditions.Recent work has begun to explore the use of causal measures to further dissect the interaction patterns among neural signals.In this talk I will describe the concept of Granger Causality and introduce Geweke causality spectra.The technique will then be applied to the analysis of multichannel local field potentials recorded from behaving monkeys performing sensorimotor and selective attention tasks.