Brain activation in cold induced toothache: evidence from fMRI

Objective: To explore the location of brain regions related to cold stimulated toothache with noninvasive fMRI technique. Methods: 8 patients with cold induced dentinalgia of the right maxillary bicuspid and 8 healthy volunteers with full and healthy dentition were selected to perform the fMRI study, all of whom are right handed. A plastic tube was employed to induce toothache, and block designed BOLD functional MRI scan covering the whole brain was carried out. Results: The patients of dental pain group(P-R) showed significant bilateral activations especially in insula/SII, basal ganglion, cingulate gyrus/SMA, PMC, midbrain red nucleus. BOLD signals were also found unilaterally in right thalamus, inferior parietal lobule(BA7, BA40). Signals in Broca speech language area BA44, MII/PMC/BA4,6 were weaker on the right hemisphere compared with left hemisphere. In contrast, normal group (N-R) who received cold water on the left side showed increased signals in left lentiform nuleus, left SI/MI, MII/PMC and right precuneus(BA7). Activation on the right inferior parietal lobule(BA40) was stronger than that on the left side. Conclusions: 1.Specific regions of the human brain cortex can be activated in fMRI study when the cold stimulated dentine pain is induced; 2.These results agree with previous neuroimaging findings in body pain perception, except for that motor related cortex including PMC, SMA and Broca BA44 have strong signals during dental pain. The broad activation in motor related areas may be related to escape reaction, initiative head control and automatic tongue and jaw movements; 3.Compared with body pain, tooth pulp stimulation evoked a more pronounced activation in the ipsilateral hemisphere in some brain regions, such as insula/SII, singulate gyrus, which may indicate a more widely spread cerebral pain processing of sensory input from trigeminal nerves than from peripheral body regions.