The present proposal aims to combine state-of-the-art integrated transcranial brain stimulation, electroencephalographic recording techniques with genetics and computational modeling to unveil the mechanisms underlying a fundamental cortical network process - synchronization of neuronal activity in the gamma band (30-80 Hz) - and the sources of its intersubject variability. By measuring the entrainment of prefrontal cortex produced by weak oscillatory currents, the study team will provide a new non-invasive strategy to derive robust estimates of the cortical ability to support gamma oscillations, critically overcoming limitations associated with current approaches and allowing measures solely dependent on intrinsic regional cortico-thalamic properties. Consistent with molecular evidence and the investigators biophysical models of gamma oscillations, the study team expects that such unambiguous measurement of cortical capabilities will straightforwardly map onto key genetic underpinnings related to the dopamine and neuregulin signaling pathways. These computational models will be used to offer critical mechanistic insights linking genetic variations to variability in emergent circuit-level activity in the form of cortical gamma oscillations.