3D topographic study of the diode laser evoked potentials (LEPs) to painful stimulation of the trigeminal sensory area.

A diode laser attached with an optic fiber is flexible and adequate for painful cutaneous stimulation. The brain potentials elicited by diode laser stimulation reflect activation of thin-myelinated afferent fibers. This study examined the use of diode laser evoked potentials (LEPs) elicited from the left/right ophthalmic and maxillary branch of the trigeminal nerve. Twelve males (age: 26.3 +/- 4.5) participated in this study. A 20W diode laser (980 nm wavelength, 0.5 mm spot diameter) was used for stimulation. The stimulus duration was 250 ms, and inter-stimulus interval was 5 sec. The stimulus intensity was tailored to each individual eliciting mild pinprick pain. Fifty stimuli were delivered to each of the four stimulation sites. Atotal of 32 channels EEG (-1024 ms to 2048 ms) was recorded. The grand mean averages were evaluated using 3D topographic brain maps. Repeated measure ANOVA was used for statistical comparisons. Ten out of the 12 subjects resulted in a vertex component with major activations described as a negativity (-6.15 to -7.52 microV) peaking around 370 ms and a positivity (14.22 to 16.29 microV) peaking around 500 ms. This vertex potential reflected activation of the thin A-delta fiber innervating thermal and nociceptive receptors in the face. This vertex potential to diode laser stimulation may be applicable in clinical studies in patients with neurological affections of the trigeminal nerves or nucleus e.g. before and after surgery. The diode laser may be very useful for clinical neurophysiological purposes due to its applicability and user-friendly function.