Furey, Maura L. and Ricciardi, Emiliano and Schapiro, Mark B. and Rapoport, Stanley I. and Pietrini, Pietro Cholinergic Enhancement Eliminates Modulation of Neural Activity by Task Difficulty in the Prefrontal Cortex during Working Memory. Journal of Cognitive Neuroscience, 20 (7). pp. 1342-1353. ISSN 0898-929X (2008)