Brain Activation In Cold Induced Toothache And Its Anticipation: Evidence From FMRI

The perception of intraoral foodstuffs involves a complex interaction of gustatory, olfactory, tactile and thermal information. A full understanding of the cerebral processing of intraoral perception requires a determination of how each of these perceptual characteristics are represented within the human brain. Although modem neuroimaging techniques provide increasingly detailed information on different aspects of visual, auditory and somatosensory processing, the functional neuroanatomy of intraoral perception include tactile, thermal and oral pain remains largely unexplored.Oral function includes mastication, gustation, sensation, pain, speech, secretion and so on, pain is one of the most important oral functions. Dental pain is the most common and special pain in endodontic clinic, which has different characteristics from body pain. The innervation density of the dental pulp is calculated to be 15 times that of skin and the sensory capabilities of the dental pulp are predominantly, but not exclusively, nociceptive. Pain arising from dental pulp is very poorly localized. A frequently encountered central excitatory effect from dental pain is a variety of muscle symptoms. While facial and body input is represented unilaterally, nociceptive input from the oral cavity has a double representation in subnucleus caudalis and oralis, All these unique features of dental pain make it significant for the insight of its central processing. Taking no account of the different nociceptive receptors and activated mechanism of nerve fibers, perception of dental pain includes nociceptive introduction, afferent information processing, translation, and regulation in the central nervous system.The previous studies of dental pain transmission pathway were mostly carried out in animals with electrical/thermal stimulation and pulpitis animal models. The problemexists that results from animal study may not totally reflect the dental pain pathway in humans, especially in the cerebral cortex. Pain perception is subjective, which may not be described in animal study, the correlation between pain rating and nerve activation intensity may not easily be evaluated in none human studies. Though electrophysiological techniques such as electroencephalogram(EEG), magnetoencephalography(MEG) can be non invasively used in human brain research, its low spatial resolution make it impossible to see the detailed anatomy of brain activity. Functional magnetic resonance imaging(fMRI) is an advanced non invasive neuroimaging technique which has high spatial and temporal resolutions, and has been rapidly developed these years. It has been extensively used in the exploration of cerebral activities in auditory, visual, sensory, motor and cognitive procedures. The emerging of fMRI allows investigators to assess functional -anatomical concordances bilaterally and three-dimensionally and there promise to offer further insight into dental cortical representation.Dentinalgia or dentinal pain is a kind of dental origin pain except for pulpalgia and periodontal pain. It can be transiently induced by thermal, air current or physical traumatic injury and disappears once the stimulus withdraw, it may not occur spontaneously, so it's an ideal stimulated pain model in human dental pain research. Cold water stimulation can evoke pain sensation in patients with dentinalgia, but not in patients with healthy teeth. In this study, we employed high spatial resolution neuroimaging method fMRI to explore cerebral activation in dentine pain stimulation with cold water non invasively, and primarily evaluated cortical response in intraoral cold water sensation.Pain is an unpleasant sensation and emotional experience related to actual or potential injury. Dental pain perception is an complex process not only with neurophysiological changes but also involving emotional, behavioral and cognitive factors. It can be strongly influenced by the past experience and pain memory. Expectation of pain is a complex state that may influence the immediate unpleasantness of pain, and by itself may be an important factor in the development of chronic oral facial pain syndromes. So, in thisstudy, we also tried to figure out how the human cortex decodes the information of impending dental pain stimuli, which may provide psychological reference in dental treatment.This study consists of the following three parts:1. Cortical responses of intmoral cold water stimulation measured with IMRI Objective: To discuss the neural representations of intra-oral stimulation with cold water with non-invasive fMRI measurements, and provide a contrast for dental pain study. Methods: 8 right handed volunteers with healthy full and vital dentition were recruited to receive cold water stimulation on first right upper bicuspid(N-R). Self-made plastic tube was employed to introduce cold(4-6℃) deionized water to the subjects' mouth, block designed BOLD functional MRI scan covering the whole brain was carried out. The fMRI data were analyzed by SPM2 software with statistic t-test to generate the activation map. Results: Increased BOLD signals during intra-oral cold water stimulation were found in sensory/motor and premotor cortex(BA3,4,6), inferior parietal lobule, precuneus(BA7,40) and basal ganglia. Conclusions: 1.None gustatory intra-oral cold water stimulation can excite the primary sensory motor cortex, besides, many other cortex may take part in the process of intra-oral cold water input. 2.The neural projection of intra-oral cold sensation can reach both hemispheres, but dominantly contralateral in SI/MI and ipsilateral in parietal lobule.2. Brain activation in cold induced toothache: evidence from IMRIObjective: To evaluate the feasibility of fMRI on the location of brain regions related to cold stimulated toothache. Distinguish the different brain regions between intra-oral pain perception and cold sensation. 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 which 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 patient dental pain group(P-R) showed significant bilateral activations especially in insula/SII, basal ganglion, cingulate gyrus/SMA, midbrain red nucleus. BOLD signals were also found unilaterally in rightthalamus, inferior parietal lobule/BA7, BA40. Signials in Broca motor language area BA44,MII/PMC/BA4,6 were weak in the fight side but were strongest in the left side. In contrast, the normal group (N-R) who receive cold water on the left side showed increased signals in bilateral PMC and inferior parietal lobuleBA40. Left lentiform nuleus, left SI/MI /MII/PMC and right precuneus/BA7 were also excited in none painful sensation. The activation in fight inferior parietal lobule BA40 was stronger than that in the left side. Cold water to the patients left bicuspid (P-L) evoked right pre/post central gyrus SI/ML MII/PMC. insula/SII, basal ganglion, and left precentral gyrus MII/PMC, Broca BA44, as well as both sides inferior parietal lobule BA40. Conclusions: 1 .Specific functional regions of the human brain cortex can be activated in fMRI study when the cold stimulated dentin pain is induced; 2.These results agree with previous neuroimaging findings in somatotopic pain perception, except for that motor cortex including PMC, SMA and Broca BA44 have strong signals during dental pain, The broad activation in motor 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. 3. Functional activity mapping during anticipation of dental pain Objective: To reveal functional activity mapping during anticipation of dental pain with non-invasive fMRI technique, and offer therapeutic possibilities for treating chronic oral facial pain psychologically. Methods: 8 right handed patients with dentinalgia of the right maxillary bicuspid took part into this study. Block design were adopted, BOLD level during anticipation epoch(on) was contrasted with that of rest(ofi). Scanning and analysis procedure were the same with study 1.Results: Increased BOLD signals during dental pain anticipation were found dominantly on the left side in inferior, middle frontal gyrus/BA 10,46, postcentral gyrus/BA2,3, middle frontal gyrus/BA8, precentral gyrus/BA44 and cerebellum. Conclusions: 1. Anticipation of dental pain by itself can activate brain regions, especially prefrontal areas, SI, SMA and cerebellum;...