Fiona,
I'm aware of the imaging studies you cite, and feel they do fit quite nicely with experience of the stimulants being helpful for the attentional problems. What I have not seen are SPECT studies designed to see what each of the innate affects looks like. Tomkins used rapid video cameras to look at the face in each of the affects, and even some skin temperature studies may have been done. Someone needs to put some people into a SPECT scanner and then embarress the heck out of them. For all I know we might see a decrease in perfusion of the periventricular areas and an increase in the occipital areas.
We are not saying that ADHD patients don't exhibit shame, but rather that they exhibit it in ways that many therapists don't recognize as part of the innate affect that Tomkins called Shame/Humiliation. The state of chronically not quite getting what's going on around one results in chronically activated shame affect.
Affect is required to provide the amplification necessary to attend to anything. I certainly hope the neuroimaging community starts to attend to the affects.