Central pain in post stroke is especially good for radiologic study because one can compare the good side to the bad side. Now, it has finally been done.
No article has been more welcome thn the one in J Pain. 2005 Mar;6(3):208-12, entitled,
“Functional magnetic resonance imaging and diffusion tensor imaging in a case of central poststroke pain.”
Authors: Seghier ML, Lazeyras F, Vuilleumier P, Schnider A, Carota A.
Functional MRI allows a structural look at blood flow, creating an image of where the action is. Tensor analysis allows a look at fibers and tracts to see where connections are really going. This article is the very first to combine these two methods in Central Pain.
The authors report that fMRI showed a small hole (no blood going there) in the VPL nucleus of the thalamus.(We have already published extensive material on the ventral posterior lateral area of the thalamus here, which you can review using SEARCH) The VPL complex of the thalamus is the traditional pain processing area. There was also a cavity in the adjacent posterior limb of the internal capsule (which handles information and chemistry going to and from thalamus). Diffusion Tensor Imaging showed REDUCTION in the activity of fibers going from thalamus to the cortex. The result of this reduction of signal from the thalamus will surprise you.
Exactly WHERE in the cortex will surprise you also. There was RELEASE activity in the anterior cingulum and also, in the posterior parietal area The activity went UP in both of these areas.
The VPL thalamus quit on the brain, and the brain correctly surmised this meant trouble, and that it should construct a heavy pain signal, or at least so it would seem. Since SI was not involved, the location of the pain would be vague, just as it is in CP.
The SI-less pain is focused in the peripherae, where the brain might assume it should set up an alarm. This is speculative, however.
Repeating then, signal from thalamus to cortex went DOWN and signal activity in the anterior cingulum went UP, as did activity in the posterior parietal cortex (normally associated with SII, the so-called secondary pain area). For more understanding, you can read our review of the study of four patients by Ken Casey, elsewhere at this site, which talks about these different areas of the brain.
This is the very first study which did the testing dynamically, ie. applied some sort of thermal stimulation WHILE the study was being performed. As such, it has so much more meaning and greater worth in understanding what is going on in Central Pain.
The Journal of Pain just keeps getting better and better. Thanks to all the scientists who do this work. If anyone tells you, “It’s all in your mind”, just say, “No, it’s all in my brain, in my anterior cingulum and posterior parietal cortex.”
Finally, coming as a disappointment to all those who attribute pain to psychology and the frontal cortex, nothing much was happening there.