fMRI Brain Representation of Non-facial Tactile Stimulation in TMD

Objectives: Patients with temporomandibular disorders (TMD) exhibit abnormal tactile sensitivities at painful and nonpainful facial sites. Mechanosensitivity might be abnormal as well on non-facial body sites, suggesting a more generalized CNS disturbance in sensory processing (Hollins and Sigurdsson, Pain 75: 59-67, 1998). To evaluate the latter, functional Magnetic Resonance Imaging (fMRI) was used to identify the cortical patterns of activation evoked by vibrotactile stimuli delivered to the finger.

Methods: Using a head-dedicated, Siemens 3T Allegra MRI system, data were collected from eleven female TMD patients (average age 28.7 yrs) and eleven gender- and age-matched controls. Diagnosis was based on RDC. Low frequency (26 Hz, 400u peak-to-peak amplitude) and high frequency (200 Hz, 200u peak-to-peak) vibration were delivered to the index finger pad on different days of testing. Stimulus events were 4s in duration and occurred every 32s for a total of 14 events/series. Two series were conducted each day. Data were processed using SPM5, and vibrotactile frequency and group-dependent effects were evaluated using random-effects models. Prior to scanning, subjects rated their present pain level from 0 (none) to 100 (most intense imaginable).

Results: Pain averaged 0.05 (std=0.21) for controls and 23.2 (std=21.8) for patients. The stimuli were highly effective in activating regions in contralateral SI, and in SII, insula, and anterior cingulate cortex (ACC) bilaterally. For TMD, 26Hz stimulation was substantially less effective in activating SI (p<.05) but more effective in activating ACC (p<0.05) than in controls. Moreover, the centers of activation in SI and in SII were shifted between the two groups of subjects. The 200Hz stimulation produced the greatest activations in SII, which did not differ between groups.

Conclusions: The results support a SI disturbance in tactile sensory processing in TMD.

Supported by NINDS grant #NS045685.