Homotopic long-term depression of trigeminal pain and blink reflex within one side of the human face.
OBJECTIVE
Electrical low-frequency stimulation (LFS) of cutaneous afferents elicits long-term depression (LTD) of craniofacial nociception and pain. The study addresses spatial organization of LTD within one side of the face.


METHODS
The blink reflex was evoked by electrical test stimulation in the supraorbital nerve area before and after conditioning LFS in 10 healthy volunteers. Noxious LFS (1Hz) was applied to skin afferents of supraorbital (sLFS), infraorbital (iLFS), or mental (mLFS) nerves. All stimuli were applied to the same side of the face with intensities of three times pain threshold. Volunteers rated the test stimulus intensity. Each volunteer participated in four sessions with sLFS, iLFS, mLFS, or without LFS (control).


RESULTS
Pain ratings of electrical test stimulation were differently affected in experimental sessions (p<0.01) with strongest reduction by -19.6% after sLFS. The reflex integral decreased by -34.7% significantly stronger after sLFS than in all other experimental conditions (p<0.001). Electrical pain thresholds increased significantly stronger in sLFS than in iLFS, mLFS, and control (p<0.001).


CONCLUSIONS
Trigeminal nociception and pain were inhibited by homotopic LFS at the forehead but not after heterotopic LFS of infraorbital and mental nerve skin afferents.


CONCLUSIONS
Homotopic organization of ipsilateral trigeminal LTD in man may have implications for future neuromodulatory treatment of chronic craniofacial pain.
Experimental Neurosurgery Section, Department of Neurosurgery, RWTH Aachen University, Germany.
Matthias
M
Aymanns
Experimental Neurosurgery Section, Department of Neurosurgery, RWTH Aachen University, Germany; Department of Conservative Dentistry, Periodontology and Preventive Dentistry, RWTH Aachen University, Germany.
Sareh Said
SS
Yekta
Medical Physiology & Experimental Pharmacology Group, Department of Health Science and Technology, Medical Faculty, Aalborg University, Denmark. Electronic address: jellrich@hst.aau.dk.
Jens
J
Ellrich
D000328:Adult; D001767:Blinking / Q000502:physiology*; D004558:Electric Stimulation / Q000379:methods; D005145:Face / Q000502:physiology; D005157:Facial Pain / Q000175:diagnosis / Q000503:physiopathology*; D005260:Female; D006801:Humans; D036881:Long-Term Synaptic Depression / Q000502:physiology*; D008297:Male; D010147:Pain Measurement / Q000379:methods; D014277:Trigeminal Neuralgia / Q000175:diagnosis / Q000503:physiopathology*; D055815:Young Adult