Scalp topography of ultralate (C-fibres) evoked potentials following thulium YAG laser stimuli to tiny skin surface areas in humans

Aim: To investigate (1) the scalp topography of ultralate laser evoked pote ntials (LEPs) related to C-fibre activation, which can directly be obtained by thulium YAG (Tin YAG) laser stimulation of tiny skin surface areas (abo ut 0.23 mm(2)) and (2) the influence of the performance of a motor task on ultralate LEPs. Methods: Laser stimuli were applied to the dorsum of the left hand. LEPs we re recorded with 58 scalp electrodes from 9 healthy subjects in two differe nt conditions, with and without a reaction time (RT) task (press a button u pon detection). Results: On high resolution electroenchephalogram recordings, ultralate LEP s were characterized by a broad positive component (peak latency: 1133 +/- 91 ms) with maximum amplitude about the vertex. Moreover, the performance o f a RT task had no influence on latency, amplitude and topographical patter ns of two maps chosen at the positive peak latency in ultralate LEPs. Never theless, a negative inflexion (latency 1300 ms) appeared after the positive component in the task condition possibly reflecting movement-related poten tials. Conclusion: Tm YAG laser stimulation of tiny skin surface areas allows reco rding the dynamic scalp topography of ultralate (C-fibres) LEPs, With or wi thout the performance of a RT task. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.