Functional differences can often be understood through inspection of the pattern of connections of the respective regions (Passingham, Stephan and Kotter, 2002). While there is detailed literature documenting connectivity in the monkey brain, it has to date been difficult to obtain comparable information in humans. However, using diffusion weighted magnetic resonance imaging (DWI) and probabilistic tractography, it has recently become possible to examine trajectories of white matter fibre tracts in vivo in both humans and monkeys and generate estimates of the likelihood of a pathway existing between two brain areas (Behrens, Johansen-Berg, Woolrich, Smith, Wheeler-Kingshott, et al., 2003; Hagmann, Thiran, Jonasson, Vandergheynst, Clarke, et al., 2003; Tournier, Calamante, Gadian and Connelly, 2003). Therefore, we can consider whether there are differences in the anatomical connections of the ACC and the OFC which might help explain the performance monitoring dissociations observed in the fMRI study by Walton and colleagues (2004).
